Wasps can be a rather … mean-spirited bunch, particularly when it comes to raising their offspring. Not that they’re mean to their offspring, but they enlist all kinds of bizarre parasitizations of other insects to help raise their young. There’s one variety, for instance, that injects up to 80 eggs into living caterpillars. The resulting larvae devour the caterpillar’s insides, yet leave it alive, then erupt out of its body and mind-control the poor thing to protect them as they spin their cocoons.

New research out today in the Journal of Experimental Biology details the intricate life cycle of another parasitoid (that is, a parasite that kills its host) wasp, Reclinervellus nielseni, which somehow mind-controls spiders into building a special web to protect it. That’s before the wasp kills the spider by sucking out its insides, of course.

Now, the host spider, Cyclosa argenteoalba, spins different kinds of webs for different purposes. It has the classic orb design it uses to catch prey, but also a minimalistic and unsticky “resting” web it spins before molting as it grows (creatures with a tough exoskeleton, such as crabs and insects and spiders, have to periodically shed their shell as they grow). Obviously catching insects isn’t in its best interest when it’s hardening up a new exoskeleton, so it wants to avoid catching anything.

So, the wasp. Instead of injecting the spider with an egg, like the caterpillar wasps do, she simply lays it on the host. The egg hatches into a larva, which feeds on the host’s hemolymph—the arthropod version of blood—and begins mind-controlling the spider to build a web similar to the resting variety.

The mechanisms here, as is largely the case with other mind-controllers in the insect world (there are a lot), are still a mystery, though certainly it comes down to some kind of chemical. It may be that the larva is injecting the host with a chemical similar to the hormone that kicks off the spider’s molting, encouraging it to build a resting web. That would mean, though, that the parasite would somehow have to keep the spider from actually molting.

Thus the wasp seems to have figured out how to exploit a web plan that the spider has been using for millennia. As an added bonus, that silk actually reflects a whole lot of ultraviolet light, making the larva, now spun into a cocoon, that much brighter and therefore more conspicuous to passing birds, which can see UV. That might seem counterintuitive to the whole survival thing, but think of it as a traffic cone that helps birds steer clear of the web instead of running into the structure and destroying the pupa. A really, really disturbing traffic cone.