Newly Described Parasitic Wasp Likely Saws Itself Free From Its Host

No one has ever observed this new species of wasp in the wild. Carolyn Trietsch

After sitting in a drawer for decades unnoticed, scientists have described a new species of parasitic wasp, but one that has a unique and pretty brutal lifestyle.

You can probably forgive museum staff for overlooking the tiny insect, which was collected in Costa Rica in 1985. Around the size of a sesame seed, Dendrocerus scutellaris, described in the Biodiversity Data Journal, doesn't look like much to the naked eye. But look a little closer, and you’ll see a beautiful pair of branched antennae probably used for seeking out the opposite sex – or possibly even hosts.


Very little is understood about the new species as it is only known from a few specimens collected over 30 years ago, so the researchers have had to turn detective.

They knew that the little wasp was probably a parasitoid, in which the larvae of the insects feed on hosts as they grow and develop. Wasp parasitoids come in one of two flavors. There are the ectoparasitoids, where the adult female wasp lays her eggs on the surface of the host, allowing newly hatched grubs to chow down on the unfortunate insect.

But there are also the slightly more disturbing endoparasitoids. These are wasps that manage to lay their eggs directly inside their hosts, so that when their darling larvae hatch they have a veritable feast of fresh organs and flesh. The developing larvae basically eat their host from the inside out, before bursting free as seen in your favorite 70’s sci-fi horror.

Now no one has actually observed D. scutellaris in the wild, but features on its body suggest how it might behave and reproduce. When endoparasitoid wasp larvae are done emptying the body cavity of their host, they will often sit inside the husk of the insect to mature. But in order to perform their final reveal, they need a way to get out, such as large mandibles to chew themselves free.


Noticeably, this latest species lacks any large gnashers. Instead, it has a unique saw-like row of spikes running along its back. The researchers suspect that these might be the key to the unusual wasp's lifestyle, and that after growing inside their host, the newly formed wasps rub their backs against the inside of the empty shell and effectively saw their way to freedom.

“While their lives may sound gruesome, parasitoid wasps are harmless to humans and can even be helpful,” the researchers explained. “Depending on the host they parasitize, parasitoids can benefit agriculture by controlling pest insects like aphids that damage crops.”

Who the host is, or even if the researchers' assumptions are right, still remains to be seen, but they hope that by giving the little creatures a name they will soon find out. 


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