Mantidflies drink spider blood, eat spider eggs

By Jeff Mitton

I was hiking in the canyon of the Purgatoire River when something odd buzzed my head and landed in a nearby juniper.

It looked like a wasp, but it did not fly like a wasp and its front legs were enormous and folded. The wind kept the branch swinging back and forth so I was unable to get a decent photograph.

Two years later, University of Colorado entomologist Cesar Nufio asked me if I would like to photograph a mantidfly that he had just caught near Sugarloaf. His recent trophy was the same species as the strange insect I had seen in the Purgatoire Canyon. I chilled it in a refrigerator to prevent it from flying while I photographed it.

The mantidfly, Climaciella brunnea, is widespread in North America, and although it forms aggregations in some parts of its range it seems to be rare here.

Superficially, it looks like a wasp, but its front legs are raptorial, or modified for hunting and are certainly not those of a wasp. One segment of the front leg is thick and armed with barbs. The outer segment of the leg can extend, snare an insect and then hold it against the prominent barbs so that it cannot escape.

The pronotum, or first segment of the thorax, is strikingly elongated, making the mantidfly appear to have a long neck. It has four membranous wings, but it is a clumsy, noisy flier.

The mantidfly has the raptorial front legs of a praying mantis and otherwise it looks like a wasp, but it is not closely related to either a praying mantids or wasps. Its closest relatives are the delicate, attractive green lacewings.

C. brunnea is distinctive among the three other species of mantidflies native to Colorado in that it is a mimic of the western paper wasp, also known as the yellow-legged paper wasp, Mischocyttarus flavitarsis.

While the noisy flight and raptorial legs are dead giveaways, the rest of the body and coloration are quite convincing copies of the wasp. Presumably, a close resemblance to a paper wasp would make most predators look for less formidable prey; who wants to tangle with a nasty wasp?

A female mantidfly lays a few hundred to perhaps a thousand eggs, rests for a few days and then repeats the effort several more times. Eggs are laid on stalks on the underside of leaves.

Nothing remarkable here, but everything that follows is remarkable.

The larvae hatch out, attach caudal suckers to the substrate and then rear up, waiting for a spider to shuffle by. They latch onto a wolf spider and climb aboard.

But if they have inadvertently climbed aboard a male spider, they must wait for an opportunity to transfer to a female spider. The larvae can transfer from male to female when the male mates or when a female cannibalizes him.

Waiting for this propitious occasion can take weeks; indeed, they occasionally overwinter on the spider and in this time the larva takes blood meals from its host.

Once aboard a female spider, the larva takes blood meals while waiting for her to lay eggs. A wolf spider spins an egg sac of silk to carry its eggs and the larva ducks into the egg sac, which is then sealed by the female. Inside, the larva feeds on spider eggs, a feast that is a necessary prerequisite for normal development.

Then the larva spins a cocoon inside the egg sac and develops into a pupa.

A griffin has the head and wings of an eagle on the body of a lion. I have not seen one. But I have seen an animal that looks like a cross between a preying mantis and a wasp, and it sips blood from and rides on spiders.

Jeff Mitton (mitton@colorado.edu) is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.

Feb. 4, 2011