Wasps are commonly known as being scary arthropods with a strong sting that is extremely painful to humans. However, this is only the tip of the iceberg, because wasps are incredibly vicious predators, that have survival strategies that are far more gruesome than any gore film out there.
There are certain wasp species from the order Hymenoptera that are particularly sadistic parasites. These species are called parasitoids, which means that they kill their host once it serves no use to them anymore. Parasitoid wasps usually sting their hosts and insert their eggs inside them. These eggs develop into larvae, that essentially grow inside the host and then break free when they are fully grown, thus killing the host.
A recent study conducted by a team of researchers at Kobe University in Japan led by Keizo Takasuka focused on a particular wasp species called Reclinervellus nielseni, that hijack spiders and use them for growing out their larvae. The researchers collected Cyclosa argenteoalba spiders for their study, so that they could get a closer look at the methods employed by the vicious parasitoid.
As opposed to other Hymenopterans, the R. nielseni wasp does not sting the spider to insert its eggs inside it. The female wasp simply lays its eggs on the surface of the spider’s body, that hatch into larvae that remain attached to the spider and simply use it a food source, in the initial phase. The larvae feed on the spider’s haemolymph and they start growing and growing.
What is particularly odd about this species is that the larvae also release a substance as they feed, that the researchers hypothesize could be similar to a hormone. This substance seems to have a very strong effect on the spider, as its instinct to build webs becomes exacerbated.
And so, the parasitized spider beings to build a very strong web, that can be as much as 40 times thicker and stronger than its usual web, to accommodate the wasp larvae. The web that it builds is a special type that spiders themselves use when they molt. Molting is the process that spiders go through during their growth period, when they shed the outer layer of their cuticle so that they can grow bigger and stronger.
This special type of web is not sticky, so that the spider is safe during its molting phase. The wasp gets a bigger and better version of this, and it waits patiently for the spider to build it. When the spider has finished the web though, the wasp becomes extremely aggressive and starts sucking out all the haemolymph and other nutrients from it, until the spider is killed.
The larvae literally sucks him dry and then it uses the web that the spider built to stay safe and grow into its next evolutionary stage. The spider most likely supplies enough nutrients for the larvae to develop into its next stages and eventually become an adult wasp of its very own.
The Kobe University study was recently published in the Journal of Experimental Biology and it describes the patterns displayed by the parasitoid wasp in great detail. Reclinervellus nielseni is one of the most aggressive parasitoids known up to this point and it will most likely be the subject of future research that will focus on the effects that the substance released by the larvae has on its spider host.
Image Source: smithsonianmag