Research Progress on Comprehensive Utilization of Silkworm Excrement Bioresource

Abstract

With the vigorous development of sericulture, the traditional labor-intensive small-scale silkworm rearing has been progressively transformed into a large-scale mechanized system. Consequently, silkworm factories can produce cocoons continuously throughout the year. However, this intensive production pattern generates a substantial amount of silkworm excrement. If not managed properly or disposed indiscriminately, silkworm excrement can lead to severe environmental pollution. In recent years, increasing attention has been paid to the comprehensive utilization of this bioresource. Numerous studies have explored its potential in a wide range of applications. This review systematically summarizes current research on silkworm excrement utilization, particularly focusing on its fundamental characteristics, key technologies, and application areas. Future efforts should aim to promote efficient resource recycling and support the development of sericulture.

1. Introduction

Raising edible insects can enhance food security and promote economic development, particularly in developing countries [1,2,3,4,5]. Among these, the domestic silkworm (Bombyx mori) is a key economic insect, not only for its efficient silk production, but also because its pupae serve as a nutritious biological resource that can be used as food supplements, pharmaceuticals, and health products [6]. In recent years, sericulture has gradually shifted from traditional, labor-intensive small-scale operations to large-scale mechanized rearing systems, enabling year-round, uninterrupted cocoon production. However, this intensification generates large quantities of sericulture excrement (insect feces), estimated at 20,000 tons annually per factory [7], posing serious environmental challenges. Moreover, silkworm excrement harbors a variety of microorganisms, including silkworm pathogens such as nucleopolyhedroviruses, Bacillus thuringiensis, and Beauveria bassiana [8]. Without proper scientific treatment and disposal, these pathogens may cause potential silkworm disease outbreaks through the silkworm excrement–soil–mulberry–silkworm transmission chain [7,9].

Silkworm excrement is increasingly recognized as a sustainable and valuable resource [10,11]. Historically, it was used as a traditional Chinese medicine known for dispelling wind and removing dampness [12]; and in agriculture, it has also served as fish feed in Mulberry-Dyke and Fish-Pond system for millennia [13]. However, these traditional recycling methods are only suitable for small-scale sericulture. With the advent of large-scale, modern sericulture, there is now an urgent need for more efficient strategies to manage the substantial volumes of silkworm excrement generated. Since the 21st century, with the development of biotechnology, the scientific challenge of how to fully utilize silkworm excrement to mitigate its environmental impact has garnered significant interest [14] (Figure 1). This study focuses on the comprehensive utilization of silkworm excrement, systematically exploring its fundamentals, key technologies involved, and the latest research progress. The aim is to provide new perspectives on efficiently utilizing silkworm excrement and establishing a recycling economic system.

2. Literature Search Strategy

An electronic literature search was conducted using CNKI (China National Knowledge Infrastructure), Web of Science, Bing Scholar, and PubMed until June 2025. Additional articles were identified and obtained from references in the retrieved articles. Search terms included combinations of the following: silkworm excrement, silkworm, extraction, fermentation, etc. For the purpose of this review, the search was restricted to experimental, in vitro, in vivo, and clinical studies published in Chinese and English that address the silkworm excrement utilization, particularly focusing on its fundamental characteristics, key technologies, and application areas.

3. Basic Properties of Silkworm Excrement

Silkworm excrement is a by-product resource characterized by its high production volume and low cost. It is the primary waste generated during silkworm rearing. According to reports, China produces up to 4.5 million tons of silkworm excrement annually [15]. In order to effectively utilize silkworm excrement, it is essential to understand its fundamental properties. In appearance, silkworm excrement is a short, cylindrical, granular solid with a diameter of approximately 2.2 mm and a length of about 3.5 mm. It has a slight grassy odor and a grayish-black, rough surface, marked by six longitudinal ridges and three to four shallow transverse lines. The ends are slightly flattened in a hexagonal shape, and the substance is hard but friable [16]. Microstructurally, silkworm excrement mainly consists of cellulose and proteins arranged in an ordered structure. It contains a high carbon content with a unique nano lamellar morphology, endowing it with a wide range of applications in the materials field [17].

From the chemical perspective, silkworm excrement contains 59.2% moisture. Its dry matter contains 15.4% crude protein (CP), 3.88% ether extract (EE), 36.2% nitrogen-free extract (NFE), and 19.6% crude fiber (CF). It also comprises 0.58% calcium, 0.82% phosphorus, and a variety of minerals, such as iron (Fe), cobalt (Co), manganese (Mn), copper (Cu), and zinc (Zn) [18,19]. In addition, it is rich in various bioactive compounds, including chlorophyll, pectin, flavonoids, alkaloids, adrenocorticotropic hormones, and vitamins (A, B, C, D, E, and niacin). It also contains steroids (e.g., sterols, cholesterol, and gluteninol) and antimicrobials such as protocatechuic acid and p-hydroxybenzoic acid (Figure 2) [19].

Silkworm excrement also contains a highly diverse microbial community [9], with many microorganisms showing potential for industrial and agricultural applications. For example, Bacillus licheniformis, Bacillus amyloliquefaciens, and Bacillus subtilis, isolated from silkworm excrement, have demonstrated strong cellulose-degrading abilities [8]. Additionally, Klebsiella pneumoniae and Bacillus licheniformis isolated from silkworm excrement compost have been shown to promote both plant and silkworm growth [7].

4. Key Technological Advances in the Comprehensive Utilization of Silkworm Excrement

4.1. Extraction Technology

Extraction technology refers to the process of isolating, purifying, and concentrating target compounds from biological materials using physical, chemical, or biological methods [20,21]. As early as 1964, it was employed to extract chlorophyll and carotenoids from silkworm excrement [20]. However, traditional extraction techniques depend on water or organic solvents, which have several disadvantages, including low efficiency, lengthy processing times, low extract concentrations, and solvent residues [21]. To address these issues, several innovative and emerging extraction techniques have been developed (

Table 1. Novel and emerging extraction techniques for the comprehensive utilization of silkworm excrement.

