Vol. 16, No. 36	July 10, 1997

Baby fireflies use light signals to deter predators

As children chase twinkling insects and the setting sun throws long shadows across the backyard, consider this: Light cues keep predators from snacking on baby fireflies, according to a UD study published in the current Journal of Insect Behavior.

"A flashing neon sign may lure hungry humans to an all-night diner," said Douglas W. Tallamy, entomology and applied ecology, "but the bioluminescence of firefly larvae sends a very different message to would-be predators."

The UD study is believed to offer the first laboratory--based evidence of an insect using bioluminescence--rather than coloration--as an "aposematic display," which warns predators of an unappetizing or hazardous meal. Bright colors, such as the orange an d black patterns on a monarch butterfly or the yellow stripes on a wasp, are far more typical examples of aposematic display. But, Tallamy noted, coloration offers no protection in the dark. Baby fireflies (Coleoptera: Lampyridae), therefore, use light si gnals to ward off predators, Tallamy's research team concluded.

This new insight into firefly behavior may serve as an educational tool for both adults and children this summer, Tallamy said. "The more people understand about their natural world, the more they are likely to appreciate why it must be preserved for futu re generations," he explained. "And, children who understand why fireflies are flashing may get hooked on science."

Since at least 1952, researchers have known that adult fireflies use light patterns as part of a mating ritual, Tallamy said. Because baby fireflies are not mature enough to reproduce, researchers have speculated that younger specimens might use light cue s for survival, rather than reproduction. Without laboratory evidence to support the theory, however, the messages sent by firefly larvae have remained a mysteryÐuntil now.

With John D. Pesek, food and resource economics, and graduate student Todd J. Underwood, Tallamy tested the aposematic display theory on ordinary house mice raised in a laboratory. But first, the UD researchers needed to find out whether mice think firefl y larvae taste bad.

In previous laboratory studies, vertebrate predators have consistently turned up their noses at lucibufagins, compounds present in adult fireflies. But, Tallamy said, "only anecdotal evidence suggested that larvae are also distasteful." So, mice were offe red a choice of either a firefly or a mealwormÐa delicacy for rodents. As expected, all mice rejected the bitter fireflies, Tallamy said, even when they were still hungry enough to eat more mealworms.

Next, the UD researchers tested the ability of mice to associate light with a bitter taste. At one end of a Y-shaped maze, they placed a single piece of crispy rice cereal. A second piece of cereal was soaked in a stomach-turning concoction of quinine sul phate and mustard powder before being placed on the other side of the maze, which was rigged with a light-emitting diode. Though mice initially entered the maze "with a bias toward the glowing branch," they quickly learned to steer clear of the bitter-tas ting tidbit, UD researchers said.

Within eight to 47 runs, all mice had selected the darkened side of the maze at least seven times in a row.

"Our study answers a fundamental question that entomologists have been pondering for some time," Tallamy said. It also suggests an interesting topic for discussion between parents and children, he added.

--Ginger Pinholster Art: Nurit Karlin/New York Times Graphics

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