"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

September 10, 2019

Zatypota maculata

Many people are afraid of spiders and while spiders are generally harmless to people for the most part, their appearance are just too nightmarish for many. But spiders have their own very real nightmares to contend with - spider wasps. While adult spider wasps have a comparatively placid diet composed of mostly nectar, their parasitic larvae need fresh food - in the form of fresh, living, spider meat.

The modus operandi of these wasps is to lay their eggs on a living spider, and the developing wasp larvae then devour the spider alive. In some cases, the wasp larva even makes the spider spin a cocoon for them before killing them. Zatypota maculata is a species of spider wasp from Japan that has some specialised tactics when it comes hunting spiders - that is because the spider it is hunting is itself rather special.

Zatypota maculata laying an egg on a paralysed spider (photo from: Figure 3 of the paper)

The spider in that wasp's cross-hair is Nihonhimea japonica, and it belongs to a family of spiders call Theridiidae which includes the black widow spider. They are known for weaving tangle webs that trap prey in a wide range of different ways. In the case of N. japonica, it constructs an elaborately structured, three dimensional web, the centre of which sits a piece of dead leaf that serves as the spider's hideout. At the bottom of this 3D cobweb is a flat silk sheet that looks like a miniature safety net. But in this case, instead of a life-saving measure, the net is a deathtrap. When an insect stumbles through the 3D cobweb, they get knocked down to that flat bottom net (called, appropriately enough, a "knockdown 3D web"), this alerts the spider which will then drop down to claim its prey. Here is a video of it in action.

Zatypota maculata takes advantage of that hunting tactic to turn the hunter into the hunted. Since the spider sits in a hideout located in the centre of an elaborate cobweb, it is not easy to get to it. There are a few ways that Z. maculata go about this; she can either carefully climb up the spider's web and make her way to the centre where the unsuspecting spider is located, or if she's not feeling as patient, she'll throw herself into the knockdown web, and when the spider comes down to collect its catch of the day, the wasp turns the table on it.

Depending on the spider's response to her intrusion, Z. maculata will adjust her approach accordingly. Sometimes, for whatever reason the spider just won't respond to the wasp's presence on the knockdown web - so that is when she will have to go climbing after it. Once within reach, Z. maculata pounces on the spider, paralyses it, and lays her eggs on it to turn its body into a living larder for her babies. But sometimes the spider has already been visited by another Z. maculata. In that case, she would use her stinger to scrape off or even kill the eggs or larvae that are already on the spider - the wasp baby is going to need a lot of food to fuel its growth, and anything less than a whole spider will just not do.

There are many other species of spider wasps out there that specialise on different theridiid spiders. Since each of those spider has a different web architecture, this means the spider wasps that target them have also evolved many different tactics. Some pretend to get trapped in the web to entice the spider out, others patiently stakeout near the web and wait for the spider to come out to launch an ambush, and there are others still that boldly plunge straight into the heart of the web and sit there to wait for the spider to come back eventually after being scared off by the sudden intrusion.

Given the wide range of extraordinary behaviours found among different spider wasps for attacking spiders, there might even be other wasp species out there armed with special tactics that we have yet to discover.

Takasuka, K., Matsumoto, R., & Maeto, K. (2019). Oviposition behaviour by a spider‐ectoparasitoid, Zatypota maculata, exploits the specialized prey capture technique of its spider host. Journal of Zoology 308: 221-230.