Technology	Principle	Advantages	Limitations	References
Supercritical fluid extraction technology	Utilizing supercritical fluids’ excellent solubility and diffusivity to penetrate plant cell walls efficiently.	Achieving efficient extraction of natural active ingredients at lower temperatures with no solvent residue.	It has shortcomings such as insufficient selectivity and difficulty in extracting strongly polar substances and substances with large molecular weights.	[21,22,23]
Ultrasonic-assisted extraction technology	Ultrasonic waves destroy the cell wall structure to increase the permeability of the cell wall, thereby achieving efficient extraction.	It boasts high extraction efficiency, short extraction times, and effectively preserves the active ingredients.	It easily causes the extraction temperature to rise, leading to the decomposition of heat-sensitive substances and resulting in the loss of active ingredients.	[21,24,25]
Microwave-assisted extraction technology	Leveraging both the thermal and non-thermal effects of microwave radiation, the extraction process is accelerated, and its efficiency is enhanced.	It offers advantages such as a short time frame, high efficiency, and a simple process, which saves energy consumption and can be implemented in large-scale production plants.	It has shortcomings that need improvement, such as requiring additional cleaning steps and having limitations with polar solvents.	[21,26,27]
Ultra-high-pressure technology	Excessive pressure alters plant materials’ structure and enhances cell wall permeability.	It has obvious advantages, such as high operability, short use time, energy savings, environmental protection, being green and pollution-free, and being able to extract heat-sensitive compounds.	The equipment cost is high, and the maintenance expense is substantial; high pressure may damage the structure of macromolecules such as polysaccharides, affecting their biological activity.	[21,28,29]
Enzyme-assisted extraction technology	An enzyme’s catalytic action destroys the structure of the plant cell wall to release active ingredients in cells and achieve efficient extraction.	Enzymes can improve extraction efficiency, shorten extraction time, and reduce the use of organic solvents.	Enzyme preparation costs are high; the extraction solution contains numerous impurities such as polysaccharides and proteins.	[21,30,31]

).

4.2. Fermentation Technology

Fermentation technology involves the transformation of organic substances into substances via microbial metabolic processes [32]. It is widely used in the comprehensive utilization of silkworm excrement, helping to eliminate pathogenic microorganisms and convert organic matter into stable humus, thus providing essential materials for the production of high-quality organic fertilizers [33]. Additionally, fermentation enables the generation of biogas from silkworm excrement, thereby reducing dependence on fossil fuels [34].

Beyond serving as a fermentation material, recent studies have shown that silkworm excrement can also enhance the expression of specific microbial genes, thereby improving the yield or quality of fermentation products. For example, Haloferax mediterranei can accumulate poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Adding an appropriate amount of silkworm excrement can enhance the expression of genes related to the aspartic acid/2-ketobutyrate pathway, which is associated with the synthesis of 3-hydroxyvalerate (3-HV). Higher 3-HV content can further enhance the extensibility of PHBV and lower its melting point [34]. Silkworm excrement is an agricultural waste and relatively cheap. If silkworm excrement is used to replace some of the glucose as a fermentation raw material, the cost of fermentation can be greatly reduced. However, there are few studies on the production of high value substances by fermentation of silkworm excrement. In the future, the fermentation process of silkworm excrement needs to be further developed and optimized.

4.3. Biochar Technology

Under oxygen-free conditions, agricultural wastes can be converted into biochar through high-temperature pyrolysis, gasification, hydrothermal carbonization, or microwave pyrolysis [35,36,37]. Biochar has the potential to serve as an effective adsorbent material, catalytic material, and slow-release fertilizer, owing to its unique properties such as a rich pore structure, stable chemical properties, large specific surface area, diverse surface-active functional groups, high carbon content, and high cation exchange capacity [37,38,39]. Additionally, the high specific surface area, high energy density, high electrical conductivity, and excellent cyclic stability of biochar, along with its stable, highly aromatic, carbon-rich, and eco-friendly characteristics, indicate significant potential for applications in supercapacitors, storage batteries, fuel cells, electrochemical sensors, biosensors, and EMI shielding materials [37,40].

Silkworm excrement, mainly composed of cellulose and proteins with an ordered structure, high carbon content, and a unique nano-flake morphology, is an excellent raw material for preparing biochar composites [17]. Furthermore, as an agricultural waste, it is highly cost-effective and requires no pre-crushing due to its naturally small particle size, offering additional advantages for biochar production [38]. Despite these advantages, the process of preparing biochar from silkworm excrement requires more energy, which limits the application of silkworm excrement-based biochar.

4.4. Omics Technologies

Metabolomics technology is a technology that systematically studies the composition and dynamic changes in all metabolites within organisms by integrating methods such as mass spectrometry (MS), nuclear magnetic resonance (NMR), and chromatographic separation [41]. Using metabolomics technology, we can infer specific medicinal components in traditional Chinese medicine and their mechanisms of action, thereby promoting the development of corresponding drugs [42]. As a typical traditional Chinese medicine, silkworm excrement is rich in various pharmacologically active components. For example, its β-carotene has been proven to have significant tumor-inhibiting effects [43]. With the aid of metabolomics technology, we are expected to gain a deeper understanding of the components in silkworm excrement and further explore its potential medicinal value [44].

