This striking red wasp with iridescent blue wings has been fairly visible on Queen Anne’s lace lately. It’s a Western Red Spider Wasp in the Tachypompilus genus. Do spider wasps eat spiders? Yes, but maybe not in the way you’d assume. While you might see a female packing off with a spider, it’s the larvae, not the adults, that eat them. Adults, like most adult wasps, are vegetarians.
Female spider wasps use their front legs to dig a hole in loose dirt or rotted wood. Then they sting a spider to paralyze it, drag it to the hole, lay a single egg in the spider, and cover it up. For an insect, this spider hunting seems like a lot of work for one egg, so it must be fairly foolproof. I haven’t yet found how many times a female will go through this process, and it may be that no one knows.
The subsequent wasp larva spends the next few months using the spider as its live-in pantry. Note: The spider is still alive. The larvae leave the vital organs intact to preserve the food as long as possible.
The curled antennae indicate the wasp pictured here is female. Western red spider wasps typically use wolf spiders as their provisions. It’s well documented that bigger spiders lead to bigger wasps. It follows that larger spider-stores produce more female wasps. Male spider wasps are smaller because they don’t need to heft spiders or dig holes. One article (below) says that some spider wasps determine the sex of the young by choosing which eggs to fertilize and make female. Thus, the big spiders get a fertilized egg.
A University of Florida article (below) has fascinating details about the female Rusty Spider Wasp. Also in the Tachypompilus genus, this wasp does some impressive gymnastics to set up its nursery. She gets into a pre-dug hole next to an immobilized spider, flips it on top of herself, so she’s under the spider on her back, and then oviposits the egg into the spider! I wonder if the Western Red also performs the egg-laying flip?
The largest spider wasps, by the way, are called Tarantula Hawks and their chosen food is exactly what it sounds like. These Pepsis genus wasps are large, but still much smaller than a tarantula, and the coloring is the exact opposite of the Western Red: a shimmery blue body with reddish wings.
University of Florida on the Rusty Spider Wasp: https://entnemdept.ufl.edu/creatures/MISC/WASPS/rustyspiderwasp.html. Accessed 7/20/21.
BBC story on female wasps choosing sex of offspring: http://www.bbc.com/earth/story/20150109-the-wasp-that-scares-tarantulas. Accessed 7/20/21.