HYMENOPTERA > APOCRITA | Parasitica > Trigonaloidea > Trigonalidae

Trigonalids are extremely rare with only one known European species, Pseudogonalos hahnii.

The last official record from England was back in 1998, and it has only been officially recorded a handful of times since then, mainly from Wales or Scotland. It is rarely collected, and has never been found in Ireland. There are very few photographs in existence of a live adult, which makes my find even more remarkable, or perhaps I should say lucky, as I'd only taken an interest in photographing wasps a few weeks before!

After having the identity confirmed, I learnt that whilst superficially similar to species such as black spider wasps or some small ichneumons, they are easily separable by a combination of characters. The most noticeable features, both in the field and when looking at photos, are the long antennae with 26 or 27 segments and characteristic forewing venation with 10 developed cells and well-formed costal cell.

Pseudogonalos hahnii is a hyperparasitoid wasp with an unusual and complex biological strategy where the female lays her eggs on foliage in the hope that they will be consumed by sawfly or lepidopteran larvae and then for that host to be parasitised by a primary parasitoid before it can complete its development. Interestingly, the trigonalid larvae will develop to adulthood regardless of whether the secondary host was parasitised by the primary host species before or after it ingested the trigonalid eggs. This is possible as the larvae can remain viable for several months if necessary, waiting for a suitable ichneumonid parasitoid female to oviposit into it.

When the adult wasp finally emerges it will have a very short life span, that rarely lasts more than just a few days, which is the main reason why the species is so rarely seen or collected by entomologists. The timing is impossible to predict so, as far as I'm aware, you can't go out specifically looking for these species. You just need a bit of luck by being in the right place at the right time.

Updated, March 25 (v.2)