Tuesday, 6 October 2015

Pholcidae: cellar spiders

The Pholcidae is a large family of spiders, although most of the family's diversity is in dry temperate or subtropical regions, where they can live in diverse habitats away from houses. In our latitudes, these warm loving spiders live in caves, cellars, wells, outbuildings, and houses. The most common and widespread species in the UK is Pholcus phalangioides - a male with his rounded palps is on the top photo-, which has also now been introduced in other regions of the world, including North America, from its native Eurasian range. There are several common names for this spider, one of them, daddy long legs, is certainly confusing, as it is also applied to crane flies and harvestmen. They like to build their almost invisible tangled webs on ceiling corners, from which they hang upside down looking like thin chandeliers. Their legs are, indeed amazingly long and thin relatively to the body.
The natural history of Pholcus phalangioides is easy to study, as they don't move much, residing for weeks on end motionless on quiet corners of the house, and are present year round. 
A pair mating. Mating can last more than an hour. Males are slightly larger (10 mm) than females (9 mm).
Mummy long legs
As many other spiders, Pholcus take extended care of their offspring. They hold their eggs with their chelicerae until they hatch. The egg brood is kept together by a few silk threads.
A gravid Pholcus, she laid eggs the following night. She resided under the outside toilet shelf.
Here is the same individual with her newly laid eggs.
These eggs are going to hatch soon. The linear whitish patterns in the eggs are the legs of the developing young.
In about two to three weeks, spiderlings hatch. Right after emergence, the spiderlings remain together for a few hours, before moving onto the mothers surroundings.
The Pholcus under the shelf, with her record number of offspring, I counted 65 (30 is the average).
Pholcus mother with her meal, another spider, surrounded by her offspring. She will set her egg sac aside to feed or to mate, and may lay further egg batches after the young spiderlings have dispersed. These spiderlings are almost ready to disperse, having had their first moult.

Spider hunters
Despite their fragile, spindly appearance, Pholcus are fierce predators, and regularly hunt other spiders, often much larger than themselves, including house spiders (Tegenaria) and woodlouse hunters (Dysdera). They achieve this by quickly wrapping the other spider on silk using their long legs, which allows them to keep their distance. Once thus subdued, they bite their prey. Pholcus uses a sit and wait approach, which is probably very successful during the autumn, when male house spiders move about in search for females. They can also use an ambush approach, moving about and, when it finds another spider's web, it will make it vibrate to attract the owner.
They don't always succeed in spider hunting, through, and I have seen other spider, the mouse spider (Scotophaeus blackwalli) with the remains of a Pholcus
Another successful Pholcus with prey spider.
Pholcus with woodlouse.
A Scotophaeus blackwallii with captured Pholcus.

1 comment:

David Breslin said...

Last summer I was obliged to remove a nest of cellar spiders from the middle of an exposed wall at work. The spiderlings were more than half-grown. To my surprise, the mother attempted to stay and defend them against me, crouching at bay rather than retreating. I felt a bit bad about evicting her, but most of the spiderlings survived- they kept turning up in odd corners for weeks.