Thursday, 12 September 2013

Its Tegenaria time again

It is evening in the late summer or early autumn and you are just settling down to watch some television when, out of the corner of your eye, you see a rather large, dark, long-legged spider dash across the room. It will be a Tegenaria species and, if you live in south-east England or the midlands it will almost certainly be Tegenaria gigantea. It will usually prove to be a male, out in search of a female or - to use the correct biological term - it is out "on the pull". In their wanderings these spiders will often end up in the bath or a sink from which, thanks to the smooth sides, they cannot escape. Today a fine specimen was in our kitchen sink. The long legs suggested immediately that it was a male; the swollen palps (the short leg-like structures at the front end) were swollen, confirming its gender.
Tegenaria gigantea in our kitchen.
Byfield 9 September, 2013

Under the microscope it will be seen that this swollen area is a very complex organ. It is a secondary sexual structure, the palps being used to introduce sperm into the female via an equally complex structure, the opening to which is known as the epigyne. The complexity of these organs, unique to each species, means that hybrids are very rare, since the swollen end of the male palp (the tarsus) must fit the epigyne with precision, rather like a key and keyhole. The epigyne is situated beneath the female's abdomen so it goes without saying that the insertion of the palp into the epigyne is a hazardous business for the male, and groups of males will meet in mid-summer for training days(Tony, stop it. You have been warned about frivolity on previous occasions.) 

I have referred to this species as Tegenaria gigantea, but in fact it is probably Tegenaria duellica. It was thus named by the French arachnologist Eugene Simon but the specimens he examined (the type-specimens) have never, as far as I am aware, been located so we cannot be sure in this matter. For this reason the later name of Tegenaria gigantea is frequently used, as these type-specimens are known and available for examination.

Several other Tegenaria species occur in Britain, one of the most interesting being Tegenaria parietina. Males of this species are particularly long-legged and, if you suffer from arachnophobia, very scary. Its common name is the Cardinal Spider, so-called because Cardinal Wolsey was apparently terrified by this species when residing at Hampton Court. It is now a scarce spider, generally confined to old buildings, and I have never found a specimen, although a contact once sent me some sent some from sacks of potatoes which had just been unloaded from the hold of a ship.

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