by Terry Lynch
1 July 2001
Firefly Mysteries presents revelations related to the rearing, egg, embryo, early instar and behavior of Photinus pyralis larvae with respect to gregarious feeding behavior, vivisection of host food via digestive enzymes, interring of earthworms and proof larvae use eyes and lanterns to form aggregates. This report is a challenge for investigators with emphasis on the role firefly larvae may play in research into the genetic key codes which link and differentiate flash pattern to species.
Fireflies exhibit a number of mysterious behaviors beyond their mere flashing. Although recent reports give insight into how fireflies flash, there remains many unanswered questions related to fireflies and their behavior.
Having studied fireflies for over 30 years their complex behavior continues to amaze me. Most people fail to realize that there are hundreds of species of fireflies and that fireflies live the majority of their life as larvae, unseen and hidden from the casual observer who is dazzled by the summer time courtship flight of short lived adults.
What makes one genus-species of firefly differ from another is perhaps the greatest mystery of firefly behavior. It has been established that adult fireflies use complex signaling pattern in their courtship but the nature of these complex flash patters, though described for a number of species, remains mysterious. In fact we hardly understand what makes one genius of fireflies differ from another, much less how the numerous species encode and modulate their distinctive flash patterns.
Study of firefly larvae emphasizes that the difference between the various genus of fireflies includes extreme variations in morphology at the larva stage. Although differences in genus of fireflies carries over to the adult forms, morphological differences between the various species often becomes vague. One firefly species may so resembles another that only their flash patterns can distinguish two different species (See James E. Lloyd's work in describing the flash patterns of a number of species of fireflies).
As structure is linked to genetic code, the key to each firefly's organization and presentation of structure may be viewed as an unknown code. The nature of this code from species to species also holds the key to why each species flashes with a unique pattern used in its courtship behavior. Identifying and reading this code remains one of the greatest mysteries related to firefly behavior.
The study of firefly larvae presents an opportunity to explore in greater depth the factors which cause differentiation of genus and species. This is because all the genetic information expressed in adult fireflies is contained in the larvae. Although we may not yet know how to read or decipher that information it is still locked in the genetic code of firefly larvae.
One of the problems then, is obtaining firefly of known genus and species for research; i.e., of known parentage. The methodology for securing I-instar firefly larvae has basically been worked out. One of the significant results which should follow is that a number of larvae from known parentage may be secured for genetic analysis. By making comparative genetic analysis of larvae from say P. pyralis
and Photuris sp. one may begin to decipher the differences in genetic code which characterize how the genus vary apart from variations in individuals. Applying these same methods to several varieties of Photinid will begin to reveal genetic code variations between species. Hence working with firefly larvae, rather than adults, may prove very fruitful.
Figure 2 above illustrates a simple egg collection chamber for obtaining I-instar P. pyralis larvae. Adult females of the species may be located in the field by using a pen light to pan the search area. When one mimics the flash of males (panning an area each 5-6 seconds to produce a short flash), females perched on the ground or vegetation will respond in approximately 2 seconds. I've used this method repeatedly to collect numerous female P. pyralis, generally occurring in the early summer (June-July) in central Alabama. Then it simply is a matter of placing the females in a jar with males to permit copulation. Once a female copulates, which may last 2-4 hours, they are set in egg collection chambers where they deposit eggs.
Females are maintained in egg collection chambers with males and allowed to copulate with males each evening or as may occur. The females then deposit their eggs over a course of days. Just before larvae are ready to hatch from the eggs, sharp vibrations will cause the larvae inside the eggs to glow brightly. After about 14 days young I-instar larvae will begin to emerge and may be collected for study.
If you are interested in the rearing of fireflies and/or behavior of early instar firefly special galleries have been provided for your review. To see developing eggs which have been photographed under a variety of lighting conditions please visit the Egg and Embryo Gallery. Behavior of early instar larvae is illustrated and recorded through a series of dymanic photographs in the Firefly Larvae Gallery.
