The wiles of spiders are varied and infamous. They use disguises, snares, poisons and a variety of acrobatic jumps, swings and darts.
The latest cleverness to be deciphered, and published in the May 22 Science, is that of the bolas spider, which has two tricky wickets -- one chemical, one physical -- to capture hapless moths.
These spiders have simple webs that at first glance would not seem useful. The spider tacks up one thread, horizontally, and descends like a trapeze artist from the middle of the wire. Swinging below, the creature holds a short line that resembles the South American cowboy weapon, the bola. At the end of the line is a glistening glue ball that the spider flicks at passing moths.
An accuracy of about four strikes in 10 throws prompted one researcher to name one species Mastophora dizzydeani, after late major league pitcher Dizzy Dean.
The two striking facts about this method of hunting are that the spiders are able to lure moths close enough to strike and that the victims are all male.
Mark K. Stowe and colleagues at the U.S. Department of Agriculture's laboratory on chemical attractants in Gainesville, Fla., set out to prove a long-held suspicion that the trick was one of sexual attraction.
The researchers coaxed spiders to do their high-wire act in a small chamber, from which air was drawn to be analyzed chemically. They then compared the odors produced by the spiders with the sexual chemicals, called pheromones, given off by female moths to attract mates.
They found that the spiders were giving off three of the moths' sex attractant chemicals to lure unsuspecting male moths within range of the spiders' deadly pitch. Further, it appears that the spiders can mix and match the sex attractants of many species of moth.
"In the field, the spiders prey on male moths of 19 species, with single individuals catching up to nine species . . . . Records indicate that individual spiders often catch two or more moth species with apparently incompatible pheromone blends," according to the Science article.
Thus, the researchers suggest that spiders are able not only to put on the odorous veils of a single female moth, but may be able to pose as a whole harem.