The Black and Yellow Mud Dauber Wasp (Sceliphron caementarium) is really an American species, but it was introduced into Europe in the 1970’s. It controls spider populations in houses, which is either a good or bad thing – depending on your point of view! It will rarely sting, although it looks very dangerous! The adult wasp has a 2cm-long, torpedo-shaped, body with a very thin waist and a long sharp-looking thing at the end, and there are regular bands of yellow and black which complete the threatening look.
There is at least one mud dauber lurking somewhere inside my house in South West France each summer, and hundreds of spiders (there are better things to do in France than house-work!). Despite regularly poking a camera close to these wasps no-one has ever been stung or even mildly molested - yet! The wasp visits holes in my ancient ceiling beams at regular 20 minute intervals, and whilst in the hole it emits weird high-pitched buzzing (almost squealing) noises. After a few days it usually has my whole family, and a few dubious French neighbours, observing its visits, and the clues to what it is doing mount up.
The wasp comes into the house carrying pea-sized balls, does its ‘buzzing thing’, and then goes out without the balls. These balls are lumps of wet mud it has brought up from the nearby river bank. The weird buzzing sound is made when it is fanning the mud to dry it out, and it seems to work the mud into the desired shape using its mouthparts and head as the mud dries.
Occasionally the wasp will come in low, flying slowly, and carrying something as large as itself - mostly legs by the look of it – and it turns out that these ‘large leggy things’ are massive paralysed spiders. The wasp lays one egg in the mud chamber it is making, and then provisions each egg with a ‘sleeping’ spider. When that has been done each ‘cell’ is sealed with mud and the next chamber is started. The whole thing grows to the size and shape of a cigar, and after the final sealing the wasp disappears.
This year I plan to follow the wasp down to the river and to lay there in the sun watching it collect its mud at 20 minute intervals, and maybe I'll also try to find how it gets its spiders!
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