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Symmorphus bifasciatus, a Mason Wasp

Symmorphus bifasciatus measures 7 to 11 mm in length, females being larger than males. They are black with yellow markings, but usually there are few markings. There are just two yellow dots on the thorax and the body has two yellow lines only. This way they do look rather dark.

Females make their nests in weird places. Very often old stems of bigger plants are used, such as reet, marsh thistle or blackberry. But walls or windows and pieces of wood with holes in them are frequented, including the ones people prepare for bees. A very striking place to nest in are old galls. In Britain marble galls on oak are used on the continent galls caused by flies from the genus Lipara are also reported. The nests are stashed with the larvae of several leaf beetles, mainly in the genera Agelastica, Melasoma and Phyllodecta, such as the blue willow beetle. One marmble gall may contain up to 17 beetle larvae! After she provides food for her baby and after depositing the egg, she seales off the opening to the nest. But often she is not quick enough. A whole bunch of parasites wants to profit from this meal. Especially a number of rubytail wasps, like the common cuckoo wasp (Chrisis ignita), Chrysis angustula and Chrysis viridula. But some parasitic wasps are also highly interested. And if that isn't enough quite a few very small parasites do live on the larvae of the parasites themselves. So should you ever find an occupied marble gall and take it home to see what comes out of it, don't be surprised if it is one cuckoo wasp or a whole bunch of very small parasites, in stead of the expected mason wasp!

The first adults may be seen in May, the last in October. But there is a very distinct peak in July. Symmorphus bifasciatus prefers edges of woodland and parks and is very frequently seen in gardens. In those cases it may even build a nest in an old wall. A common species all over Britain, Wales and Ireland. In Scotland as north as the Highland Region. On the continent common in Northern and Western Europe. In Southern Europe only found in mountainous regions.