Meet the ballistics experts of the bug world: A quick draw beetle that fires volatile liquids with the pulse of a Tommy Gun, aphids that self-combust at the threat of a predator and a double-pistoled worm that sprays its victim with streams of goo. Of course, these insects are not the only invertebrates carrying chemical artillery—bees are maybe the most famous projectile-launching bugs around. The below insects, however, give a unique look into chemical warfare on a small scale.
The African bombardier beetle produces and stores hydroquinone and hydrogen peroxide in two separate reservoirs in its abdomen. When the right moment arrives, say an ultra-curious ant approaches, the beetle releases both chemicals into an explosion chamber containing water and catalytic enzymes. The breakdown of the noxious chemicals creates an excess of oxygen and heats up the liquids to beyond the boiling point.
According to the book Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals by Ross Piper, the resulting oxygen and vapors build up, the one-way entry point to the explosion chamber shuts off and the cocktail is launched through a small opening in the tip of the beetle’s abdomen—all occurring in a fraction of a second. The chamber fills again, reacts, the valve closes and the chemicals explode once more, a process that can lead to a series of about 70 explosions and the appearance of a pulsating stream. The noxious, boiling hot chemicals are released with audible pops, searing the predator and forcing it to retreat; the beetle has even been known to burn humans who handle it (see above video).
The African bombardier beetle is unique from other bombardier beetles due to its accuracy—a revolving turret fires the cocktail with a 270 degree range. A study published in Proceedings of the National Academy of Sciences in 1999 showed the remarkable accuracy of these beetles. Researchers pinched specific regions of the beetles’ limbs, prompting it to aim at hard-to-reach areas. The beetles were able to hit the specific spots the researchers pinched regardless of the extreme angles.
Cabbage aphids are another species of chemists. These self-sacrificing aphids are willing to detonate at the sight of a predator if it means protecting the rest of the colony. According to a 2007 study in Proceedings of the Royal Society: Biological Sciences, cabbage aphids use chemicals ingested from the plants they eat—specifically, they acquire glucosinolates from cruciferous vegetables such as the mustard plant.
The aphids are born with an enzyme, stored in the muscles of the head and thorax, to breakdown these glucosinolates if the time ever comes. With the bite from a predator, for example, blood rushes to the muscle and the reaction causes the aphid to combust instantaneously, releasing the toxin on the predator and effectively preventing it from moving toward the rest of the colony.
The velvet worm Onychophora shares a common ancestry with both annelids and anthropods and is native to tropical climates. What likely started off as a defense mechanism evolved into the primary means of hunting prey: Velvet worms are equipped with a pair of slime glands located below their antenna. These modified limbs squirt a stringy goo that captures predators or prey in the process (see above video in Spanish). Among proteins and lipids, the composition of this slime is unique to velvet worms. According to a 1999 study, one substance called nonylphenol—an organic compound found in some detergents and pesticides—is only naturally produced by velvet worms.
What is equally impressive about velvet worms is their method of reproduction, which ranges from egg-laying to live-bearing depending on the species. Some species have ovipositors, others have penis-like structures. In the species Euperipatoides rowelli, males collect sperm on their heads, and when a female is encountered, insert the head into the female’s vagina. And the seemingly all-female species Epiperipatus imthurni from Trinidad, which has no reported sightings of males, reproduce by parthenogenesis.
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Eisner, T. (1999). Spray aiming in the bombardier beetle: Photographic evidence Proceedings of the National Academy of Sciences, 96 (17), 9705-9709 DOI: 10.1073/pnas.96.17.9705
Kazana, E., Pope, T., Tibbles, L., Bridges, M., Pickett, J., Bones, A., Powell, G., & Rossiter, J. (2007). The cabbage aphid: a walking mustard oil bomb Proceedings of the Royal Society B: Biological Sciences, 274 (1623), 2271-2277 DOI: 10.1098/rspb.2007.0237
Benkendorff, K., Beardmore, K., Gooley, A., Packer, N., & Tait, N. (1999). Characterisation of the slime gland secretion from the peripatus, Euperipatoides kanangrensis (Onychophora: Peripatopsidae) Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 124 (4), 457-465 DOI: 10.1016/S0305-0491(99)00145-5