**1. Introduction**

The characteristics that define a healthy environment have changed significantly over human history. The Miasma Theory (400 BC), an obsolete scientific theory, suggested that diseases are caused by bad air [1]. Later, the discovery of germs [2,3] as the origin of diseases led to a public perception of all microbes as pathogenic. As a result, humans' indoor lifestyle and their yearning for hygiene have set the goals for the design of buildings, and criteria for the selection of materials for isolation. In addition, human activities, e.g., monocultures and intensified agriculture, caused the isolation of other living species from their coevolved symbionts, e.g., through habitat fragmentation. A significant "dewilding" activity is the exploitative domestication of wild animals, especially keystone species like honeybees [4].

Among other pollinators, honeybees play a crucial role in conserving biodiversity in flora and fauna. Besides that, they ensure food diversity for human society. Commercial honeybees used in agriculture are affected by a rich spectrum of stressors, such as overcrowded positioning or long-range transportation of hives, and agriculturally applied chemicals. Honey and other bee products crucial to honeybees' wellbeing are also removed from honeybee colonies. In the meanwhile, cities are becoming megacities due to human population growth. This comes at the expense of diminishing forests, marshlands, and other ecologically vital habitats. Finally, several essential habitat types are decreasing, directly and indirectly harming all bee species. All of these interventions have a significant

**Citation:** Ilgun, A.; Schmickl, T. Mycelial Beehives of HIVEOPOLIS: Designing and Building Therapeutic Inner Nest Environments for Honeybees. *Biomimetics* **2022**, *7*, 75. https://doi.org/10.3390/ biomimetics7020075

Academic Editors: Andrew Adamatzky, Han A.B. Wösten and Phil Ayres

Received: 15 March 2022 Accepted: 26 May 2022 Published: 7 June 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

impact on honeybees' indoor lifestyle by limiting the diversity of microorganisms within hive interiors and, as a result, the likelihood of symbiotic connections occurring.

Symbiosis is a commonplace relationship of microbial and host elements working together to ensure good nutrition, health, and resistance [5]. When it comes to living in harmony with microorganisms, social insects are excellent models [6]. Among many microorganisms, fungi are one of the key actors within the insect microbiota. Fungi and insects have coevolved a wide array of functional interactions over the past 400 million years [7]. Fungal volatiles, which play an important role in terrestrial ecosystems, also affect the nesting and reproductive behaviour of insects [8,9]. Many termite species actively cultivate fungus to digest the foraged organic materials that they cannot digest themselves internally. The fungus then becomes digestible food for the insects. For this natural form of agriculture, they also build specific rooms in their nests, where the fungus can grow and thrive, forming a prominent form of fungus–insect symbiosis [10]. Humans do not interact with their built environment as effectively as other social animals do. Humans' architectural product is one that provides some degree of isolation and protection from the "outside" world. It artificially frames human activity [11]. While in other ecosystems, habitats which can support the social lifestyle of animals are inherently permeable to the outside world. Still, the contemporary bio-inclusive architectures propose mechanisms to incorporate other lifeforms into the outer layers of building boundaries. This, once again, separates the wildlife from the human population inside living spaces and does not support the potential health benefits the other life forms have on indoor city dwellers [12–14]. Modern beehives are an example of manmade design thinking being imposed on the habitats of other living animals. In general, artificial habitats, such as beehives and human houses, pose challenges in designing how forms, spatial configurations, and materials can affect the microbial diversity that establishes itself in those artificial environments.
