Various Solitary Wasps in the Garden

15th August 2012
I've been seeing various examples of "solitary" wasps in the garden recently. By "solitary", I'm referring to those that do not live in social aggregations, as do the Common Wasp (Vespula vulgaris), the Hornet (Vespa crabro) and their relatives.

The classification of the Hymenoptera is somewhat complicated (for non-entomologists like me, anyway). The Hymenoptera is divided into two suborders, the Symphyta (Sawflies and their relatives) and the Apocrita (species with a thin "waist" including all the wasps, ants and bees). Within the Apocrita, there are two groups; the Parasitica (the most diverse of all Hymenopteran groups and including Ichneumons) and the Aculeata, species that have modified their egg laying tube (ovipositor) into a sting. This groups includes ants and what we typically think of as bees and wasps. You will often see these referred to as the Aculeate Hymenoptera or just Aculeates. So much for the scientific stuff!

The image above left is one of the aculeates; a Mason Wasp of the genus Symmorphus. This one was searching my garage wall; presumably looking for a possible nest hole. Symmorphus wasps nest in plant stems or holes in walls or in banks. They prey on other insect larva (mainly leaf beetles) which they sting, paralyse and then use to provision their nests. The Symmorphus larvae use the prey as a food source. The wasps are in turn, parasitised by species of ruby-tailed wasps (jewel wasps), which search out their nests and lay their own eggs. I saw a ruby-tailed wasp searching the wall at the same time!

Another aculeate; this is a wasp in the genis Trypoxylon. I've not seen these in the garden before. Trypoxylon wasps (there are five species in the UK), have elongated abdomens and they nest in hollow plant stems and in holes in dead wood. Interestingly, they prey on small and immature spiders which like the Symmorphus wasps, they use to provision their nests. This one was small (about 7-8mm). The many varieties of small wasp can be rather inconspicuous and easily overlooked. Until a few years ago, I'm not aware of ever seeing them. Because I've now developed an interest in bees and wasps and I'm always on the lookout with my camera, I seemed to have "got my eye in" and see them all over the place!

The final image; bottom left, is an Ichneumon Wasp - Diplazon laetatorius. Ichneumon wasps are sometimes (incorrectly) referred to as Ichneumon flies. It's because I included this one that I mentioned the classification details. Ichneumons are included in the Parasitica.

One of the ways they differ from wasps in the Aculeata is that rather than provisioning nests with their "prey"; they just lay or inject their egg(s) on/in it. Often, some venom is also injected along with, or just prior to, the egg. This venom can be used to temporarily or permanently paralyse the host and to also modify the host's tissues. This can make the host more nutritious for the developing wasp larva and also help disable the host's immune system. Rather than parasites, these parasitic wasps should more accurately be referred to as parasitoids. That is because they will eventually kill their hosts. Parasites just benefit at their host's expense. Some of the common manifestations of wasp parasitoid behaviour include multiple wasp larvae erupting out of the body of "Cabbage White" butterfly caterpillars (I remember being horrified when I saw that as a child) and the empty aphid "mummies" that can be seen on plant leaves. All rather grisly stuff!

Thanks to DavidNotton and Norwegica on iSpot, for assistance with identification.

[Click on any image for a larger version]

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