Tuesday, 7 September 2010

Sceliphron - Potter Wasp

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 Any house owner would be surprised by a row of tiny clay pots lined up inside a fold of a curtain. When they knock them off and find the shards spilling out dozens of apparently dead spiders, they may be appalled. The culprit is the female of a wasp with an exceedingly narrow waist, which, no doubt with huge labour, constructed all the pots and stuffed them with a hundred spiders in less than half a day. Just imagine the journeys needed to collect the wet mud, and the spiders!
If the householder should find the adult wasp [at towards 2 cm long it is somewhat alarming], and hopefully has an inquiring mind, he or she might ponder- ‘With a waist like this, how does any food pass from front to back?’ Perhaps nothing does. I will come back to that mystery. But here we have an example of a creature which was first found in Europe (Austria) in the 1990’s. Since then it has invaded much of Northern Italy, southern France, Spain and parts of Central Europe, but its original home seems to be from near-Asia . This year it has been found in Paris and near Cahors and in Les Landes. It looks as though it will colonise all of France. This species may be an invader but there are various indigenous relatives not dissimilar. In this instance you will see that the waist is black and the abdomen has yellow bands. Some indigenous relatives have bright yellow waists and totally black abdomens or are otherwise marked. These most particularly occur in southern regions.

You can call it a potter-wasp. Inside each pot the adult lays one egg and then fills the pot with between 6 to 12 tiny spiders, paralysed with a nerve poison. The developing larva gradually eats the paralysed prey, starting with the abdomens, and in about a month will convert into a pupa and then into the adult.
Can that narrow waist ‘the petiole’ contain the gut, a blood vessel and a nerve? It is plain that no solid food can pass through it. It seems unlikely that anything much passes through it. It is as though the structure is little more than something like a tow-bar on an articulated lorry. The front end does the moving, getting energy from the sugar rich nectar which it consumes. The rear end is effectively no more than a reproductive structure, stuffed with eggs, rather as the lorry’s articulated trailer is stacked with goods. This ‘trailer’ will have nerve ganglia and possibly they control the reproductive activities. The adult insect has finished growing and has no need for anything much in its diet except energy, i.e. sugars.

1 comment:

Anonymous said...

Last year over a period of a few weeks I had one of these making his pottery under my pillow. Every night I'd have to carefully remove his work, and every morning I'd put it back as best I could, and on several occasions he'd added 'pots'. It was really fascinating!