Microbiomics technology has also been widely applied to utilize silkworm excrement resources. This technology primarily relies on high-throughput sequencing and mass spectrometry identification rather than traditional microbial cultivation, and it has now been extensively used in studying various fields such as soil, water bodies, the atmosphere, and the human body [45]. By employing microbiomics technology, we can conduct in-depth research on the impact of silkworm excrement as feed or medicine on animal intestinal microbiota, thereby revealing its nutritional or medicinal value [19,46]. Furthermore, microbiomics technology can provide robust support for investigating the influence of silkworm excrement as fertilizer on soil microorganisms and its role as an eco-friendly material in ecological environment remediation [47,48].

5. Comprehensive Utilization of Silkworm Excrement

5.1. Silkworm Excrement Serves as Animal Feed

Feed constitutes one of the major costs in animal production. Among feed ingredients, corn is widely used and is priced at approximately 2920 RMB per ton [49]. In contrast, the market price of fermented silkworm excrement is only 600 RMB per ton, and when processed independently by sericulture farmers, the cost can be reduced to as low as 60 RMB per ton [50]. Consequently, using silkworm excrement as a partial substitute for corn feed can effectively manage silkworm waste, reducing environmental pollution, significantly lowering production costs, and enhancing economic benefits.

Previous studies have indicated that for animals such as pigs, rabbits, ruminants, poultry, and aquatic species, incorporating appropriate quantities of silkworm excrement into their feed can enhance feed palatability and promote growth [51]. It can also improve the quality of animal products, including enhancing the muscle organoleptic qualities, such as luster, juiciness, and tenderness, as well as reducing the muscle shear force [19].

When used as animal feed, silkworm excrement can also benefit animal health. Firstly, the flavonoids, polyphenols, and vitamins present in fermented silkworm excrement possess antioxidant properties, which help reduce cell and tissue damage and improve abnormalities in sugar and lipid metabolism in animals. Additionally, the probiotics from fermented silkworm excrement can colonize the intestinal tract, regulate intestinal microbiota by competing with pathogenic bacteria for nutrients, produce antimicrobial substances, and alter the intestinal pH to maintain intestinal health [51].

Through biotransformation, silkworm excrement can be transformed into protein feed. It serves as an excellent substrate for earthworm cultivation, exhibiting comparable effects on survival rates, average daily weight gain, and reproduction to those observed with cow dung [52]. In addition, silkworm excrement can be utilized as a rearing medium for black soldier fly larvae. Chen et al. [53] demonstrated that optimal conversion occurs at a 65% moisture content and a rearing density of 25 g/kg for 4-day-old larvae. Furthermore, the residue from silkworm excrement processed by black soldier flies can be repurposed as organic fertilizer.

However, silkworm excrement contains nitrites and anti-nutritional factors that could adversely affect animals [51]. To mitigate these risks, it is essential to scientifically determine appropriate addition levels and apply treatments such as fermentation or heating [50]. Research indicated that incorporating 10% fermented silkworm excrement into feed can notably enhance the muscle protein, amino acid content, and the textural properties without impacting growth. However, addition rates exceeding 15% sharply reduce growth performance and digestive capacity. Additionally, moderate amounts of fermented silkworm excrement can improve non-specific immunity in grass carp, whereas excessive levels may induce intestinal inflammation [54,55].

5.2. Silkworm Excrement Serves as Fertilizer

Utilizing silkworm excrement as a fertilizer can improve soil fertility and promote healthy crop growth [33]. Studies have shown that applying silkworm excrement organic fertilizer can significantly increase soil enzyme activities, promote the conversion of organic matter into humus, and improve the physical and chemical properties of soil [56,57,58,59]. Compared to compound fertilizers, silkworm excrement fertilizers provide a more sustained release of nutrients, reduce organic matter loss, and increase total nitrogen and potassium content in the soil [60]. Moreover, silkworm excrement organic fertilizer can also increase the abundance and diversity of soil microflora, particularly the Proteobacteria and Actinobacteria [47]. Specific components in silkworm excrement fertilizer may also help suppress plant pests and diseases; for instance, the alkaloid DNJ has been shown to control sugarcane pests [61].

The use of silkworm excrement as a fertilizer can also reduce heavy metal accumulation in crops. It has been found that silkworm excrement fertilization significantly reduces Cd and As concentrations in rice grains grown in contaminated paddy fields. Specifically, silkworm excrement decreases heavy metal accumulation by increasing soil pH, conductivity, and organic matter content, altering bacterial community composition, and promoting iron plaque formation [62,63,64,65].

Shen et al. [7] demonstrated that silkworm excrement is an efficient biofertilizer and a reservoir rich in beneficial microorganisms. Many microorganisms isolated from silkworm excrement exhibit strong potential in plant growth promotion, biocontrol, and use as feed additives, providing a material basis for developing microbial fertilizers [7,66]. For example, Zhou et al. [67] isolated nine strains from silkworm excrement, including Acinetobacter sp., Pseudomonas sp., Kluyvera sp., and Saccharopolyspora sp., among which the strongest strain achieved a phosphorus-solubilizing capacity of 113.8 mg/L.

5.3. Silkworm Excrement Serves as Traditional Chinese Medicine

Silkworm excrement, as a traditional Chinese medicinal material, exhibits certain therapeutic effects for various diseases (

Table 2. Therapeutic applications of silkworm excrement in various diseases.

