The Predator Plundered

The Predator Plundered

Frank Graham Jr.
Published: 04/29/2009

This early spring afternoon, as I walked past a still-fallow corner of our vegetable garden, I noticed a metallic dark-blue insect darting frenetically through the tufts of grass and weeds already growing there. It was a slender little spider wasp, maybe a half-inch long, its smoky wings ceaselessly twitching and fluttering as it ran about searching, searching, for something. Ah, found it! The wasp suddenly reappeared from behind a clump of weeds and dragged into view an adult female wolf spider.

I had come in partway through one of nature’s fascinating encounters in miniature. Arguably spiders, in their omnipresence and teeming numbers, are earth’s dominant terrestrial predators. Yet even in the apparent placid environs of a vegetable garden their most efficient enemies, female spider wasps (family Pompilidae), relentlessly hunt them.

I had missed the violent bit. Once a wasp has spotted a spider in the open, the issue isn’t in doubt. The tough little insect dashes in, stings her victim with a powerful venom that paralyzes, but doesn’t kill: because in this case, the victim isn’t destined to be a meal for the killer but for a creature that doesn’t yet exist—the wasp’s offspring.

And so, as I watched, the wasp grasped the limp spider’s hind legs in her jaws and, walking backward with wings still vibrating, began pulling her burden (as large as herself) across the garden’s surface. Once or twice she stopped and momentarily abandoned the spider. Half running, half flying, the wasp scouted the surrounding area for a suitable place for her victim’s entombment. Then she rushed back, spent another minute or two searching frantically (I know it’s here someplace), happened upon the comatose spider, and continued the laborious chore of dragging it over and around stones, grass tufts, and other small obstacles.

At last the wasp made her decision. She hoisted the spider atop an abandoned board, like a kayoed boxer being lifted onto his stool, then scurried to the selected point near a grass clump and began digging furiously into the soil. Within five minutes she was out of sight, down a vertical hole, in diameter the size of a lead pencil. The only sign of progress was a slowly expanding mound of soil around the hole. Once the wasp darted out of the hole to make sure the spider was still on the board (there are other insects who might steal her prey). But she quickly returned to the chore of digging her nest with strong, spiny front legs.

The wasp dug for 30 minutes. Then she bolted to the nearby board, grasped the spider and, backing into the hole, pulled it tail-first after her. I had a last glimpse of the blunt, eight-eyed head as it vanished. At the bottom of the shaft the wasp will lay a single egg on her prey’s abdomen. When the larva hatches in a few days, it will find the grisly legacy of fresh meat left by its mom—a paralyzed creature it will eat alive.