When the going gets tough, some spiders make friends

“A lot of fun, and new and exciting.” That is what Catherine Hoffman, a graduate student in Dr. Leticia Aviles’ lab, said it was like working in Ecuador. Aviles is a professor in the department of zoology.

However, working in the field has its challenges. Cell service is hard to come by and Hoffman had to adapt to continuous rainfall for three straight days in the rainforest. She was up to the challenge of being “forced to think of new ways to do things when your plan A and plan B don’t work out.”

Having worked with Anelosimus spiders for a long time, Aviles and Hoffman observed less social species found at higher elevations and more social species found at lower elevations. Social spiders are those that live in giant, cooperative webs (think five-metre long webs).

Aviles and Hoffman knew that a relationship existed between prey size and elevation — bigger prey were found at lower elevations, while smaller prey were found at higher elevations. This relationship explains why social species are not able to survive at higher elevations because there aren’t enough large prey to sustain them.

The question that Aviles and Hoffman wanted to answer was why these sub-social species could not live in these lower elevations.

While some previous work had been done to examine this trend and started to answer this question, Aviles and Hoffman conducted an experiment to effectively demonstrate this connection.

According to Hoffman, there have been a lot of previous studies looking at where social spiders lived, and compared factors like rain, temperature or humidity to predation and prey availability.

But all of these studies just observed a pattern — no one had put it to the test yet. That’s what made Hoffman’s study unique — their experiment could test the influence of where spiders live.

Hoffman and the research team took Anelosimus spiders from the higher elevation and kept half of them at their normal elevation. The other half was moved to a lower elevation. At the lower elevation site, Hoffman and the research team removed rain and predation, and observed how those factors affected Anelosimus spider survival.

The sub-social species did better better at higher elevation than at lower elevations.

However, after monitoring the spiders for around a month, all of the colonies had died — the transplanted spiders did not survive when moved to a lower elevation. Additionally, rain and predation had no impact on survival of the spiders who remained at the higher elevation.