Disease Category	Subtype of Disease	Active Components/Related Extracts of Silkworm Excrement	Mechanism of Action	References
Traditional Chinese Medicine diseases	Fever (temperature-lowering effect)	Water decoction of bamboo shavings, silkworm excrement, and tangerine peel	Exhibits more effective temperature-lowering effect than aspirin, with less stimulation to the gastrointestinal tract, liver, and kidneys; mechanism may be associated with impacting levels of mediators (noradrenaline (NA), 5-hydroxytryptamine (5-HT), dopamine (DA)) affecting the thermoregulatory center	[69]
	Syndrome of damp retention in the middle-jiao	Fagomine, 3-epi-fagomine, astragalin, quercitrin in silkworm excrement	Regulates aquaporin expression, playing a “dampness-resolving” role; mechanism may be related to the cAMP-PKA-CREB signaling pathway	[44,46,70]
Insomnia	Insomnia (neurological disorder)	Geranylacetone, farnesylacetone, phytol, phytone, isoquercitrin, GABA, glutamic acid, butyric acid	Targets specific receptors and modulates signaling pathways (e.g., GABAergic signaling pathway), thereby effectively alleviating insomnia.	[71,72]
Diabetes mellitus	Type II diabetes (T2D)	Alkaloids such as 1-Deoxynojirimycin (1-DNJ) in silkworm excrement	Inhibits glucose absorption in the small intestine by suppressing α-glucosidase activity; lowers blood glucose by modulating hepatic enzymes involved in glucose metabolism; key pathway involves AMPK/PI3K/Akt signaling pathway	[73,74,75,76]
	Diabetic gastroparesis (DGP)	Silkworm excrement extract	Modulates the PI3K/Akt/mTOR signaling pathway to increase gastric emptying rate, attenuate apoptosis of Cajal mesenchymal stromal cells, and reduce stochastic blood glucose levels in rats with DGP	[77,78]
Cancer	Colon cancer	Lupeol (isolated from silkworm excrement)	Has significant anti-inflammatory and anti-tumor effects; inhibits proliferation, migration, and invasion of colon cancer cells HCT116 by suppressing IL-6/JAK2/STAT3 pathway activation and down-regulating pro-inflammatory factor expression.	[79,80]
	Radiation/chemotherapy-induced bone marrow suppression	Silkworm excrement extract	Promotes stem cell factor secretion, activates JAK2/STAT3 signaling pathway, and facilitates bone marrow repair, thereby alleviating bone marrow suppression.	[81,82]
Anemia	Iron deficiency anemia	Shengxuening (SXN) tablets (derived from silkworm excrement)	Demonstrates efficacy in treating iron deficiency anemia with a proven safety record	[83,84,85]
	Renal anemia (especially in patients undergoing maintenance hemodialysis)	Shengxuening (SXN) tablets (derived from silkworm excrement)	Effective in treating renal anemia, including that in patients undergoing maintenance hemodialysis, with a proven safety record	[84,85,86,87]
Migraine	Migraine (neurological disorder)	Petroleum ether extract of silkworm excrement (phytol as key component)	Phytol blocks the inactivation state of Nav1.7 sodium channel, shows high selectivity for Nav1.7, weak antagonism for TRPV1 and TRPA1 channels, and is independent of local anesthetic action sites.	[88,89]
Arthritis	Rheumatoid arthritis (RA)	Aqueous and ethanolic extracts of silkworm excrement	Regulates six significantly associated metabolic pathways, restoring 33 endogenous metabolites (e.g., succinic semialdehyde, stearic acid, adrenergic acid) to a certain extent.	[90,91]

). However, research on the toxic side effects of silkworm excrement remains insufficient, and the key therapeutic targets for specific diseases and their regulatory mechanisms still require further investigation and experimental validation [68].

5.3.1. Traditional Chinese Medicine Diseases

The water decoction of bamboo shavings, silkworm excrement, and tangerine peel is a traditional Chinese medicine folk prescription. It was found that the decoction had a better hypothermic effect than aspirin for yeast-induced fever in rats, and had less irritation to the gastrointestinal tract, liver, and kidney (p < 0.05). The mechanism of action may be associated with its impact on the levels of mediators such as noradrenaline (NA), 5-hydroxytryptamine (5-HT), and dopamine (DA), which affect the thermoregulatory center [69]. Although this conclusion has been confirmed in preclinical rat models, it still needs to be verified by human clinical trials.

Syndrome of damp retention in the middle-jiao is a pathological state described in Chinese medicine, primarily caused by the accumulation of internal dampness [44]. Clinical manifestations include symptoms such as limb heaviness, fatigue, a thick and greasy tongue coating, reduced appetite for food and drink, a feeling of distension and fullness in the epigastrium, and loose stools [46]. Research has indicated that silkworm excrement has therapeutic effects on the syndrome of damp retention in the middle-jiao. Wang et al. [70] discovered that silkworm excrement could regulate the expression of aquaporin, playing a role in “dampness-resolving”. Compounds such as fagomine, 3-epi-fagomine, astragalin, and quercitrin found in silkworm excrement may be the active ingredients, and the mechanism of action may be related to the cAMP-PKA-CREB signaling pathway.

5.3.2. Insomnia

Insomnia is a prevalent and common neurological disorder, and chronic insomnia may lead to depression and anxiety [71]. Utilizing a network pharmacology approach, Gong et al. [72] discovered that the core components of silkworm excrement included geranylacetone, farnesylacetone, phytol, phytone, isoquercitrin, GABA, glutamic acid, and butyric acid. Those core components could target specific receptors and modulate signaling pathways, such as the GABAergic signaling pathway, thereby effectively alleviating insomnia.

5.3.3. Diabetes Mellitus

Diabetes mellitus is a metabolic and endocrine disease characterized by hyperglycemia, with more than 90% of cases being type II diabetes (T2D) [73]. As a traditional Chinese medicine, silkworm excrement contains alkaloids such as 1-Deoxynojirimycin (1-DNJ), which have been proven to inhibit glucose absorption in the small intestine by suppressing α-glucosidase activity and to lower blood glucose levels by modulating the expression of hepatic enzymes involved in glucose metabolism [74,75]. Duan et al. [76] revealed the AMPK/PI3K/Akt signaling pathway as a key pathway of silkworm excrement’s anti-type II diabetes effects through a combination of network pharmacology and experimental confirmation.