The above described procedure for collection of P. pyralis eggs and larvae also works to collect I-instar larvae from Photuris sp. However the collection of adult Photuris usually involves scooping them out of the air as they flash or locating the blinking females flashing upon the ground. Both the male and female of Photuris readily fly and may be netted. The females of Photuris are easily distinguished from the males by their pointed posterior abdominal segment and ovipositor. Another interesting behavior of Photuris is that the female will attract males of P. pyralis by mimicking the flash response of a female P. pyralis. Then the female Photuris will devour the male of P. pyralis, eating them alive! This aggressive mimicry was first described by James E. Lloyd. Photuris females will also eat male Photuris which may enhance the egg laying of female Photuris, given a well fed female has the nutrition required for good egg laying. Also Photuris females readily lay eggs when placed in jars of sand or soil and the emerging larvae seem to be scavengers, so may be more easily reared than P. pyralis, which may be host specific.
Figure 4 shows a typical firefly orgy. Generally when a female P. pyralis is placed in a mating chamber with more than one male, there is competition for the female. In the field this behavior may also be observed and involves several males attempting to recognize the female and copulate. Yet males will continue to attempt copulation, probably aroused by pheromones. In fact anyone who has spent much time collecting quantities of P. pyralis can tell you these fireflies have a distinctive bitter taste and rather poignant odor. These pheromones have been reported to have a protective role as small animals do not like the taste of fireflies and will often refuse to eat P. pyralis. Also the female pheromones seem to drive the males nuts! Males become so aroused by the female that they even try to copulate with other males -- or at least this is the impression one gets. Actually males all are trying to copulate with the female and they poke and probe with their posterior genitalia seeking a union even after a female has already copulated with another male. I've little doubt this behavior may have contribute to both the length of a male firefly's body and penis, that long protruding hairy hook which males extend around and about other males when vying for a female's attention.
Figure 5 illustrates a pair of P. pyralis resting while copulating. Copulation generally lasts for 2-4 hours. The female being somewhat larger than the male will drag the male around to find a new perch should this be required. Walking up stems or leaves the copulated female may escape the attention of other males. Once copulated a pair remains oblivious to what's going on around them. The attentions of other males are ignored. One may tap or knock upon a jar containing a copulating pair and these vibrations do not seem to bother the pair. They may even be gently moved or handled upon a small twig, stick or straw, as when transferring from one container to another, without disturbing the copulation. However if handled too roughly, especially in the wild, the female may become catatonic and/or fall from her perch. By "too rough" I mean trying to pick up the copulating fireflies or to hold or grasp them. Such rough behavior may signal a defensive response, such that the female tries to drop or fall and escape or in the case of a female that has completed copulation, she may actually become catatonic.
After copulation the female may rest or if handled too roughly she may become catatonic, feigning death. This catatonic state is apparent when the antennae become limp! Apparently the blood in the antennae is sucked out so that the antennae become loose and flimsy, without any rigidity. A catatonic female will remain motionless for many minutes before rigidity is restored to her antennae by pumping blood back into them. Generally I have observed this behavior only when handling a female too roughly.
Obviously this catatonic behavior so evident in a female which has just copulated and is handled is extremely beneficial to the survival of the species. A female which has copulated carries both sperm and eggs and her sole mission in life is now to fertilize and deposit those eggs. Toward this end the female will become catatonic and feign death if disturbed too roughly, which probably protects the female from spiders or other predators. This behavior also explains why a female will loosen its grip on a leaf or twig in the field when one is collecting them. By becoming catatonic a female will fall to the ground and escape capture by large rough handling predators or people trying to collect them. This has been my experience in collecting females such that the method I use is to let the female drop into a net, jar or other collection vessel. Generally females may first try to escape, burrowing to hide in leaf litter; but if the male and female become separated and one picks up the female, squeezing or holding it, then when set down she may feigne death for many minutes.
Egg laying is a process which occurs over a period of days. Having copulated a female will deposit her eggs in the soil, probing with her ovipositor into the most minute of cracks and crevices. These soft eggs soon harden into tiny pearls which glow! In fact over a period of some 14 days as the larvae inside the eggs mature, the eggs will become responsive to vibration and glow very brightly when a sharp vibration occurs in their vicinity. This may be observed by setting a Petri dish of firefly eggs on a a table or counter top in a completely darkened room. Then after letting one's eyes become accustomed to the darkness, tap the Petri dish. The larvae inside the eggs will glow brightly. This is best observed a day or two before the larvae emerge form the eggs.
