The bold and belligerent wasp is never welcome. Still one might hesitate before terminating its threatening presence on a summer’s day to reflect on how its life and habits exemplify to the highest degree the intelligence and purposiveness (or so it seems) of even the simplest animals. 

For this we are indebted to the reclusive self taught scientific genius Jean Henri Fabre whose patient observations in his desolate garden in the South of France revealed more new facts about the hidden world of insects than anyone before or since.

Fabre loved insects in all their glorious diversity but his greatest passion was the solitary “hunting” wasp. Two examples must suffice, but first a brief, necessary digression on that most distinctive feature of the wasp’s anatomy, its narrow thread-like waist (or petiole). Its “purpose” is in conferring great mobility to the abdomen — up and down, from side to side- allowing the wasp to position the stinger at its tip with devastating accuracy at the most vulnerable part of his prey. 

Once dispatched, the wasp squeezes all the honey out of the bee’s stomach

But that narrow waist so constricts its gut it can only feed on liquid nectar. Its hunting skills are thus reserved for the benefit of its carnivorous offspring in their larval phase, to whom it delivers (depending on the species) a regular supply of fresh live caterpillars, bees, spiders or other insects immobilised by its paralytic venom.

We start with the philanthus wasp, “the lover of flowers”, not just for their delicious nectar but also the haunt of its chosen victim  — shocking to relate  — the munificent honey bee. First she builds her nest in a sandy bank, digging furiously with her front legs, the sand flying out behind her. She lays her eggs in its carefully constructed cells, emerges and rakes over the opening. Before flying off she circles over her burrow in ever widening loops taking her bearings of the immediate vicinity to ensure she finds (unfailingly) the concealed entrance on her return.

 “The pursuit of knowledge is not without its cruelties” wrote Fabre. Placing a philanthus wasp together with a honey bee in a glass jar he observes its mode of attack. “Turn by turn, tumbled and tumbling, they roll over and over”. The philanthus pinions her victim to the ground and curves her abdomen forward to deliver her paralysing sting “with the certainty of a skilled surgeon” into the vital cephalic ganglion of nerves just beneath its neck. 

The bee goes limp but the drama is not quite over. The assassin remains firmly clasping her prey for a couple of minutes less she be harmed by any residual reflex movement of its formidable stinging apparatus. She then squeezes all the honey out of the bee’s stomach — a necessary precaution Fabre subsequently established against it becoming contaminated with a fungal infection that might harm the philanthus larvae when munching through its entrails. 

The hunting wasp must sting each set of caterpillar legs in turn

Next the ammophila (sand loving) hunting wasp whose instinctive knowledge of the neural anatomy of its caterpillar prey is yet more impressive. Having built her nest and laid her eggs she must locate the caterpillar of the noctua moth family to provision the larder  — a formidable task as it lives underground feeding on the stems of young plants. 

How she detects its presence no-one can tell but, once unearthed, ammophila bestrides her victim several times larger than herself. Seizing the back of its neck with her curved mandibles she injects her paralysing venom just beneath its head. This is the essential strike, but the caterpillar (unlike the bee) is segmented each of its seven pairs of legs controlled by a separate nervous circuit. The ammophila proceeds to move methodically down its back stinging each set of legs in turn. “The surgeon has finished. The patient lies on the ground motionless, incapable of resistance” before being unceremoniously dragged back through the undergrowth to become a tasty meal for the hungry larvae back in the nest. The further thirty thousand species of hunter wasps provide numerous ingenious variations on the same theme. 

Fabre stoutly maintained these highly specialised purposive patterns of behaviour could not readily be accommodated by theory of gradualist evolutionary transformation. “The development of instinct by degrees is not possible” he wrote. “The wasp must excel from the outset in preparing the provisions for its larvae or leave the thing alone”. It is certainly difficult to conceive how that wasp-sized brain  — no bigger than a couple of grains of sand-could give rise to so complex and protean forms of activity.