A common complication in diabetic patients is diabetic gastroparesis (DGP), characterized by symptoms such as delayed gastric emptying [77]. Studies have shown that silkworm excrement extract has the effect of alleviating diabetic gastroparesis. It may alleviate the condition by modulating the PI3K/Akt/mTOR signaling pathway to increase the gastric emptying rate, attenuate the apoptosis of Cajal mesenchymal stromal cells, and reduce the stochastic blood glucose level in rats with diabetic gastroparesis [78].

5.3.4. Cancer

Colon cancer is one of the primary cancers that threaten human life and health [79]. Lupeol, isolated from silkworm excrement, has been shown to have significant anti-inflammatory and anti-tumor effects. Lupeol inhibits the proliferation, migration, and invasion of colon cancer cells HCT116 by suppressing the activation of the IL-6/JAK2/STAT3 pathway and down-regulating the expression of pro-inflammatory factors [80].

Radiation and chemotherapy, common treatments for cancer, often lead to bone marrow suppression, resulting in anemia, infection, and other complications. This significantly impacts treatment efficacy and increases the medical burden [81]. Ding et al. [82] demonstrated that silkworm excrement extract could promote bone marrow repair by enhancing stem cell factor secretion and activating the JAK2/STAT3 signaling pathway, thereby alleviating radiation-induced bone marrow suppression.

5.3.5. Anemia

Iron deficiency anemia is the most common form of anemia globally, affecting over one billion people and being particularly prevalent in Asia [83]. Renal anemia, by contrast, is a common complication among patients with chronic kidney disease, particularly those undergoing maintenance hemodialysis (MHD). This condition can worsen anemia and diminish the effectiveness of recombinant human erythropoietin (rHuEPO) [84,85]. In recent years, Shengxuening (SXN) tablets, derived from silkworm excrement, have demonstrated efficacy in treating both iron deficiency anemia and renal anemia, with a proven safety record [86,87].

5.3.6. Migraine

Migraine is a common neurological disorder affecting approximately 11% of adults worldwide [88]. Song et al. [89] identified the potent anti-migraine activity in the petroleum ether extract of silkworm excrement using a rat model of nitroglycerin-induced migraine. Among the seven isolated compounds, phytol had a significant anti-migraine effect. Phytol can block the inactivation state of the Nav1.7 sodium channel, showing high selectivity for the Nav1.7 sodium channel, weak antagonism for TRPV1 and TRPA1 channels, and independence from local anesthetic action sites.

5.3.7. Arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease that severely affects patients’ quality of life [90]. Zheng et al. [91] investigated the therapeutic effects of aqueous and ethanolic extracts from silkworm excrement in a rat model of Freund’s adjuvant-induced arthritis. Using metabolomics techniques, they identified six significantly associated metabolic pathways and 33 endogenous metabolites, including succinic semialdehyde, stearic acid, and adrenergic acid. These biomarkers were restored to a certain extent following the intervention with the aqueous extract of silkworm excrement.

5.4. Chemical Engineering

In the chemical industry, silkworm excrement can be employed to produce chemical raw materials through extraction, such as chlorophyll, pectin, flavonoids, lutein, and β-carotene. It can also be used to prepare corrosion inhibitors, novel cosmetics, dyes, and cigarette additives by easy extraction. Additionally, it can serve as a cost-effective microbial carbon source for producing other high-value substances like PHBV and pectinase (Figure 3). Although silkworm excrement can be used in various fields of chemical industry, silkworm excrement is mainly used for industrial extraction at present. Future research should try to use silkworm excrement as a carbon source and realize high-value utilization of silkworm excrement by means of synthetic biology.

5.4.1. Production of Chlorophyll

Chlorophyll, an essential natural pigment, is extensively utilized in the food, pharmaceutical, textile, and daily chemical industries [92]. However, its limited water solubility and stability hinder its practical applications [93]. Silkworm excrement is currently considered the raw material with the highest chlorophyll content, making it the best material for extracting chlorophyll [94]. Zhang et al. [93] synthesized the zinc sodium salt of silkworm excrement chlorophyll through a series of reactions, including chlorophyll saponification, acid generation, zinc substitution, and salt formation. This process enhanced the water solubility and heat resistance of chlorophyll. Han et al. [95] optimized the ultrasonic-assisted extraction process of chlorophyll from silkworm excrement using one-way and orthogonal tests. The experimental conditions optimized were as follows: at 25 kHz, 90% ethanol was used as the extraction solution, the ratio of material to liquid was 1:12 (g/mL), and the ultrasonic time was 50 min. Cui et al. [96] employed response surface methodology to optimize the ethyl acetate extraction process of chlorophyll from silkworm excrement, significantly increasing the chlorophyll extraction yield to 61.78%.

5.4.2. Production of Pectin

Pectin, an important natural polysaccharide, has a wide range of applications across the food, pharmaceutical, and chemical industries [97]. It could be extracted from silkworm excrement using the iron salt method, and the 90% confidence interval for pectin yield was found to be between 3.52% and 4.49% [98]. The ideal conditions for extracting pectin from silkworm excrement, established through one-way and orthogonal tests, include the following: hydrolysis using 0.25% oxalic acid at a solid–liquid ratio of 1:20 (g/mL), a pH of 1.5, a temperature of 85 °C, a duration of 60 min, and the precipitation conditions are a pH of 3.5 with an iron salt concentration of 0.5%, resulting in a pectin yield of 5.21% ± 0.05% [99].

