Wednesday, 19 February 2014

Venomless spiders

During my searches I have often seen lots of webs with many small black spiders, all within the same web. But it wasn't until I collected some and put them under the microscope that I identified them as belonging to the family Uloboridae, commonly called Venomless spiders.

Before I began my survey work I hadn't even heard of venomless spiders!


Seeing as most spiders rely on their venom to subdue their prey this made me wonder how these guys manage to catch anything. Apparently they crush their prey with many layers of silk. I wonder why any spider would evolve away from using venom when it seems to work so well? My first guess is that venom is probably very metabolically expensive to produce. So by not producing venom they actually have to eat less prey.

Also, these little spiders are often social (another rare trait for spiders), living together in multiple webs. Maybe this social interaction allows them to catch prey without venom, or maybe the lack of venom allowed them to become social (ie. they couldn't attack each other anymore!).

They are very common in Sydney, and sometimes there are many hundreds of them in one garden, but they are often overlooked. In fact, even most of the published papers about this family are from the 50's and 60's, maybe it's time for another look!

I'm pretty sure that I have only found one species so far, but there is so much colour variation that it's hard to tell.