December 2014 Featured Paper

"Do Courtship Flashes of Fireflies Serve as Aposematic Signals to Insectivorous Bats?" by Paul R. Moosman Jr., Christopher K. Cratsley, Scott D. Lehto, Howard H. Thomas. Animal Behavior, Volume 78, No. 4 (October 2009), pp. 1019-1025.
Read the Original Paper. (Subscription to ScienceDirect is required. Check your local university library for access.)

Scientists believe that bioluminescence in fireflies originated as a warning signal in the larvae. Larval glow served to warn off predators, announcing the firefly’s unpalatability. Only later did bioluminescence evolve as a mating signal among adult fireflies. However, this adult flashing may have other consequences as well, both harmful and beneficial. The flash provides some predators a means of locating their prey. Predatory Photuris fireflies imitate female Photinus to lure Photinus males into their grasp. At the same time, predators who have learned from experience that the chemical defenses of fireflies make them unpalatable are warned off by the firefly flash.

This study investigates the relationship of fireflies to three common species of bats to determine:

  1. If bats and fireflies occupy the same area
  2. If fireflies are found in the bats’ diet
  3. If fireflies’ chemical defenses make them unpalatable to bats
  4. If a firefly’s flash affects the likelihood of a bat attack

In the area studied, three species of bats were commonly found cohabiting with fireflies: the little brown bat, the big brown bat, and the northern long-eared bat. Beetles made up a large part of their diets— about 20% of the diets of the little brown bat and the northern long-eared myotis, and 80% for the big brown bat. That suggests a strong likelihood that bats will prey on fireflies. However, an inspection of the fecal pellets, or droppings, of the bats found no firefly remains. Bats in the wild seemingly do not feed on fireflies.

But what makes fireflies the exception? To test whether the bad-tasting protective chemicals in fireflies discourage bats from eating them, mealworms were coated with an extract of firefly. Mealworms coated with an extract of mealworms were used as the experimental control. After tasting a firefly-coated mealworm, the bat rejected it, followed by coughing, head-shaking, and sneezing. The control mealworms were always accepted and eaten. So the chemical defenses of fireflies seem to be an effective protection against predation by bats.

Do bats reject a firefly only after first attacking/tasting it, or does the flash of the firefly warn the bat that this will be a bad-tasting meal? To test whether bats avoid a flashing prey, the bats were exposed to a flashing lure designed to imitate a firefly in flight.

Results were mixed. The big brown bats were less likely to attack flashing lures than non-flashing lures, so the flash apparently did serve as a signal to avoid making contact with the fireflies. The little brown bats and the northern long-eared bats, however, readily attacked both the non-flashing and flashing lures.

The better eyesight of the big brown bat could be a factor in the difference in response. In addition, the echolocation calls of these three species differ. The echolocation capabilities of the little brown bat and the northern long-eared bat compel them to approach more closely than the big brown bat in order to detect their prey. The big brown bat, with its better eyesight and ability to detect prey from a distance, has time to break off before its attack on a firefly, while this is not true of the other bats.

This study demonstrates that for some bats the mating flash of fireflies is a warning signal of an unpalatable meal, while other bats discover this only after tasting and rejecting the firefly. In either case, fireflies are not part of the diet of these bats.

On one hand, the flash mating signals of fireflies prove a detriment to their survival as it attracts predation by Photuris fireflies. But this risk may be offset by the benefit gained from their flash being a deterrent to predation by bats.

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