5.4.3. Production of Flavonoids and 1-Deoxynojirimycin

Flavonoids constitute a class of natural polyphenols that are abundantly present in plants and exhibit a range of biological activities [100]. Li et al. [101] utilized an orthogonal test and resin purification technique to extract flavonoids from silkworm excrement, achieving an extraction rate of 6.43 mg/g. Yu et al. [102] extracted flavonoids from the waste residue left after chlorophyll extraction from silkworm excrement, determining the optimal conditions for the process to be boiling extraction with pure water, a material-to-liquid ratio of 1:10, and an extraction time of two hours. One of the active ingredients in silkworm excrement that exhibits an antidiabetic effect is 1-deoxynojirimycin (DNJ) [103]. Lv et al. [104] utilized 0.1 mol/L hydrochloric acid as the extraction solvent, with an 80 °C extraction temperature and a two-hour duration, achieving an extraction rate that approached the theoretical maximum.

5.4.4. Production of Lutein and β-Carotene

Lutein, a beneficial natural pigment and antioxidant, is extensively utilized in the realms of food additives, pharmaceuticals, and animal feed [105]. Peng et al. [106] extracted lutein from silkworm excrement using 95% ethanol and petroleum ether as solvents, achieving a yield of 0.4%. β-carotene is a fat-soluble provitamin A with various physiological functions, including antioxidant properties and the ability to enhance an organism’s resistance [107]. Lin et al. [108] developed a process flow for β-carotene extraction from silkworm excrement: pretreatment → acetone extraction → saponification → petroleum ether extraction → column chromatography purification → recrystallization and refinement. Additionally, a high-performance liquid chromatography (HPLC) method was established to simultaneously determine lutein and β-carotene content in silkworm excrement, with the extraction conditions being optimized through an orthogonal test [109].

5.4.5. Preparation of Corrosion/Scale Inhibitors

Guo et al. [110] utilized acetone as the solvent and conducted extraction from silkworm excrement in a water bath at 60 °C. The extract was concentrated to yield a paste, which was subsequently treated with glacial acetic acid to remove magnesium ions, ultimately yielding pheophytin. As an efficient and enduring green corrosion inhibitor, pheophytin provided 93.97% inhibition efficiency against copper at a concentration of 0.1 g/L. Liu et al. [111] discovered that silkworm excrement extract inhibited calcium scale formation by chelating or adsorbing calcium ions, altering the calcium carbonate crystal form from calcite to spherulite, and exhibiting its superior corrosion inhibition properties in brine by forming a protective film on the steel surface.

5.4.6. Production of Other Products by Easy Extraction

Silkworm excrement can also be utilized to produce novel cosmetics, dyes, and cigarette additives. Lee et al. [112] found that silkworm excrement extract was able to inhibit α-MSH-induced melanin synthesis partially, demonstrating a significant depigmentation effect in a zebrafish model and providing a scientific basis for the development of novel health and cosmetic applications. Studies have indicated that pyrrole chlorophyll and carotenoids present in silkworm excrement can bond with amino acids in protein fibers at a pH level of 4.8, resulting in a dark green–brown coloration and superior colorfastness of the fabric. The fabric dyed with silkworm excrement exhibits exceptional UV protection and antioxidant properties [113]. Moreover, Cheng et al. found that the extract from silkworm excrement could effectively enhance the sweetness of cigarette smoke, soften its texture, and improve the aftertaste [114].

5.4.7. Production of Other High-Value Substances Such as Microbial Carbon Source

As a microbial carbon source, silkworm excrement can also be utilized to produce PHBV and pectinase. PHBV is a biodegradable polyester that can be synthesized by microorganisms. Cai et al. [115] utilized waste silkworm excrement as a carbon source to produce PHBV with a high 3-hydroxyvalerate content through open fermentation by Haloferax mediterranei, which further reduced the cost of PHBV production. For another, pectinases are mixed enzymes that break down pectic substances and hold significant importance across various industries, including food, textiles, beverages, pulp and paper, and biofuels [116]. Pectinase could also be produced by fermenting silkworm excrement with Aspergillus niger, and the pectinase activity was measured to be 15.08 U/mL [117].

5.5. Materials

Given the unique material structure of silkworm excrement, it can be utilized to produce various biochar materials, including adsorbents, electrode/capacitor materials, sensing devices, and biomedical applications (Figure 4). Current research on its materialization primarily focuses on adsorbents, electrodes/capacitors, and sensing materials, while studies on using silkworm excrement to prepare biomaterials remain relatively limited. Moreover, many materials are still in laboratory stages, and further research is needed to achieve practical applications.

5.5.1. Adsorption Materials

Utilizing the unique microstructure of silkworm excrement, a variety of biochar-based materials can be crafted. Wu et al. [17] developed a novel porous carbon composite (Fe@C) from silkworm excrement that demonstrated exceptional selectivity and adsorption capacity for separating a 4-methylanisole/4-anisaldehyde mixture. Yang et al. [118] created a biochar with an outstanding pore structure and a high degree of graphitization by employing KOH activation on silkworm excrement, which significantly improved Cd²⁺ adsorption performance. Additionally, high–specific surface area activated carbon–silica composites were produced using a microwave-assisted KOH activation method, exhibiting remarkable adsorption and supercapacitor capabilities [40,119]. In the same year, a bioporous carbon material (BCSE) with a meso-microporous structure was synthesized from silkworm excrement. Investigations into its cooperative adsorption, slow-release performance, and thermal stability of monosultap and dinotefuran provided an experimental foundation for the efficient utilization of multi-component pesticides on biochar [38]. The adsorption materials can be further applied to the treatment of environmental issues, such as heavy metal pollution and organic pollutant remediation, which will be discussed later.

