Creepy crawling chemists may surprise the unwary

By Gary Raham
Nature Writer and Illustrator

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While some people may stomp first and ask questions later when it comes to "bugs" of various sorts, others seem naturally drawn to observing-- and perhaps sniffing--creatures of the creepy crawling variety.

Entomologist Thomas Eisner falls into the bug-loving (entomophile) and bug-sniffing (odorophile?) category. Over a long career, highlighted in the book "For Love of Insects," he tells how his fascination with both insects and chemistry has lead him to some amazing discoveries.

Take bombardier beetles, for example, which are members of the ground beetle family (Carabidae). Most beetles in this group are black and shiny with long legs and easy to spot when lifting a rock or weeding the garden. Nearly everyone has encountered "stink bugs," other members of this family that, when handled too vigorously, emit the slightly nauseating odor of overripe cheese. Bombardiers (genus Brachinus) are more colorful than many carabids, with reddish yellow legs and hard external wings (elytra) that wink with bluish to black iridescence. They also go one step further in the chemical warfare department by shooting off rounds of hot noxious chemicals from their rear ends, which are often elevated like cannons in the direction of an aggressor.

Entomophiles like Eisner take cannon fire as a challenge rather than a reason to run for cover. Over several field and laboratory seasons, Eisner and colleagues were able to piece together the bombardier's story and the nature of its chemical arsenal.

The beetle possesses glands that produce a mixture of hydroquinones and hydrogen peroxide. These latter chemicals travel to two large reservoirs at the rear of the animal's abdomen. These reservoirs are flexible sacks connected to a more rigid "reaction chamber" that is isolated by a valve. When the beetle gets upset, say when a frog flicks out its sticky tongue, it contracts muscles that squeeze the reservoirs and force their contents into the reaction chamber. Enzymes enter the chamber, converting the hydroquinones and hydrogen peroxide to oxygen, benzoquinone, water and heat. The oxygen forces the hot mixture out with audible "pops." The beetle can also aim its cannon with amazing accuracy, spraying directly toward a leg that might get pinched by a predator.

Benzoquinone chemistry, it turns out, is a favorite of many species, including certain millipedes and "daddy longlegs." The odor is pungent and may stain your hands brown.

But the chemical magic of insects doesn't end there. Some ants, for example, can produce terpenes, the same kind of defensive chemicals produced by pine trees (and that gives them their distinctive smell) and used in the production of turpentine. Other ants produce acid deterrents, most notably formic acid.

Other acid-producing creatures include the desert-dwelling whip scorpion, which does resemble a scorpion with a long whiplike feeler on its rear end. A knob at the base of this feeler is actually a revolving "gun turret" that shoots a mixture that is 84 percent acetic acid, or vinegar. It's no wonder that these whip scorpions are commonly called vinegaroons. Eisner found that the whip scorpion could easily discourage ants, grasshopper mice, lizards, birds and armadillos with its spray - one reason this species has been around for some 300 million years.

Mystery lovers know that cyanide is a favorite poison for murders. It smells like bitter almonds, a plant source of the compound. Arthropods, including some millipedes, centipedes, beetle larvae and moths can brew up this poison, too. The cyanide is bound up with an aldehyde and sugar in a compound that can be stored safely in one chamber, then mixed with enzymes in another chamber that unbinds the cyanide during stressful encounters with ants, toads and other enemies.

Perhaps one of the strangest chemical defenses Eisner discovered was a walking stick that shoots out spray filled with catnip. Walking sticks are bizarre-looking insects that attempt to resemble a twig in the hopes that their predators--usually birds--are not paying close attention. If that fails, however, they shoot out catnip (also known as nepetalactone), which birds and many insects find much less appealing than a cat does. Catnip is usually prepared from a mint, which also produces the compound.

You may have noticed a theme here. Plants and a variety of arthropods have developed much the same weaponry for much the same reason: defense against getting eaten. This is powerful motivation for becoming a creative chemist - much more motivation than you may have had for studying chemistry in school. If your interest in chemistry (and creepy crawlers) has improved since then, you will find Eisner's book a fascinating read.

Reference: Eisner, Thomas. "For Love of Insects." Cambridge, Mass.: The Belknap Press of Harvard University Press, 2003.