Bombardier beetles deploy 500 pulse per second chemical cannons, which they can fire in all directions and accurately target against attacks on different parts of their bodies.
"The bombardier is even able to fire forward over its back. It does this by bouncing the spray off a pair of skeletal reflectors that it manages to stick out from the tip of the abdomen at the moment of ejection. Ants are therefore at risk even if they scale a beetle's back."
Whip scorpions spray a mix of acetic and caprylic acids. Millipedes and a range of insects produce hydrogen cyanide. One way to manage poisonous substances in high concentrations is by mixing separately produced precursors "on demand"; another is by storage and transport in drainage tubes lined with cuticle.
Polyxenid millipedes use "grappling hook" bristles to entangle ants. When attacked, Hemisphaerota cyanea beetles hunker down and hang on with an adhesive force hundreds of times their body weight; this stops ants but not specialised predators that inject muscle relaxants. And there are caterpillars that consume Drosera sundews, using sensory hairs to carefully manoeuvre around the sticky droplets.
Photinus fireflies use lucibufagins for defence and female Photuris fireflies use mimicry to catch Photinus males, from which they obtain lucibufagins to defend themselves and their eggs. Lacewing larvae Chrysopa slossonae cloak themselves in trash, making themselves resemble woolly aphids and fooling the ants that herd them. Beetles of the genus Elytroleptus both mimic poisonous lycid beetles and prey on them; if they sometimes become unpalatable themselves, they would combine Batesian and Müllerian mimicry.
Ozaenine beetles direct jets of fluid against attackers using the Coanda effect. Daddy-long-legs Vonones sayi accurately administer benzoquinones onto attackers using their forelegs. Dienutes beetles emit gyrindal to make themselves unpalatable when swallowed by fish, using slow release to combat "oral flushing". Nasutitermes exitiosus termites spray gum against ants. And the secretions of Glomeris millipedes sedate attacking wolf spiders.
Detachable scales help moths escape from orb spider webs. Orb spiders take their webs down during the day, or mark them with "stabilimenta" so birds can avoid them. Argiope spiders deal better than Nephila ones with bombardier beetles and stink bugs, wrapping them in silk before biting them. If not killed, bugs use saliva to weaken the glue and harden the silk, making it easier to break free.
Insect defences have naturally inspired a variety of "circumventers", or predators with ways of getting around chemical defences. Grasshopper mice jam the "armed" tails of Eleodes beetles into the sand before eating them from the head down, stopping just short of the poison glands. Phengodid beetles inject a rapid-acting poison into the necks of millipedes, crawl away and bury themselves in the sand for an hour or so, then return to eat the innards, leaving the poison sacs. Insects of several kinds consume leaves of latex-producing plants after first puncturing key veins to isolate them.
Synchlora caterpillars decorate themselves with flower petals as camouflage. The plant Mentzelia pumila uses lethal defensive spines against insects, but the aphid Macrosyphum metzeliae, moving carefully on long legs, not only feeds on the plant but is protected by its spines.
Insects such as grasshoppers and sawfly larvae use toxic chemicals from the plants they eat: waxes, slime, pine resin, eucalyptus oil, turpentine. Cochineals produce carminic acid not as a dye for humans but to deter predators, but some of those not only cope with it but turn it to their own ends:
"Laetilia, Hyperaspis, and Leucopis illustrate nicely now opportunistic strategies can differ from insect to insect. Evolutionarily all three have achieved the same thing. Through specialization they have 'crashed' through the defensive chemical barrier of their host, and have seized the opportunity of appropriating the host's weaponry for protective purposes of their own. All three use carminic acid for defense, but each does so in its own way. One expels the compound orally, another does so from the rear, and the third deploys it by bleeding."
Cantharidin is poisonous, but has been used as a primitive "Viagra". It is used for protection in meloids (blister beetles) through defensive bleeding. In Neopyrochroa beetles, cantharidin is transferred by males to females, and hence to eggs.
Utetheisa moths use alkaloids derived from plants for defence: males transfer alkaloid to the females, after using a derivative to attract them, and the females use it to protect their eggs.
And these are just some of the insects Eisner covers.
The science in For Love of Insects comes from many disciplines. There is chemistry, describing the structure and synthesis of defensive chemicals and explaining how they were collected and isolated. There is anatomy, looking at defensive structures and organs for producing, storing and targeting defensive compounds. There is ecology, looking at when and against which predators insect defences work, at the role of mimicry, and so forth. There is ethology, looking at behaviours for getting around defences, at transfers of chemicals in mating, and at different life stage strategies. There is evolutionary theory, looking at how all these features evolved, at predator-prey coevolution, sexual selection, and so forth. There is history and anthropology, looking at the role insects have played in human life. And more.
Eisner also includes some details of experimental methodology and design, and background on the mechanics of science; he generously acknowledges his collaborators over the years.
For Love of Insects is illustrated with extraordinary photographs. These are not necessarily the kind to excite an art macrophotographer, but they include action photos of insects, attacking and being attacked, that are both dramatic and informative. Eisner includes some discussion about how the high-speed photography involved was done. There are also electron micrographs and diagrams illustrating anatomical details.
For Love of Insects is the grand synthesis of a veteran scientist looking back, sharing his knowledge and experience but above all his excitement and wonder at the marvels of the natural world. Anyone curious about insects, or indeed natural history, should find it a joy to read.
December 2006
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