5.5.2. Electrode/Capacitor Materials

A nanocomposite of MnO₂/biomass carbon, based on silkworm excrement, could be synthesized through a simple hydrothermal reaction. It demonstrated high specific capacitance and excellent cycling stability in high-performance supercapacitors [120]. In the same year, Hu et al. [121] produced a porous carbon material, SEPC, derived from silkworm excrement using a one-step metal-catalyzed cracking method. They then created a composite, SEPC-PbO, by combining and calcining SEPC with desulfurized waste lead paste. This composite was utilized as an anode additive for lead-acid batteries, substantially enhancing the batteries’ cycle life and sulfation resistance. Wu et al. [122] developed a silkworm excrement biomass carbon-based composite material to inhibit the polysulfide shuttle effect. This was achieved through mechanisms of physical adsorption, chemical adsorption, and catalytic conversion, which can markedly improve the performance of lithium–sulfur batteries. Jiang et al. [123] engineered a multifunctional and sandwich structural material (SC@CoS₂), which is composed of silkworm excrement-derived porous carbon loaded with nanoscale CoS₂ particles. This structure was employed in high-performance lithium–sulfur batteries to suppress the polysulfide shuttling effect and to improve the batteries’ cycle stability and energy density.

5.5.3. Sensing Materials

BU et al. [124] developed a method to prepare carbon dots through high-temperature direct carbonization or the hydrothermal method, utilizing silkworm excrement as a carbon source. They characterized these carbon dots, revealing that they possess excellent fluorescence properties and potential for selective detection of heavy metal ions such as Cd²⁺ and Pb²⁺. Lu et al. [125] reported the creation of nitrogen-doped carbon nanoparticles (N-CNPs) from silkworm excrement via a hydrothermal method, which were applied to design an “on–off–on” fluorescent sensor for the detection of Fe (III) and biothiols. In the research by Huang et al. [126], nitrogen- and sulfur-modified carbon quantum dots with a uniform particle size distribution and excellent luminescence properties were successfully synthesized from silkworm excrement using microwave synthesis. The carbon quantum dot materials prepared from silkworm excrement show broad application prospects in bio-detection and imaging, particularly in the highly selective detection of metal ions such as Cu²⁺. Mu et al. [127] developed a high-strength, frost-resistant, and electrically conductive dual physico-chemical crosslinked hydrogel based on silkworm excrement cellulose, suitable for pressure sensing in low-temperature environments. Xu et al. [128] utilized silkworm excrement to prepare microporous carbon (SEMC) and combined it with SnO₂ nanoparticles to construct a composite structure, resulting in a glycol gas sensor with high sensitivity, high performance, excellent selectivity, and long-term stability.

5.5.4. Biomedical Materials

Bao et al. [129] have utilized silkworm excrement as raw material to make red-emissive carbon dots (SCDs) with photodynamic therapy functionality. This was achieved through a “top–down” approach, followed by a series of processes including Cu doping. Eventually, they developed a novel nanomedicine, HF-SCDs@Cu. This nanomedicine combines ferroptosis, photodynamic therapy, and oxygen generation capacity to effectively reverse the tumor immunosuppressive microenvironment and enhance PD-L1-mediated immune checkpoint blockade therapy.

5.6. Environmental Protection

The use of silkworm excrement also aids in environmental conservation. Recent studies have shown that these waste products can be utilized to treat heavy metal pollution, manage herbicide contamination, and control antibiotic pollution. By fermenting silkworm excrement to generate biogas, we can diminish the consumption of fossil fuels. Furthermore, employing silkworm excrement as an organic fertilizer helps to lower agricultural carbon emissions (Figure 5). Nevertheless, current research on the life cycle assessment of silkworm excrement as organic fertilizers is still in its infancy, with the comprehensive environmental impact—including energy consumption during processing, transportation, and possible secondary emissions—often being neglected.

5.6.1. Treatment of Heavy Metal Pollution

One of the significant issues in current environmental governance is heavy metal pollution, particularly severe near mining areas [130,131]. The literature reports that silkworm excrement can effectively passivate heavy metal-contaminated soil [132]. Specifically, a mixture of silkworm excrement and bentonite clay at a ratio of 4:1 demonstrates enhanced passivation efficacy. At an addition rate of 0.5%, the effective immobilization rates of cadmium (Cd) and zinc (Zn) reach 24.9% and 30.5%, respectively [133]. Building on this research, a practical recycling technology has been proposed: “planting mulberry trees (and other plants) in heavily heavy metal-polluted soils near mining areas → harvesting mulberry leaves to feed silkworms → using silkworm excrement to restore the local environment, including vegetation and soil bacterial communities.” The application of this technology not only helps reduce the bioavailability of soil heavy metals but also significantly promotes plant growth and soil microbial ecological recovery [130].

Biochar-based materials derived from silkworm excrement can also manage heavy metal pollution [134]. According to Bian et al. [135], a novel functionalized biochar (GBC) was successfully produced from silkworm excrement, enhancing the removal of Pb and Cd from industrial wastewater by approximately 12% and Cu by about 94.6% compared to the original biochar (BC). Similarly, Peng et al. [136] created a novel composite material, SiO₂NPs@BC (SBC), by combining silica nanoparticles (SiO₂NPs) with silkworm excrement biochar, which is effective for removing Cd from wastewater and mitigating Cd contamination in soil. However, Zang et al. [137] found that silkworm excrement biochar (SEB) plays a dual role in soils co-polluted with Cadmium (Cd) and Arsenic (As): on the one hand, SEB significantly reduces the bioavailability of Cd and promotes its conversion into a stabilized form by increasing soil pH (up to 10.08), while on the other hand, the high alkalinity of SEB activates As, leading to an increase in the water-soluble and exchangeable states of As in the soil.

