Pulse of the Planet

Redback Spiders: Mating Sacrifice

For Redback spiders, mating begins innocently enough with the male courting the female by plucking on the strands of her web, producing a vibration which has been translated into sound in this recording.

For Redback spiders, mating begins innocently enough with the male courting the female by plucking on the strands of her web, producing a vibration which has been translated into sound in this recording. But the male is also courting death: as the two spiders mate, the female will slowly consume her partner. So does he try and escape? Hardly. Instead the male spider somersaults his body into position directly over the female's mouth, as if to say 'digest me, I'm yours!'

Maydianne Andrade is a graduate student at Cornell University, where she spends much of her time in a small humid laboratory filled with spiders and insects. It's here that she's had a chance to study the ways that Redback spiders make the most out of a single mating.

"It's amazing to watch because its clear that the female is not doing anything to force the male to do this, rather the male is doing this sort of sacrificial somersault all by himself. The fangs of the female then sink into the male and she begins to extrude digestive enzymes and basically begins to eat the male while he's copulating with her."

After he's copulated with the female for, let's say, between two and 25 minutes, he pulls himself loose of the female, then he gets back on the web, courts the female again, for this time much shorter, around 10 minutes or so. Then he climbs back onto her, somersaults again, and during and after this second insertion, she'll kill him completely- in about 65 percent of the cases." Now if spiders ever underwent therapy, you can imagine what incredible material their analysts would have to work with! In any event, scientists think this sort of self-sacrificial behavior actually increases the odds of the male spider's producing more offspring.

In case you're interested in how the recordings of such subtle vibrations were made: "The techniquethat allows us to hear the vibrations the male is using involves reflecting a laser beam off a small glass bead that's placed on the web. If you can imagine this bead sitting on a string, when the string is vibrated, the bead will move back and forth along with the string. And when the laser beam reflects off this bead and is recorded by a computer, essentially, that computer can translate the movement of the bead into information that tells us what types of vibrations were moving through the string. From looking at these patterns of starting and stopping vibration and how closely synchronized they are, we think we will be able to get information about what the males are signaling to each other as well as to the female."

PHOTOS: Courtesy of Maydianne Andrade.