Here’s another fascinating leaf-bothering find, this time on a willow leaf, found during a recent wander around Cardiff’s Cathays Cemetery. I was fairly sure, from their size, shape and number, that these were Green shieldbug eggs and, as their colour had changed from the usual green, that the eggs had been parasitised. And, of course, that led me to wonder whether the tiny wasp might be the parasite.

At home, my online research didn’t come up with anything in the UK but I did find information on the website of American Utah State University about ‘two families of stink bug [the American name for shieldbug] parasitoids in Utah, Eupelmidae and Scelionidae.’ The webpage provided information on and images of the two wasp genera and, from that, I decided the Scelionidae looked most promising, and that my wasp looked very similar to the Trissolcus species shown there.

The website entry explained how the parasitic wasp lays its eggs in the shieldbug eggs, where the wasp larvae hatch, eat their hosts, and eventually pupate. Also,

There is usually a skewed sex ratio in emerging wasps. In a typical stink bug egg mass that consists of 14-28 eggs, one to three wasps will be male, and the rest will be female.
Male wasps will emerge first and wait for the females to emerge. Once mated, the females fly off in search of new egg masses to sting.

That behaviour, of the male wasp waiting by the parasitised eggs for a female to hatch, fitted with what I had observed. Despite me carefully turning the leaf this way and that to try to get better light and closer photos, the little wasp didn’t fly off – now I knew why.

Later, after I’d posted photos and my speculation on social media, my identification of this being a Trissolcus sp. wasp was confirmed by a wasp expert on Bluesky, though I haven’t yet had official verification of my record.