A cockroach and jewel wasp are locked in battle— but not for long. The wasp latches onto the cockroach, arcs her body, and inserts her stinger precisely into a cluster of nerves in the cockroach’s thorax. The venom that surges out temporarily paralyzes the cockroach’s front legs. She then stings its brain, where her venom blocks its fight-or-flight response. From here on out, the cockroach is essentially a zombie. The wasp snaps the cockroach’s antennae in half, uses the broken pieces as straws to feed off its blood-like hemolymph, then leads it into a subterranean lair. She lays an egg on her victim and carefully seals the burrow, which becomes her offspring’s nursery— and the cockroach’s crypt.
Over the following weeks, her larva hatches, bores into the cockroach, eats it alive, pupates in its carcass, and emerges as an iridescent adult. This gruesome tale is just one example of parasitoidism, an evolutionary strategy employed by most wasps. Parasitoids feed off other animals as they develop, usually killing their hosts in the process. In fact, these insects are about to meet their ends by way of wasps— each in a uniquely dreadful manner. This wasp targets the ladybug, planting an egg inside its body. When the larva hatches, it consumes the beetle’s body fat. It eventually emerges, but the ladybug’s duty isn’t done. It’s now semi-paralyzed, possibly due to a viral infection the wasp gave it. The larva spins a cocoon between its legs, and the still-alive-but-bewitched beetle stands guard. When a predatory lacewing larva approaches, the ladybug twitches, scaring it off. Many other creatures avoid the ladybug altogether because of its bright coloration, which advertises its toxicity.
After a week, an adult wasp appears, leaving its hapless helper’s corpse behind. Next is the tiny but fierce crypt-keeper wasp, which targets gall wasp larvae like this one. The gall wasp larva is also parasitic, but in a more vegetarian sense. It’s feasting on this oak tree, tucked away in a chamber on one of its branches. Soon, it has company. The crypt-keeper wasp adds her egg into the mix. The gall wasp develops, and eventually begins chewing its way out, as it normally would. But it makes a smaller-than-usual hole and gets stuck. The crypt-keeper larva eats through the gall wasp’s corpse, pupates within it, then makes its debut, crawling out of the dead wasp’s head. The final victim is this caterpillar. It would have become an owlet moth that fluttered in the cool night air, but a few weeks ago, while developing in its egg, this wasp injected an egg of her own. The caterpillar hatched and began growing. And in a process called polyembryony, the wasp spawn divides repeatedly inside of it. But a second kind of wasp also lays her eggs on the caterpillar. The original brood senses this and further develops into two distinct castes. What was one egg becomes thousands of larvae: some of them are reproductives, others are soldiers.
The caterpillar is now both wasp buffet and battleground. As the reproductive larvae consume its insides, the soldiers kill the other parasitoids. The reproductive larvae morph into adults and the soldiers die within the host. Needless to say, the result for the caterpillar is … very bad. This was just a peek into the prolific province of parasitoid wasps. Some venture underwater to find their hosts. Others are hyperparasitoids, whose victims are other parasitoid wasps. Scientists are still pulling back the curtain on these creatures. They can be hard to collect and quite small: the world’s tiniest known insect is a microscopic wasp that parasitizes barklice eggs. Though much remains unknown, some researchers suspect that parasitoid wasps are among the most diverse animal groups— perhaps the most diverse. Wasps have been perfecting their brand of parasitism for some 247 million years, all to give their offspring the very best opportunities life has to offer.
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