A wasp built like a needle
On July 20 in Rhode Island, a long, thin wasp drifted onto a leaf in front of me and folded its wings, and for a moment I thought a pine needle had landed there. Then the needle walked. Slender beyond reason, with a thread-like waist and an abdomen that tapered to a fine point. It sat in the sun for a minute, antennae working, then launched itself into the grass as suddenly as it had arrived.
It was Acrotaphus wiltii, an ichneumonid wasp in the family Ichneumonidae, order Hymenoptera. Ichneumonids are parasitoids: the females use a long ovipositor to lay eggs on or inside other arthropods, and the larvae develop by feeding on the host, which sounds grimmer than it is. From a gardener’s perspective, these wasps are free pest control.
Species in this genus have been recorded as parasitoids of orb-weaving spiders, and the females are known to track down their prey in the web. That long ovipositor is not a stinger; it is an egg-laying tube, and the wasp is generally not interested in people at all. In the wild, ichneumonids like this one are part of a quiet web that keeps caterpillar and spider populations in balance, and a garden with a healthy wasp population is usually a garden with fewer pests.
The family name comes from the Greek ichneumon, meaning tracker, a name the ancient Greeks also gave to the mongoose, because both are hunters that track their prey with skill. A tiny needle-bodied tracker, working the margins of a Rhode Island field, and I was glad to have met it.
