A quick update on a post I did two years ago on a Tale of Two Spiders.

Parasitic wasp larva on orbweaver spider (click photos to enlarge)

A friend had spotted an odd-looking spider that had spun a web on her car. Closer inspection revealed the spider had a hitch-hiker, a parasitic wasp larva. I watched the spider over the next few days until one morning, it was no longer in a web, but was lying on the ground, shriveled and dead.

Wasp larva spinning cocoon, suspended in a special web made by its spider victim

Completed cocoon

The wasp larva was now much larger and was constructing a cocoon in a small sturdy web that had been made by the spider before its demise. I found references online where scientists speculated that the parasite somehow managed to coerce the spider into making an alternate style web before it was totally drained by the feeding larva.

Studies reveal the wasp larva hijacks the behavior of the spider

A recent study published in the Journal of Experimental Biology (and reported in the New York Times a little over a week ago) now reveals that these wasp larvae (or at least similar species to the ones I photographed) incapacitate their hapless victims by taking control of their nervous systems and turning them into zombies. How cool is that? The spider’s final act is to construct a small, tough web that helps support and protect the cocoon spun by the wasp larva as it readies itself to pupate. The researchers found that this last web made by the hapless spider was similar to one they make as a resting or molting site web. In other words, this design is something already in their web-building repertoire, but the wasp larva hijacks that genetically programmed behavior for its own purpose before killing the spider. They also found this last cocoon web was a beefed-up version of the resting web usually made by the spider, which means it probably offers even more protection for the master wasp larva. The scientists suspect the spider’s behavior is triggered by a substance similar to the spider’s molting hormone injected into the spider by the larva. Zombies…fact or fiction? You be the judge.