Maternal behaviour in Tegenaria

On top of a log pile under a shelf in the garden lives a large female Tegenaria. She has a large funnel shaped sheet web with a deep retreat. Every time I water the plants nearby - something I've had to do a few times in the last few weeks due to the dry weather - she jumps out of her retreat to the front to the web, only to find that there is no prey, just some water dropplets, and then she rapidly hides again. Today, I got my camera on one hand and a watering can on the other and managed to get a few close ups of the spider, which dutifully posed for me for quite a long time after being prompted by the watering. I also photographed her funnel and when I looked closely into the photo I could clearly see two tiny spiders on it.

The female Tegenaria at the front of the web

Two spiderlings at the top of the funnel (click on the image for full resolution)

Many female spiders display maternal behaviour, the most basic version consists on wrapping their egg clutches in a silky cocoon which protects the eggs from predation and adverse environmental conditions and shelters the spiderlings during their first moult. Some spiders go further than that, for example wolf spiders carry their egg sacs and spiderlings on their abdomen for a while. Tegenaria - the usual bath spider - has a different kind of maternal behaviour: the females, usually agressive and predacious towards prey entering the web, in contrast 'accept' the spiderlings on their webs for about three weeks after hatching, often longer, until these disperse. The tolerance behaviour turns into cannibalism as the spiderlings grow, but by then most of her offspring would have dispersed. Mated females lay several egg clutches in the spring - the offspring of the previous autumn males.

Females in all reproductive states - even virgin females - tolerate newborn spiderlings on their sheets, but females which are at the reproductive state when they have spiderlings are the most tolerant of all. Females rapidly approach foreign spiderlings placed on their webs but after touching them with their first legs and palps leave them alone, while they often attack and eat crickets of the same weight. The female's behavioural changes towards older spiderlings have probably to do with chemical changes in the spiderlings cuticles. Even if it seems like a very simple form of maternal behaviour, the fact that the spiderlings are able to remain on their mothers web for a few weeks is likely to dramatically reduce their chances to fall prey to predators.

More information
Pourie, G., and Trabalon, M. (1999). Agonistic behaviour of female Tegenaria atrica in the presence of different aged spiderlings Physiological Entomology, 24 (2), 143-149 DOI: 10.1046/j.1365-3032.1999.00124.x