Spider courtship is risky business. One wrong move by the male, and he becomes a tasty lunch to a passing predator.
The complexity of spiders has long fascinated Dave Clark, an animal behavioral scientist at Alma College. He uses virtual digital technology to study animal communication, most specifically the wolf spider (Schizocosa ocreata).
In a recent study published in the scientific journal Behavioral Processes, Clark along with researchers George Uetz from the University of Cincinnati and Tricia Rubi from the University of Minnesota found that the extravagant courtship dances by male wolf spiders make them highly susceptible to predators.
“Female spiders are pretty stationary; they generally stay within a square meter area,” says Clark. “But males wander several square meters in search for females. As they wander, they are at risk of predators, such as other spiders, toads and birds.”
For their research, Clark made videos superimposing images of stationary, walking and courting male spiders on a digital version of a leafy natural habitat. The videos then were shown to a group of captive blue jays, a natural spider predator. The birds were trained to peck at buttons to indicate whether or not they saw wolf spiders on the screens.
The blue jays responded to the videos in the following ways:
- The birds had difficulty spotting spiders that were motionless on the digital screen. Because of their natural markings, the spiders blend into the leafy background. “Spiders have learned to freeze in place as a defense mechanism against predators,” says Clark.
- The birds had less trouble seeing non-courting spiders that were simply walking through the leaf litter. “Males are not always courting; sometimes they wander looking for female silk,” says Clark. “But once a male finds silk, the male knows that a female is nearby and so begins to court. A female will eat a male who is walking by and not courting.”
- The blue jays were quick to find male spiders engaged in their ritual courtship behavior. “Once a male spider starts courting, the birds locate them quite easily,” says Clark.
“Female spiders select their mates for the males’ various decorations,” says Clark. “The bristles or tufts on their legs are attractive to females, and so the males show them off in courtship. The males’ vigorous leg-tapping courting behavior also is attractive to females — as well as to potential predators.”