Ouch - Chemical Defense in Insecta

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  Today, I sat upon the beach below Au Sable’s campus. The muddy lake water below the skewed, brittle dock was like glass, reflecting the soles of the redwing boots my grandfather had given to me last summer. The weather I felt on my skin was balmy, the sky above me was blue, and the hotdogs I was happily consuming were crisp, smoky, and quite perfect. I was at peace with a world I was sure was full of joy, happiness, and benevolence towards all men. How wrong I was. As I lay in my restive repose, participating in my porcine feast, my peace and goodwill erupted into pain and grief, for a small bug, possibly an insect of the order Coleoptera, flew with a steely and malignant purpose into my vulnerable and unwitting right ocular implement. With surprise and slight alarm, I flinched. I blinked. I rubbed my orb-shaped organ. Horror and catastrophe! For this action unleashed the most unimaginably painful burning sensation, coating my eyeball immediately in its hellish excruciation. As I write, visually impaired and slightly wiser about my hotdog eating habits, I have a theory. Perhaps my misadventure was an up close and personal demonstration of chemical defense strategies used by insects. What is chemical defense? It is used by a wide range of insect orders and families, from larval Lepidoptera to adult Coleoptera. As such, It comes in many shapes and forms, differing in both its implementation and its function. Chemical defenses can come from excretion, secretion, reflex bleeding, and injection. Excretion can come from specially designed exocrine glands, which produce chemical toxins, or from glands called osmeteria. Found on the swallowtail caterpillar, osmeterium are organs that emerge from the thorax behind the head of the caterpillar when threatened. These organs excrete a special chemical defense that drives away ant predators.

Illustration of the Osmeterium (via Ask An Entemologist)


Defenses can also be secreted; some members of the order Blattodea secrete defenses from the anus to prevent predation. Members of the order Lepidoptera secrete chemicals onto special urticating hairs to cause irritation in predators. Reflex bleeding is another fascinating type of defense - Blister beetles can voluntarily release their hemolymph from joints in their legs, which contains potent chemicals. Finally, chemical defenses can be released via a sting - bees, wasps, and other members of Hymenoptera have a stinger on their abdomen that can release venom, either as a defense or a predatory function. Chemical defenses, implemented in diverse ways, also have different functions. The chemicals produced by insects can repel, cause damage, or incapacitate. Stink bugs (order Hemiptera) secrete an unpleasant smell that makes them unappetizing to potential predators. This simple repulsive act is not the most severe defense; the bombardier beetle (order Coleoptera) excretes two chemicals from separate glands in their bodies, which form a hypergolic reaction to produce a hot blast of hydroquinone mixed with hydrogen peroxide. This blast is highly dangerous, and is a potent defense against attackers.


Hypergolic reaction of a Bombardier Beetle (via MIT News)

Other bugs simply incapacitate their predators, using glue like substances or irritants that cause attackers to leave them be. The incredible deterrents that insects have adapted to produce, while painful for larger predators and threats like my eyeball, are incredible to consider. Not only can bugs defend themselves with chemicals produced by their own bodies, but they can burn, blister, glue, and stink up enemies with these chemicals. They can do these things using glands, special organs, and even their own blood. The diversity with which they manifest are further proof of the wonderful and complex world that God created. So next time you find yourself sitting upon a dock on a Michigan glacial lake in the summer, remember to first consider the dangers of such an action presented by bugs and their defensive chemicals. 


https://genent.cals.ncsu.edu/bug-bytes/defense/

https://www.thecaterpillarlab.org/single-post/2016-1-6-spotlight-on-caterpillar-anatomy-the-osmeterium

https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Bombardier-Beetles

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