According to New Scientist a new species of spiders has been discovered that lives in groups and cooperates when hunting:
According to AvilÃ©s, there are over 39,000 identified spider species. While she has seen just over 20 species cooperate, she has never encountered any species quite like Theridion nigroannulatum.
The spiders live in nests that house up to several thousand individuals which hunt by hanging threads from low lying leaves. They then hide upside down, beneath the leaves waiting for prey.
When an insect flies into the strands a group of spiders drop down and throw sticky webbing over it. To finish off the ambush they inject venom with their tiny jaws.
After the kill is made the spiders take turns carrying it back to the nest, which can be composed of anywhere from a few dozen to thousands of spiders (there seems to be a boom and bust cycle going on, which makes me wonder). The interesting thing is:
A further mystery is why the female spiders come in two different sizes. Among social insects, when females differ in size it is due to a division of labour. Bees are a classic example: large females lay eggs and small females search for food. With spiders this has not been observed before – T. nigroannulatum could be the first.
Here is a picture (also from New Scientist):