Biology & Environmental Studies Professor Featured by NSF

Professor George Uetz is being featured on the National Science Foundation's web site this week in the following article:

Spider vs. Fly: Specialized Deception, Attack and Defense Rule the Conflict

It seems quite simple: Spider spins web. Fly gets caught in web. Spider spins silk lunch box around fly, feasting on the treat at a later time. End of story.

Not so, according to scientists studying the relationship between some spiders and flies under a National Science Foundation research award. It's more of a full-blown engagement involving specialized attacks, defenses, and purposeful deception.

Biologist George Uetz and fellow researchers examined the postures of the social orb-weaving spider, Metepeira incrassata, in relation to the sarcophagid fly, Arachnidomyia lindae (a specialized predator of Metepeira spider eggs) and the non-predatory domestic housefly, Musca domestica.

The study, published in the journal Behavioral Ecology and Sociobiology, suggests that a highly specialized predator's attacks may cause the evolution of predator-specific defensive responses in the prey.

Most spiders live a largely solitary existence, but a handful of species like the orb spider Metepeira live in social colonies. The sarcophagid fly attacks egg sacs at the spider colony and deposits a larva on the egg sac surface. Developing larvae eventually eat the eggs inside the sac.

The researchers noted that when a spider guards its egg sac against the sarcophagid fly, it assumes specific defensive postures to counter the fly's attack. This defense differs from responses to attacks by other flies.

When the researchers presented a domestic housefly to the spider, it was recognized as non-threatening. The researchers believe this response results from the spider's ability to distinguish between the sarcophagid fly's wing-beat frequency and the wing-beat frequency from a domestic housefly. This behavior can be likened to soldiers being able to distinguish a two-bladed helicopter from a three or four-bladed helicopter and adjusting their response accordingly.

But the story doesn't end there. The sarcophagid fly may pluck the spider's web to imitate the vibrations of captured prey, a ploy that tricks the spider into letting down its guard. In turn, the spider may cut the web thread relaying this distracting information, thereby preventing a lapse in defense of the valuable egg sac.

"What's neat about this is the number of ploy-counterploy interactions that have evolved," said Michael Greenfield, director of NSF's Animal Behavior Program. "Here, the interactions go back and forth as many as four times, a striking level of complexity in the realm of predator/prey behavior." [Manny Van Pelt]

If you would like to speak with a science expert on this topic, please contact Michael Greenfield [(703) 292-8421 / mgreenfi@nsf.gov] or Steve Vessey [(703) 292-8421 / svessey@nsf.gov]

See

www.nsf.gov

for more details.