I first observed this firefly egg glow due to vibrations in 1968. After collecting numerous eggs, putting them in a Petri dish with moist tissue and letting these rest undisturbed, they were observed daily. Several days before the larvae emerged the eggs were observed in complete darkness. A light tapping upon the Petri dish caused a bright glow which then faded. This indicates that larvae inside the eggs have matured to the point of being able to take in oxygen and flash their lanterns when their nervous system detects vibrations.
When firefly larvae emerge from eggs they are white, not having yet taken upon a darker coloration. Photomicrography of such tiny larvae enables one to easily see the internal structure of larvae without need for intrusive dissection. Simply place the colorless, transparent larvae upon a microscope slide in a drop of water, lay a cover slip over the larvae and observe it under various powers of magnification. Using this method one may explore the various morphological variations between the genus-species of various fireflies in their larvae stages. These young larvae should also be an invaluable resource to genetic researchers searching for the code keys linking flash behavior to genes, for firefly larvae of common parentage and of known genus-species are the only source of genetic material that is identical, from individual larvae to larvae, such that this enables repetitive comparative analysis of DNA.
Although I have not been fortunate enough to enjoy access to a well equipped laboratory or the resources to support an in depth, expensive investigation into the nature of firefly flash key codes, by which I mean those genetic chains of DNA which describe the flash patterns which link and differentiate species, it is clear firefly larvae research might yield a wealth of information in this respect. Some of the questions which may be answered are:
If the study of firefly larvae may help answer these fundamental questions, certainly more time, effort and resources should be devoted to this topic. As an amateur naturalist and firefly researcher working out of my suburban laboratory (See Figure 5) I've made a number of significant first time observations and discoveries. These include:
Figure 6. Suburban entomologist in Desert Storm camouflage writing firefly journals with microscope, red insect net, specimen bottles, paraphernalia and inquiring mind, everything needed to explore the back yard jungles of American suburbia.
I've often wondered what other discoveries I might be able to make had I the time and resources to devote my full attention to the study of entomology and animal behavior? Should any university wish to offer me an honorary doctorate and position to pursue such research, I would certainly consider this a well earned opportunity. Also I will accept donations and grants to support my firefly and entomological research. In fact, I'd like to build a natural history museum and science research center one of these days. If you would like to contribute toward this effort you may make a donation via PayPal. Simply click on the PayPal button below, set up your account and then make your secure payment using your credit card or a bank transfer. Thank you.
In addition I will accept any gifts of laboratory equipment or supplies including computers, photographic equipment, microscopes and reagents. People who would like to contribute firefly specimens should contact Terry Lynch. I am in special need of living female fireflies from around the United States. I would also like to obtain living aquatic males and females from the orient. In addition I would like to obtain any books or reference materials related to entomology which anyone may have which they would like to discard. I'm especially interested in a first edition of the 10-volume Souvenirs Entomologiques by Jean Henri Fabre, English translations of Fabre's work and back issues of Scientific American, especially those with articles on insects and/or bioluminescence.
It should be seen from these considerations that fireflies remain some of the most mysterious and wondrous of insects. Much remains to be learned about them. Recently it was discovered that the flash of Photuris sp. is triggered by the release of nitric oxide when a signal is sent from the firefly's brain to its lantern. Yet we still don't have much of a clue to what goes on inside the brain of a firefly. Nor do we know how that tiny little firefly mind controls its flash patters and how this is linked to code keys in strands of DNA. Clearly there could not be a more compelling area of research for teams of eager scientists with the systems and resources, plus the brain power, to attack these problems. Should this come to pass in my lifetime, I might gladly contribute some effort to providing a few P. pyralis firefly larvae.
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The following firefly presentations by Lynch may also be of interest:
Project K9 | Blinks and Links | The Urban Jungle | Firefly FAQs | The Amateur Naturalist | Firefly Notebooks | Feeding behavior of Photinid larvae | Flash Keys in Fireflies | Contact the author
Home | Introduction | Firefly FAQs | Blinks and Links | Eggs and embryo | Early Instar | Firefly Art | Evolution | Flash Keys in Fireflies | Firefly Notebooks | Photuris | Contact the author