If Noah’s Ark was home to two examples from every animal species on Earth, one-quarter of its passengers would have been beetles: Coleoptera. The order Coleoptera is the most diversified of all those on the living planet. It brings together over 400,000 known species, and the list gets longer every year. These exceptional insects are found in almost every type of habitat. For example, in Alaska, certain larvae of the genus Cucujus can survive at temperatures as cold as-150°C, whereas other Coleoptera (e.g., Onymacris sp., the desert darkling beetle) survive on the minimal humidity present in the arid air of the Namibian deserts. Coleoptera have taken advantage of a number of types of food sources to prosper. Some species are formidable predators, while others pollinate flowers by grazing on nectar and pollen. Some feed on feces, animal cadavers, fungi or wood.
A precious legacy
Stag beetles (Lucanidae), a family of coleoptera distinguished by oversized mandibles in male adults (figure 1), are saproxylic, meaning they need decomposing wood for their development. Like all Coleoptera, stag beetles are holometabolic: from every egg laid a larva will hatch (figure 2), which changes into a pupa before finally emerging as an adult. It’s more precisely these larvae that use wood as a food source. Unfortunately, it’s impossible for stag beetle larvae to eat and digest the cellulose and lignin that protect the cells of a piece of healthy wood. They need the help of wood-eating fungi, which break wood down by way of their specialized enzymes. The hyphae (figure 3) of those fungi penetrate and break wood down and make it digestible for the beetle. Additionally, in eating the shell of their egg after they hatch, the larvae receive a precious legacy left by their mother: a digestive flora of yeasts and bacteria that will enable them to extract even more nutrients from the decomposing wood they ingest. Stag beetles, in other words, wouldn’t be able to feed themselves without the help of these fungi!
Montreal stag beetles
The team at the Insectarium de Montréal is currently raising a small brightly colored species of stag beetle called Lamprima adolphinae. Again, the larvae of this beetle (which hails from New Guinea) are saproxylic; but the thing is, it’s extremely difficult to find pieces of wood colonized by wood-eating fungi in the middle of Montreal. Insectarium technicians are therefore initiating the decomposition of logs themselves courtesy of techniques borrowed from mycology! Different species of oyster mushrooms are inoculated in bags filled with sawdust. When the bags are completely colonized by the mycelium of the fungi, all that’s left is to add the young larvae. These tunnel inside the bags and feed on the wood colonized by the mycelium. In barely two months of development on this super-diet, the Lamprima larvae grow tremendously in size and turn into pupae, and then into spectacular adults.
You’ll be able to admire the Lamprima adolphinae’s impressive metallic luster as well as a host of other insects and arthropods when the new Insectarium opens in the summer of 2021. A rendezvous you won’t want to miss!
- Abdel-Hamid, A. M., Solbiati, J. O., et Cann, I. K. (2013). Insights into lignin degradation and its potential industrial applications. In Advances in Applied Microbiology (Vol. 82, pp. 1-28). Academic Press.
- Bouchard, P. (2014). The Book of Beetles: A Life-Size Guide to Six Hundred of Nature's Gems. University of Chicago Press.
- Geib, S. M., Filley, T. R., Hatcher, P. G., Hoover, K., Carlson, J. E., del Mar Jimenez-Gasco, M., ... et Tien, M. (2008). Lignin degradation in wood-feeding insects. Proceedings of the National Academy of Sciences, 105(35), 12932-12937.
- Parker, A. R., et Lawrence, C. R. (2001). Water capture by a desert beetle. Nature, 414(6859), 33.
- Sformo, T., Walters, K., Jeannet, K., Wowk, B., Fahy, G. M., Barnes, B. M., et Duman, J. G. (2010). Deep supercooling, vitrification and limited survival to–100 C in the Alaskan beetle Cucujus clavipes puniceus (Coleoptera: Cucujidae) larvae. Journal of Experimental Biology, 213(3), 502-509.
- Slaytor, M. (1992). Cellulose digestion in termites and cockroaches: what role do symbionts play?. Comparative Biochemistry and Physiology Part B: Comparative Biochemistry, 103(4), 775-784.
- Tanahashi, M., Kubota, K., Matsushita, N., et Togashi, K. (2010). Discovery of mycangia and the associated xylose-fermenting yeasts in stag beetles (Coleoptera: Lucanidae). Naturwissenschaften, 97(3), 311-317.
- Tanahashi, M., Matsushita, N., et Togashi, K. (2009). Are stag beetles fungivorous?. Journal of insect physiology, 55(11), 983-988.