5.6.2. Management of Herbicide Pollution

Herbicides, widely used in agriculture, are also a pollutant that cannot be overlooked [138]. Huang et al. [48] indicated that herbicide pollution substantially suppresses soil microbial activity, diversity, and community structure. Their study further demonstrated that silkworm excrement could enhance microbial biomass carbon by 41.60%, dehydrogenase activity by 503.97%, and catalase activity by 78.26% in herbicide-contaminated soil, proving beneficial for the remediation of such soil. Additionally, silkworm excrement could be utilized as a carrier for herbicide-degrading bacteria, facilitating the remediation of herbicide-contaminated soil. A composite material was developed to efficiently remove diuron from contaminated soil by immobilizing Arthrobacter globiformis D47 on a silkworm excrement carrier. This composite exhibited exceptional degradability and stability in laboratory and field tests, significantly reducing the diuron’s half-life period to 7.69 days [139].

5.6.3. Control of Antibiotic Pollution

Antibiotic pollution poses a serious threat to both the ecological environment and human health [140]. Zhou et al. [141] successfully prepared biochar-based iron–cobalt doped carbonitride composites from silkworm excrement, which significantly increased the specific surface area and pore volume. These composites exhibited highly efficient removal performance for tetracycline in the persulfate activation system. Raoultella ornithinolytica CT3, a strain of bacteria capable of efficiently degrading chloramphenicol, was isolated and identified from silkworm excrement. Moreover, nine new intermediate metabolites for chloramphenicol biotransformation were reported for the first time. Toxicity assessment revealed that the final metabolites were harmless to the environment, demonstrating the potential of CT3 to remove chloramphenicol from the environment [142].

5.6.4. Reducing Carbon Emissions

One of the significant sources of carbon dioxide in the atmosphere is fossil fuels [143]. Silkworm excrement can be utilized for fermentation to generate biogas, a clean energy source, thereby decreasing reliance on fossil fuels and lowering carbon emissions. Zhou et al. [34] discovered that when properly pretreated, silkworm excrement can serve as an alternative to pig manure as a feedstock for household biogas digesters. This allows for successful initiation and ensures stable daily operation. Luo Hongyan et al. [144] determined that the feedstock ratio and pH were critical factors influencing the biogas fermentation of silkworm excrement through an orthogonal experimental design method. They optimized the fermentation parameters, such as a silkworm excrement to pig manure ratio of 1:1, a pH of 6.5, and a substrate concentration ranging from 6% to 10%. These adjustments notably enhanced gas production and methane content.

The carbon emissions produced during agricultural activities are significant and cannot be overlooked [145]. It is estimated that China’s total agricultural carbon emissions were approximately 260,919,400 tons in 2022 alone [146]. Interestingly, silkworm excrement, as an agricultural waste, contributes to reducing carbon emissions during agricultural production. Liu et al. [147] found that using silkworm excrement organic fertilizer in conjunction with chemical fertilizers increased the organic carbon content of paddy soil and effectively reduced CO₂ emissions by about 15.1%.

6. Summary and Prospects

As a sustainable and valuable resource, silkworm excrement holds promise for comprehensive utilization. The resource is immense in production, low in cost, and unique in structure, containing a wealth of chemical and microbial components. This makes silkworm excrement a potential candidate for a variety of applications. As feed, silkworm excrement provides numerous benefits, including rich nutritional value, the ability to enhance animal immunity, promote growth, and improve the quality of animal products while remaining cost-effective. When used as fertilizer, it improves soil properties, encourages the healthy growth of crops, and contributes to food security. It enhances soil enzyme activity, increases nutrient content, boosts microbial diversity, reduces the bioavailable content of heavy metals in the soil, and diminishes heavy metal accumulation in crops. Silkworm excrement is also extensively utilized in the medical field, where it has shown efficacy in treating conditions such as insomnia, diabetes, cancer, anemia, migraines, and arthritis. In the chemical industry, silkworm excrement can be employed to produce chlorophyll, corrosion inhibitors, pectin, flavonoids, lutein, β-carotene, and other high-value products. Additionally, it serves as a cost-effective microbial carbon source for producing other high-value substances. In the materials sector, silkworm excrement can be used to prepare adsorption materials, electrode/capacitor materials, sensing materials, and biomedical materials, demonstrating its broad range of applications. In environmental protection, silkworm excrement is utilized to treat soil heavy metal pollution and to remove heavy metals, herbicides, and antibiotics from industrial wastewater or soil. Furthermore, its fermentation can produce biogas or serve as a fertilizer, aiding in carbon reduction.

Research into the comprehensive utilization of silkworm excrement resources exhibits a certain degree of diversification. The application of silkworm excrement in medicine, the chemical industry, materials, and environmental protection has garnered significant attention, particularly. Nonetheless, research on the toxic side effects of silkworm excrement remains insufficient, and the key therapeutic targets for specific diseases and their regulatory mechanisms still require further investigation and experimental validation. Many advanced biotechnologies, such as supercritical fluid extraction technology, have yet to be applied to the silkworm excrement extraction process. The use of silkworm excrement as a microbial carbon source for large-scale factory fermentation has not yet been realized, and there are few studies on the production of high value substances by fermentation of silkworm excrement. In the future, the fermentation process of silkworm excrement needs to be further developed and optimized. The applications of silkworm excrement in material preparation and environmental protection remain at the laboratory scale, and further research is needed to achieve practical applications. As the technology for the comprehensive utilization of silkworm excrement continues to advance and awareness of sustainable development and resource recycling grows, we are confident that this previously underutilized resource will be further developed and widely applied in various aspects of human life.