Mantids are often thought of as apex predators of the insect world. Once grasped in a mantid’s tough forelegs, not many insects have a chance of escape. Yet mantids are quite vulnerable themselves when starting off in life. Female mantids lay eggs in masses called oothecae, which they glue on to hard surfaces. In a few cases the female will stick around and protect the eggs and hatchlings, but in most species she will simply abandon her eggs to their fate. The foamy material that surrounds and encases the eggs is a formidable barrier to predators. Typical predators like ants or birds rarely bother to try. But to small parasitoid wasps, no barrier is impenetrable.
While in Arizona this past spring, I collected an ootheca of the California mantid, Stagmomantis californica, with the intention to send it to a researcher working on U.S. mantids. Unfortunately, this particular ootheca had a different fate. A few days afterward, I looked into the container to discover a horde of little wasps in the container. The mantid ootheca was riddled with tiny emergence holes. Closer inspection revealed something interesting – there was more than 1 wasp species! Shiny, black-gold-green creatures with ovipositors twice their body length flitted back and forth; flattened orange wasps with white stripes and bug-eyes scampered across the walls; and a lone, very tiny, black-gold insect with striped legs was skittering helter-skelter between all the larger wasps. It was a veritable ecosystem that had emerged from this one mantid ootheca – remarkable.
Photographing these wasps was a challenge. Taking the lid off the container would have meant losing them all, so I was forced to freeze the container for a minute to stun them all temporarily – not my favorite technique, but in this case it was required. Individually they were a little better behaved, but not by much. It took me a week to find the time to upload the photos to BugGuide, but it took only hours for Ross Hill to identify them all. It turns out that the dark species with a long ovipositor was a member of the genus Podagrion (Torymidae), which are all obligate parasitoids of mantid oothecae. The flattened orange critters were Anastatus semiflavidus (Eupelmidae), a generalist which is known to parasitize a number of insects including stinkbugs, giant silk moths, and mantid oothecae. And the solitary striped-leg species? A pteromalid, many of which are hyperparasitoids (basically, a parasite of a parasite). My suspicion is that this wasp parasitized a larva of one of the Podagrion or Anastatus, but that is just a hunch. Incidentally, several of the wasps lived in captivity for almost 2 weeks, much longer than I usually expect wasps to live. Perhaps that’s more standard in the dry, unpredictable desert habitat where they came from.