Huge Eyes Help Net-Casting Spider Catch Crawling Prey

Posted on May 26, 2016

Deinopis spinosa net casting spider

The net-casting spider has the largest eyes among all known arachnids. University of Nebraska-Lincoln biologists have determined that the nocturnal spider species, Deinopis spinosa, puts these eyes to use when catching crawling prey.

The net-casting spider uses a rectangular band of silk to catch prey while rappelling down from a single thread of silk. It can catch prey by lunging forth and engulfing prey in the stretched-out net. This spider does this rapidly in about one-thousandth of a second.

The researchers wanted to know how much the spider was benefiting from its big eyes. They used a silicone blindfold to cover the spider's massive secondary eyes that are about 2,000 more light-sensitive than human eyes. With its big secondary eyes blocked the spider was still able to catch flying prey at the same rate. However, it failed to catch walking prey on the ground. The researchers say none of the blindfolded spiders were able to snare a walking meal while their vision was impaired.

Jay Stafstrom, who co-authored a new study with faculty adviser Eileen Hebets, said in a statement, "(The spiders) can still catch things out of the air (without those eyes). Why are they, presumably, investing so much in these large eyes? One of our hypotheses is that it's because there's a lot of prey on the ground, and by having vision in these enlarged eyes, not only are they getting things off the ground, but those things are bigger and probably more nutritious."

A research paper on the study was published in the journal Biology Letters. If you are curious, LIveScience has a good photo of the net-casting spider's enormous eyes here. Here is a video of the spider in action:

Photo: Jay Stafstrom

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