Holy Ovipositor, Batman!

What am I looking at?

This is a female giant ichneumon wasp (Megarhyssa greenei, in the family Ichneumonidae). You can see its long ovipositor (1) extending downward from the last segment of its abdomen, as well as its antennae (2), which together serve to help the wasp locate insects and then lay their eggs inside them.

Click on the right arrow to see some additional views of this wasp.

Biology in the background

Ichneumonidae can be found on all continents except Antarctica. They are parasitoids because they deposit their eggs on or inside other animals, and the developing larvae feed on the host’s tissues, eventually killing the host. They mostly lay their eggs (a process called oviposition) in a variety of grubs or caterpillars, but some species exclusively parasitize spiders. These wasps’ long ovipositors can even bore through wood to get to grubs or larvae living inside the wood (as exemplified in this image). The adults typically eat sap or nectar from plants, but some have been known to feed on the fluids leaking from the host insect they have laid their eggs in.

The behavior and life cycle of this wasp is so disturbing that early naturalists like Charles Darwin had trouble reconciling what they observed with the existence of the benevolent creator that most Western Europeans at the time believed in. Darwin even wrote the following in a letter to American naturalist Asa Gray: “I own that I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars, or that a cat should play with mice.” You can read the full letter here.

Females of the genus Megarhyssa are capable of quite remarkable feats in their efforts to reproduce. First, they must locate a host deep in a woody branch or trunk; they do that by using chemical and mechanosensory cues, detecting the smell and vibrations caused by a feeding grub through their long antennae, which they press flat to the surface of the wood. Then they must insert several centimeters of their ovipositor, almost perfectly vertically, into the hardwood; the ovipositor is made of three moving parts that form a ratcheting mechanism, allowing for removal of wood dust as the tip is drilled in. The ovipositor tip is reinforced with metal, usually manganese, in a form of protein-metal ion complexes.

The largest of these wasps can grow up to 7 centimeters long, or roughly 3.5 times larger than the width of a human thumbnail, and their ovipositors can be up to 10 centimeters long, or about the length of a human palm. The ovipositor on this wasp is 6 centimeters long.

Technique

These images were created using macrophotography.