Airdate: Jan 30, 2004
Scientist: Maydianne C.B. Andrade
For Redback spiders, the web is an extended sensory organ.
ambience: Male redback spiders, web vibrations
We're listening in as two male spiders compete for the attentions of a female spider in what's thought to be a rhythmic showdown. I'm Jim Metzner, and this is the Pulse of the Planet.
These are Redback spiders, an Australian species which spends most of its life on its web. For Redbacks, the web is an extended sensory organ. It allows the spiders to detect the presence of prey and other spiders through the vibrations which ripple through its surface. In this recording, two male spiders pluck at the strands of a female's web in a gesture which scientists still don't fully understand.
"And it's clear that even though these males are very far apart and don't see well, that the first male recognizes that the second male has been introduced, because they will both stop their movements at the same time. Quite often then, one of them will begin to move again and then the first competitor will either lunge towards the second, or begin his vibrational movements in a more sort of frantic way than he was before."
Maydianne Andrade studies the communication signals of Redback spiders. She listens in on their vibrations with the help of laser technology.
The technique that 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 and 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."
Pulse of the Planet is presented by the National Science Foundation. I'm Jim Metzner.