Secret Weapons:
Defenses of Insects, Spiders, Scorpions, and Other Many-Legged Creatures

Thomas Eisner, Maria Eisner + Melody Siegler

Harvard University Press 2005
A book review by Danny Yee © 2007
Each of the seventy chapters in Secret Weapons is named after a species, but they often survey the order or class more broadly, and in some cases touch on related aspects in unrelated species. The chapter on the Carpenter Ant Camponotus floridanus, for example, is actually a very brief survey of defenses in ants generally. The emphasis is on chemical defenses, but extends to mechanical defenses, camouflage, and the behaviours which are linked to defenses.

The chapters are too brief to go into details and just give an outline of a few key defense systems. Each has colour photographs illustrating key behaviours, structural formulae for the chemicals involved, and full references. To give a feel for this, here is one of the shortest chapters:

Family Chrysopidae
Ceraeochrysa smithi
A green lacewing
Insects of the family Chrysopidae, the green lacewings, have the remarkable habit of laying their eggs on stalks. To produce an egg, the female first applies a droplet of clear gelatinous fluid from the tip of the abdomen to the substrate. She then flexes the abdomen abruptly upward, so as to pull the droplet into a thread and, after pausing briefly, squeezes out the egg. Thread-hardening occurs quickly, before the egg is entirely extruded. Chrysopids lay their eggs singly or in batches, and sometimes even in tight clusters with the stalks bundled together.
Ants are predators of chrysopids, and will if they can ascend a stalk, cut the egg free with their mandibles, and carry it away. One chrysopid, Ceraeochrysa smithi, has a way of keeping ants off the stalks. It coats the stalks with droplets of an oily secretion that is powerfully repellent to ants. Chemical analyses showed the fluid to consist of a mixture of long-chain fatty acids, including oleic acid; a fatty acid ester, isopropyl myristate; and a series of saturated aldehydes, including butanal, decanal, and pentadecanal.
The young larvae, when they emerge from the egg, have the problem of avoiding bodily contact with the oil when they descend along the stalk. They deal with the problem by ingesting the fluid. They pause by each droplet as they come down and suck it up with their hollow, sickle-shaped jaws. Upon arrival at the base of the stalk, they briskly walk away, to commence their lives as hunters.
One other chrysopid species, Leucochrysa floridana, also coats its egg stalks with a deterrent fluid. Preliminary work has shown this fluid to differ chemically from that of C. smithi.

Accompanying this text are chemical structure diagrams for the five compounds mentioned, publication details for the source paper in Proceedings of the National Academy of Sciences, and three photographs.

"Left: The egg of an unidentified chrysopid, borne on a stalk devoid of oil droplets, as is typical for most chrysopid species. Middle: an egg of Ceraeochrysa smithi, on its oil-beset stalk. Right: A newly emerged larva of C. smithi descending the egg stalk and imbibing the oil droplets."

Secret Weapons covers much the same material to Eisner's For Love of Insects, but in a rather different fashion. It lacks any "popular" biographical, travel, and historical material and it includes technical chemical structure diagrams and full references. With such short chapters, however, there's no room to go into any depth, and where there's a direct overlap Secret Weapons often has less detail than For Love of Insects.

The approach in Secret Weapons will be useful for entomologists or chemists wanting a survey of insect defense systems; they can go to the technical literature for the details. It will also appeal to generalists who just want a broad summary overview. And an appendix offers twelve pages on "How to Study Insects and Their Kin", aimed at amateur collectors and experimentalists.

April 2007

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%T Secret Weapons
%S Defenses of Insects, Spiders, Scorpions, and Other Many-Legged Creatures
%A Eisner, Thomas
%A Eisner, Maria
%A Siegler, Melody
%I Harvard University Press
%D 2005
%O paperback, references, index
%G ISBN 0674024036
%P 372pp