Spiders work together to leap onto their prey and bind it fast with strands of silk (Image: Leticia Avilés) Females guard their egg sacks on the underside of a leaf (Image: Leticia Avilés)

Spiders are not famous for their caring, sharing nature. Unlike insects such as ants, it is virtually unheard of for arachnids to live in societies that employ tactics and team work.


So the discovery in Ecuador of spiders nesting in family-based communities and hunting in packs was a surprise find for Leticia Avilés, an arachnid expert at the University of British Columbia in Canada.

According to Avilés, 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.

Size differences

The spiders carry their kill back to the nest and share it with all of the others in the community. “It’s truly remarkable,” says Avilés. “Not only do the spiders cooperate during the kill, but if the prey is large they take turns carrying it back.”

However, there is a lot that is still unknown about the species.

Avilés discovered vast differences in colony sizes. Most colonies were just a few dozen spiders, but occasionally a colony population would soar into the thousands, declining to multiple small colonies again within days.

“We have no idea what controls the sizes of these colonies, but what we do know is that they must have unbelievably high reproductive potentials to achieve such large populations so quickly,” Avilés told New Scientist.

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.

Journal reference: Biotropica (DOI: 10.1111/j.1744-7429.2006.00202.x)