(photo by Jen Ochoa, Outreach Coordinator, San Diego Canyonlands)
Mother Nature
by Chance Austin-Brecher, Restoration Supervisor, San Diego Canyonlands
Motherhood is hard work. It’s dirty, it’s exhausting, it’s often thankless, and sometimes it requires hunting, paralyzing, and dragging giant spiders long distances for your larvae to feed on.
Tarantula hawk wasps are an infamous member of the family Pompilidae, consisting of over 5,000 species of wasps that mostly prey on spiders as a food source for their young. The process is quite grisly, but also a very interesting one that’s calculated to ensure the survival of the species. As it happens, some members of the order of insects to which the tarantula hawk wasp belongs, Hymenoptera, have the incredible ability to choose the sex of their offspring. When a female wasp locates a tarantula, it will sting the spider in a spot that paralyzes the victim within seconds. The wasp will then drag the spider back home to the burrow it’s built, where it lays a single egg on top of the still living spider. Once the egg hatches, the larva’s first instar will feed on the immobilized tarantula’s blood. As it grows, the offspring will gradually eat everything but the heart and nervous system, until, finally, the last instar of the larva finishes its meal, putting the spider out of its misery. All in all, the spider will have spent the last month of its life slowly being eaten. The larva, satiated, next spins its cocoon to pupate, emerging weeks later as a full grown adult.
The sex of the new wasp, as mentioned earlier, will be entirely determined by the mother. Simply put, a fertilized egg becomes female, an unfertilized egg becomes male. Because female wasps have to do all of the hard work of building a burrow, hunting for prey, killing it, and dragging it all the way back, mothers will reserve the biggest spiders for female larva to feed on. Male tarantulas, who don’t have as much meat (they spend most of their time searching for a mate), are typically reserved for male wasp larvae, because, as it happens, male wasps really only spend their time trying to attract mates as well. It all really boils down to the fact that bigger spiders means bigger wasps and the females have to be the bigger wasps because they have to do all the insane and difficult things that motherhood demands. After all, what mother wouldn’t kill a spider eight times their weight to feed their children?
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