Hunting Bats, Fireflies and Bioluminescence

"[These ferocious hunters -- little brown bats -- exert  incredible selective pressure on their prey [consuming their body weight insects nightly]."
"These bats are from the western United States, where there are essentially no fireflies [big brown bats introduced to eastern fireflies]."
"[The large brown bats rejected the taste of fireflies; never have I] seen a stronger negative reaction [to a chemically defensive insect. The bats] salivate a bunch and they cough and shake their head and just generally completely despise us [researchers] for giving them that prey."
"This is, to my knowledge, the first work to show that a three-dimensional flight pattern is information that bats can associate with bad taste."
"Getting a natural predator and its prey to interact in a way where components of the warning signal can be isolated and dissected is inherently challenging and requires novel methods and experimental design. In fact, this study took us two years to refine methods and two additional years of data collection."
Jesse M. Barber, biologist, Boise State University

Fireflies are often toxic to bats, which see the nighttime flashing and steer clear of the insects, according to a new study.  Paul Moosman Jr.

"I had found a new species [of firefly] and was trying to catch as many as I could in my net [so held a few in his lips and mouth preparing an enclosure]."
"As it was, my throat started constricting and my lips went numb [reacting to the bitter, acidic taste from holding the beetles in his mouth careful not to crush them]."
"With all of the data that is currently available it certainly appears as though the first bioluminescent fireflies first arose around the same time as bats."
Marc A. Branham, biologist, University of Florida, study co-author

Fireflies repel bat attacks with bioluminescence and slow, predictable flight. | Stephen Marshall

"[The study presents] convincing evidence that bats of this particular species learned to avoid fireflies more quickly when they received information through two different sensory channels."
"Flying plus bioluminescence was the magic combination that really enhanced bats' avoidance learning."
Sara M. Lewis, biologist, Tufts University

"Any discussion on how bats may have impacted the evolution of firefly bioluminescence is pure speculation and certainly does not apply to larval bioluminescence, which defines fireflies."
Kathrin F. Stanger-Hall, firefly expert, University of Georgia

There we are again, a new 'breakthrough' study convincing its authors they have discovered the natural revulsion of a carnivorous species to the natural chemical protection of a prey species through diligent research led by intuition, building on a previous century's observation by an earlier biologist reaching his conclusion by observation alone. The carefully constructed study leading to the conclusion by the researchers involved that fireflies' famous bioluminescence goes beyond a courting ritual to represent a warning to predators that they needn't bother hunting them because they taste awful, has other experts in the field both approving and denigrating the conclusion.

The sight at night of tiny winged creatures lighting up their presence couldn't be more charming; a sight that parents enjoy exposing their children to, for the fairyland-like atmosphere it evokes and the wonder it brings to children's imagination. Well, scientists too have wondered about why it is that fireflies light up as they do in the dark. In the late 19th Century entomologist George H. Bowles theorized: "May not the light then serve ... as a warning of their offensiveness to creatures that would devour them?"

That inspired hint to the purpose of the fireflies' bioluminescence was taken up over a century later by two present-day biologists, Drs. Barber and Branham and their colleagues. That fireflies communicate through the light they emit has been known; that there is a firefly 'language' in blinks that 'speak' to other fireflies. But it was the intriguing thought that another function attributable to the light exists, one that served to prolong the lives of fireflies, that motivated the study and led to its conclusions, more or less verifying the brilliant guesswork of 19th Century Dr. Bowles.

A study published in the journal Science Advances had the research team introduce common eastern fireflies to a group of big brown bats, unfamiliar with fireflies in their geographic region. In the region of the U.S. where the big brown bats live, fireflies don't produce bioluminescence. Both bats and fireflies were placed in a dark chamber for between one to four days. The bats snatched fireflies on day one, reacting swiftly by rejecting the firefly, once tasted. High-speed video cameras set up in the chamber showed bats eating scarab beetles and moths, and rejecting the fireflies.

The beetles' toxic taste was quite obviously not to the bats' taste; once introduced to the bitter flavour of the fireflies the bats never again attempted to catch and eat the fireflies. The blinking lights were associated with a disgusting meal evidently; the intuited purpose of the lights. And it was not only visual identification through blinking lights that led the bats to understand the fireflies did not represent a tasty meal. Researchers took to brushing red or black paint directly on the beetles' abdomens to block out the light.

The warning lights now absent, the brown bats reacted once again by catching the fireflies, then immediately spitting them back out in reaction to their nasty taste. In response to this new challenge, the predators began to recognize the flight patterns of the light-darkened beetles, the result of which, once again forewarned, the bats rejected the beetles as prey. Echolocation to sense the wing beats of the fireflies was used by the bats to recognize the characteristic lazy flight patterns of the fireflies.

The "nonchalance of a chemically protected insect", observed Dr. Barber, comparing it to the leisurely waddle of a porcupine, an animal endowed with a natural potential threat to would-be predators, complacent in the knowledge that other animals will give it wide berth or risk being uncomfortably skin-penetrated by the porcupines' long barbs.