Petioles and Gasters

The Gold-marked Thread-waisted Wasp/Eremnophila aureonotata has a particularly long example of a “wasp waist.” This is also called the petiole, a word also used in botany for the stalk that attaches the leaf blade to the stem. Some definitions place the wasp petiole between the thorax and the abdomen, but anatomically it’s actually considered the first part of the abdomen. The bulbous portion of the abdomen is technically the gaster.

Here’s an Elegant Grass-carying Wasp/Isodontia elegans. Note the petiole’s curve, a characteristic of Isodontia.

Here’s another I. elegans. Looks like she’s been in a fender-bender.

These deformations of the gaster are the work of female parasitic Twisted Wing Insects, order Strepsiptera. (A whole order I wasn’t even aware of a few years ago! They seem to be most related to beetles.) The females live inside their hosts, in-between the plates of the gaster. Paraxenos auripedis in particular is associated with Isodontia wasps.

Here’s another Elegant.