Euplectrus – Caterpillar Ectoparasitoid

So far the Genus Euplectrus has only been found in moth caterpillars. There are dozens of species in the Euplectrus Genus.

Walking at the side of the road, I saw a caterpillar with a bumpy lump attached to it.

I picked it up and took photos. It was fast, scurrying across my hand. I’d touch its head and it would tuck it under for an instant before taking off the opposite direction. Whatever the bumpy lump was, I could tell that it wasn’t hindering its movement. I placed it in a paper bag and returned home.

I placed the bag in my office, where I raised caterpillars that I found as I walked. The next morning I opened the bag to place the caterpillar in a small cup to raise it. It clearly was dead. The bumpy lump had become a row of little piglets, reminding me of a sow nursing her pigs. They were lined up underneath the caterpillar, draining the fluid from it.

I watched off and on during the day as the caterpillar slowly became thinner. The next morning, all that remained of the caterpillar was dry skin. When I lifted the skin, a row of tiny cocoons were lined up underneath it. Several days later, small wasps emerged from the cocoons.

After a good bit of internet research, I was able to loosely identify them as an ectoparasitoid. I knew about parasitoids, but the term ‘ectoparasitoid’ was new to me. “Ectoparasitoids develop outside the host body. These parasitoids are frequently attached or embedded in the host’s tissues.”

Since that time, I’ve found many moth caterpillars with this ectoparasitoid attached to them.

Before the female wasp lays eggs, she injects a venom that keeps the caterpillar from molting again. This is necessary as they are attached to the cuticle/skin. Molting would shed the parasitoids along with the cuticle.

Some species will paralyze the caterpillar before laying eggs while other species will not paralyze them. Some species lay only one egg while others lay up to hundreds of eggs on one caterpillar.

Eggs are attached to the caterpillar. Larvae hatch and stay at the same spot as they hatched, drinking hemolymph/blood of the caterpillar while the caterpillar remains alive. They continue to grow, staying in the same spot.

Egg laying to adult is usually about two weeks.

Unlike caterpillars that produce silk from spinnerets under their heads, Euplectrus secrete modified malphigian tubules through the anus to create their loose cocoons.

Some species make cocoons only underneath the caterpillar. Other species make cocoons all around the caterpillar, somewhat enclosing it in cocoons.

As of March 2015, fewer than 200 species had been discovered in the world. Eight species were known in North America.