The Webmasters

By Cassie Ferguson

Gazette Staff

It's hard not to anthropomorphize when it comes to spiders. Were they human, their mechanisms for deceit would rank them beyond Iago and Richard III, and make Lady Macbeth appear rather tame.

Spiders have turned to trickery not in imitation of human malice, but as a result of what Catherine Craig describes as a 300-million-year evolutionary war against their prey.

Initially attracted to spider webs by their translucent shimmer, Craig, a research associate at the Museum of Comparative Zoology, has been caught up in nine years of researching the evolution of spider silk.

"Getting insects to fly into a web is pretty tricky," she says. "So spiders have evolved to put up an amazing variety of nets."

That's saying they do far, far more than install cobwebs in a high corner and hang out until some hapless no-see-um buzzes by.

Some spider species, reports Craig, have evolved to contain miniature textile factories in their abdomens. One, called Nephila clavipes, can weave many types of thread, using its legs to pull liquid silk from its several silk glands. If Nephila pulls quickly, the strand will be strong; slowly, and the line will be fragile.

What Craig finds really remarkable about Nephila is that it can spin "liquid gold" to help it capture bean-sized bees. In the 1980s, researchers discovered that the spider adds yellow pigments to its silk. In an experiment done two years ago, Craig and her colleagues found that when set against a bright background such as the sky, bees are attracted to the web by its golden color. But against a leafy background, the color camouflages the web, making it difficult for bees to see.

Another spider that's captured Craig's attention is Argiope argentata. She found that Argiope spins a translucent web, with dense white zigzags that mimic the ultraviolet pattern reflected by a flower. Lest the bees that feed on the flower learn to avoid the web, the spider varies the zigzag patterns.

"If a bee that's escaped from a decorated web sees a web decorated the same way, it won't fly into it a second time," says Craig. "So the spider has evolved to change the pattern, some days changing the number of lines and their orientation."

Some spiders, says Craig, have learned to take a more active role in using their silks to capture their prey. One, called Epeirotypus, will construct a circular web, then attach a line to its center. The spider grabs the line and pulls the web back into a cone invisible to insects. When the insect flits into range, the spider lets the line go, flinging the spring-loaded net at its prey.

Some spiders have lost their ability to spin webs, says Craig. But they still use their silk to trap their prey. In an article on the evolution of arthropod silks Craig wrote last year, she cited a type of silk produced by a spider called Mastophora. According to a study in the journal Science, Craig noted, the spider perfumes the air with a scent that mimics that of a female moth. When a male moth looking for love shows up, the spider beans it with a ball of sticky silk.