Sharp, accurate, deadly

I never confessed to anybody, especially co-eds, that the assignment scared me spitless. I was working on a farm during a college exchange program in Texas when I was given the job of clearing out an old, disused milking shed - all on my own. I had to set aside any salvageable old equipment, haul out and burn broken timbers and shovel up that stuff (know what I mean?). No, I wasn't afraid that a serpent might slither in unannounced. It was the mud daubers that bothered me. I reckon every species found in east Texas was nesting there that summer. The inside walls were plastered with mud nests of every conceivable form, some old, but way too many for my liking in process of being built and provisioned. I ducked and bobbed constantly as wasps by the score weaved and droned past; I need not have feared - I never "got bit". I wish I could have another crack at it; today, wasps are my favorite insect.

The need for brevity precludes listing their many virtues. Here we ponder the embarrassment wasps (like everything else in nature) cause evolution's cause. Most wasps and their larvae are flesh eaters; eggs of such species are always laid on or in a living "bug". Some species, for instance, inject their eggs into a caterpillar where they hatch and develop by eating their host from the inside out. As fans of Walt Disney's "The Living Desert" remember, others do battle with giant spiders which they sting into paralysis. When the venom has done its job, the wasp drags the spider into a prepared nest cavity and lays an egg on it; the hatchling grub has fresh flesh to dine on. Mud daubers, too, stock their mud nests with paralyzed living bugs as food for their grubs. Herein lies one of creation's many natural wonders. First, in many cases wasps must sting their prey in precisely the right spot or failure will result. Second, the venom of wasps is a wonder of biochemical wizardry, each species mixing up its trademark brew of poisons targeting precise elements within the victim's body and geared to performing very specific tasks. For wasps to succeed, both features must be fully developed and functioning perfectly - "almost right" is just not good enough. Robotic engineers have spent years developing both the electronic circuitry and the "anatomy" of robots to get them to the point they work. Robots can do nothing compared with wasps.

Even those species of wasp whose venom works by diffusing throughout the body and blocking the transmission of nerve impulses into the muscles (thus paralyzing the victim) can't just jab their ovipositor any old where for, even if they succeed in puncturing the tough "skin", the location may not be conducive to the spread of the toxin. When the Australian digger wasp spots a bush cricket while out scouting, she, "dives, knocks it over and stings it, apparently several times, on the ventral side of the thorax and abdomen thus paralyzing it permanently"¹. The placement may be far more precise and discriminating than this older report suggests. More recent studies of a European species of digger wasp show that, "The wasps paralyze the prey by injecting

their venom directly into each of the three thoracic ganglia and the suboesophageal ganglion"². Now that's precision inexplicable by evolution theory.

The sting must be directed to a soft joint between hard plates to succeed in gaining entry; to accomplish such directed behavior requires the services of a highly-sophisticated piece of nerve circuitry. How can random mutation and natural selection possibly ensure the simultaneous acquisition by the wasp of a perfectly-designed stinger, the right mix of complex venom molecules and such complex seek and attack behavior? They can't, and that's all there is to it.

Wasp venom is most definitely not an example of "one size fits all". We can barely begin to catalog all the venom cocktails used and their mode of operation. Whereas some venoms induce paralysis by blocking general nerve impulse transmission between nerves and muscles, others act quite differently. One wasp that lays its eggs on the outside of a living caterpillar also injects a "variety of maternal products"³, including venoms, into the host that affect it in a number of different ways but, in this case, not including paralysis. Experiments show that the venom prevents molting, a vital "adaptation" for externally placed eggs that would be cast off with the molted skin. Another that places its eggs inside the victim injects a venom that somehow blocks the host's immune system from encapsulating the eggs and preventing them from hatching⁴.

Researchers in recent years have studied one species that would seem to win the prize for sophistication. Ampulex compressa is its name, and cockroach mastery is its game. On finding a roach it deftly swings its stinger under the unwitting insect and instantly thrusts it into a ganglion of nerves in the thorax. Almost immediately the venom paralyses the front legs, making the roach "fall on its knees". Paralysis only lasts a few minutes, but it's long enough for Ampulex to then go for the neck and head where a most remarkable thing occurs. In one insertion, the wasp's sting goes to two different, extremely precise locations in the roach's "brain", in each of which it leaves a tiny drop of venom - the insect equivalent of Robin Hood's archery accuracy here. As one researcher reports, "To achieve such a precise stereotaxic injection, the wasp's sting must bear sense organs to identify its neuronal targets"⁵. The result is spectacular. The roach is perfectly capable of movement, but is no longer in control of it. Sudden movements that would make it flee for its life before now have no effect. The roach has become, in effect, a zombie. When the wasp grabs one of its antennae and starts to lead it to its den of doom, the cockroach, "follows the wasp in a docile manner like a dog on a leash" (Libersat). You don't have to be mad to contend that such sophistication is a natural outplay of a primordial explosion, but it would help.

¹Ribi & Ribi 1979, Natural history of the Australian digger wasp Sphex cognatus Smith, Journal of Natural History, 13 : 693-701

²Ferber et al 1996, Digger wasp vs. cricket: application of the paralytic venom by the predator and changes in behavioural reactions of the prey after being stung, Naturwissenschaften, 83: 467-470  

³Weaver et al 1997, Role of Ectoparasitoid Venom in the Regulation of Haemolymph Ecdysteroid Titres in a Host Noctuid Moth, Archives of Insect Biochemistry and Physiology, 35:169-178

⁴Parkinson & Weaver 1999, Noxious Components of Venom from the Pupa-Specific Parasitoid Pimpla hypochondriaca, Journal of Invertebrate Pathology, 73: 74-83

⁵Libersat 2003, Wasp uses venom cocktail to manipulate the behaviour of its cockroach prey, Journal of Comparative Physiology A, 189: 497-508