Recently I collected and hatched a batch of firefly eggs and obtained over 200 tiny firefly larvae. These were placed in one-half pint jars for observation and study. There were several questions that had been plaguing me. For one, I was wondering, "Do these tiny firefly larvae eat only live food, or will they accept dead food?" This was a pressing question for anyone interested in rearing firefly larvae, as if anyone is ever going to be able to rear these little buggers; i.e., P. pyralis, on an artificial diet, than one must know if they will eat dead food.

I also wanted to make a video tape of P. pyralis larvae attacking and eating an earthworm. In the process of trying to answer these and other questions, puzzles which are probably of no concern to anyone else in all the world but me and perhaps a few other entomologist or behaviorists, I chanced to place a live red earthworm in a container of firefly eggs and larvae. As the earthworm crawled about the firefly eggs stuck to its slimy surface like metal to a magnet! The eggs remained stuck to the earthworm despite vigorous twists, turns and gyrations, as the earthworm was being attacked by tiny firefly larvae. It seemed no matter how much the earthworm squirmed it could not detach either the tiny firefly larvae attached to it or the eggs which now became attached to it in greater numbers as to squirmed inside the jar.

This was a remarkable discovery. I'd read most of the world's literature on fireflies, or synopses thereof, and could not recall ever there being any mention of the fact that firefly eggs readily stuck to earthworms. What this meant is that if an earthworm happened to crawl by and brush a firefly egg, the egg would attach itself to the earthworm. Thus wherever the earthworm went, so would go the egg. Then when the firefly larvae would emerge from the egg, it would be able to attack the earthworm and not have to search for its food.

This also brings up a host of other questions. Do female P. pyralis fireflies lay their eggs in the vicinity of earthworms or even upon earthworms. Certainly these fireflies deposit their eggs upon soil, in the upper layer of leaf litter in the habitat where earthworms would be likely to occur. But it would be interesting to learn if the presence of earthworms will result in females of P. pyralis actually depositing eggs upon or near the earthworms.

Also of great interest to me is the manner in which tiny firefly larvae of P. pyralis attack a live earthworm. When a 5 cm long red earthworm was placed in a one-half pint jar which contained some 50 or more tiny firefly larvae, the earthworms was promptly attacked by firefly larvae. Each bite of a tiny firefly larvae resulted in a sharp contraction, the earthworm would jerk, roll, twist and turn to vigorously attempt to dislodge a tiny firefly larvae. But the larvae which had attached itself to the earthworm using an anal appendage covered with thousands of tiny hooks, remained attached despite the earthworm's vigorous efforts to dislodge it.

I made a two hour video of this behavior, a segment of which I hope will one day air on PBS, the Discovery Channel or the National Geographic Channel. But should these networks not view this as headline natural history news, at least I have significantly documented the behavior which I regard as one of the most remarkable examples of aggression in the animal kingdom.

This behavior is analogous to a snake biting and killing a human being or to killer whales attacking and killing a much larger whale. Certainly one can not view the aggressive behavior of firefly larvae and naively continue to view fireflies as a gentle species which brings charm unto a summer night. Firefly larvae are predacious carnivorous which possess highly toxic venom which digests their pray alive! These creatures are not simply harmless organisms which have a tail that lights; they are an aggressive species, which aggregate together like members of a tribe, to hunt and kill their prey and feast upon its flesh. They glow not so much by chance or accident, and certainly not to without purpose; rather, they glow because this serves as a signal to other firefly larvae saying, "There she blows! Moby Dick, the great white whale of an earthworm has been grappled by my anal appendage hooks! Come one, come all to the kill, to the feast!"

This analogy may seem a bit anthropomorphic to those entomologists and strict behaviorists who shun making comparisons to animal and human behavior. But certainly the fact that P. pyralis larvae glow brightly in alarmed, attaches itself to earthworms which struggle violently in response, and aggregate all lead to one simple conclusion: P. pyralis uses its light in hunting earthworms, that tiny larvae may each contribute to the hunting and killing of earthworms, so each contribute, one to the other to the survival of the tribe; that these firefly larvae function not as single individuals, but in small groups or aggregates, that their survival as individuals depends upon the survival of the group or aggregate!

Thus at least in the case of P. pyralis the reason firefly larvae glow is because it signals other firefly larvae that an earthworm has been located, such that firefly larvae use their glow as a form of communication with respect to hunting for their prey which is earthworms. This is a very significant discovery and certainly lays to rest forever the idea that firefly larvae glow for no reason at all. At least in the case of P. pyralis, bioluminescence is of extreme benefit to the survival of the species as it directly relates to firefly larvae being able to find, kill and eat their food.

Once P. pyralis has attacked and immobilized an earthworm the prey is then slowly digested. Larvae will excavate a cavity around the earthworm, bury it and devour the earthworm's flesh over a period of hours or days. Thus what would be a difficult task by a single tiny firefly larvae is enabled by a group or aggregate of firefly larvae. This is the rudiments of social behavior and enable fireflies to survive as a group, aggregate or tribe, where singular individuals would soon perish unable to provide food for themselves.

Indeed, these are remarkable observations and discoveries. They are headline news in the world of fireflies. Ah, but that is a world where only a few dwell, as humans are too concerned with their own sexual behavior and aggressions toward their neighbors and the rest of the world to bother about fireflies. After all, what are these flashes in the night, but pretty dancing lights!

Sincerely,
Terry Lynch
Date: 2 July, 2003

Do you have a beef? Send your comments, opinions, letters or other remarks to Byteland. In doing so, you agree that all submissions may be reprinted, edited and/or published without compensation or restriction whatsoever. Warning: If you send hate mail or other trash we may publish it and you agree to release Byteland.org, its agents and representative, from all liability, whatsoever, and to be totally responsible for your own statements and/or actions, including but not limited to slanderous or libelous remarks! You also agree to release Byteland.org, its agents and representatives, from any claims of slander, libel or other damages whatsoever, in regard to reprint, publication or editorial comments or usage with respect to any material you submit for publication.