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Spiders Get Flashy at Night to Lure Prey

Jennifer Viegas, Discovery News

Photos

Dazzling and Deadly

Oct. 31, 2007 -- Nighttime is the right time for many spiders, according to a new study that found certain species flip themselves over at night in order to display otherwise hidden abdominal stripes that lure unsuspecting prey.

The discovery explains why arachnids like the giant wood spider and the orchid spider have been observed eating large amounts of carefully wrapped prey on their webs just before sunrise. It also suggests that entomologists may have underestimated the activities of some spiders when darkness falls.

A clue to detecting night-prowling spiders is coloration. Dark grey or brown spiders usually are nocturnal, since their drab colors serve to reduce their visibility during the day. Many spiders, however, have different patterns and colors on their abdomen. Neoscona and Araneus from East Asia, for example, possess either yellow stripes or yellow spots in this area.

"During the day, these spiders usually perch on twigs or barks near their webs with their brown-colored (back side) facing upwards and the yellow abdominal markings obscured," determined study co-authors I.-Min Tso, Jen-Pan Huang and Chen-Pan Liao of Taiwan's Tunghai University.

"However, at night while the spiders are sitting on their orb webs hunting, they fully expose the yellow markings," they added, explaining that other studies suggest moths may perceive such colorful markings as potential flower, or new leaf, food sources.

For the study, the research team focused on brightly colored orchid spiders, which have green bodies, silver stripes on their backs and yellow or bright green stripes on their abdomens.

The team at first monitored this spider's hunting behavior with video cameras 24 hours a day. They found that the number of active night hunters was "two to three times higher than (those orchid spiders that hunted) during the day." Their snagged prey -- mostly moths -- tended to be bigger at night too.

The scientists experimented with various color manipulation tests that involved painting over the silver, yellow or green parts of the orchid spider. Obscuring the yellow stripes considerably reduced moth catches, providing evidence that these colors probably function as night lures.

The findings have been accepted for publication in the journal Animal Behavior.