Model of Feeding 1 P. pyralis larvae encounters earthworm and injects it with a paralyzing venom.
Observations with respect to the chain of behaviors displayed by Photinid larvae which exhibits repetitive and sequential prey behavior through a prescribed patter of earthworm attack, paralyzation and vivisecting followed by liquefying and devouring the earthworm's heart and body alive; and generally, the profound implications of chained feeding behavior with respect to the nature of instinct.
Observations of Photinid larvae (probably Photinus pyralis larvae) collected 10 Feb. 1974 in Jacksonville, Alabama suggest a sequence, train or chain of probable behavior associated with feeding.
The following related figures and illustrations are from firefly notebooks in which were recorded original observations, rearing chambers, designs and techniques employed or considered:
First observation of Photinid eating earthworm
Photinid vivisections earthworm into three sections
Photinid feeding on vivisected midsection of earthworm
Rearing Photinid larvae in coffee can chambers
Glass chambers and container designs to enhance observation and rearing of Photinid feeding behavior
After making initial observations of how a Photinid larvae attacks, vivisects and devours an earthworm, models were made and this behavior was photographed. I used readily available polyvinyl plastic fishing lures to construct these models and positioned them to represent the probably sequence of behaviors Photinid larvae exhibit when preying upon earthworms. Photographs were made using a Logitech QuickCam. Note that actual photographs of larvae feeding were not made owing to the fact these initial studies were made in 1974 and I was merely trying to create illustrations for the probably behavior observed. I would like to challenge anyone interested in this behavior to collect and photograph living larvae and earthworms to document this actual behavior. Some aspects of this behavior are not shown in the models. For example earthworms may respond to larvae attack by rolling up and as larvae eats the earthworm it is liquefied before being ingested by the larvae. Also the larvae may swell up increasing its body may while feeding.
1. Larvae having emerged from eggs burrow into soil. Note that I have established the fact that Photinid larvae burrow in soil by collecting them from the upper few inches of soil, then observing the larvae to burrow beneath soil inside small observation chambers made for this purpose. Also larvae of Photinus pyralis hatched from eggs are burrowing in nature, their bodies long and slender, perfectly indicative of a burrowing species.
2. Larvae encounters earthworm. This may be at any point along the earthworm's body, including anterior or posterior ends. Do not assume that a larvae with encounter one end or the other of an earthworm. Because an earthworm's long body constitutes a greater area than either end segments, in all probability a firefly is most likely to encounter an earthworm along any part of its body.
3. Larvae gently pricks earthworm, as if kissing the earthworm, while holding securely to substrate with its anal appendage. Larvae may also use its anal appendage to secure itself to prey.
4. Larvae injects earthworm with a venomous neural toxin which causes contraction of muscles as indicated by the fact earthworms preyed upon by larvae maintained in a Petri dish with potter's clay initially respond by rolling up into coiled masses rather than extending themselves to escape larvae.
5. After effectively immobilizing or paralyzing the earthworm, larvae preforms a dual vivisection of the earthworm. This involves chewing the earthworm in half near its heart or midsection, literally digesting the earthworm's segmented body to cut it in half.
Then larvae again cuts earthworm so as to free and separate the midsection of the earthworm so that the earthworm is in three parts (essentially cutting out the earthworm's heart and/or its effective action in pumping of blood). By performing this prescribed dual vivisection, the larvae cuts out the midsection of the earthworm, and effectively paralyzing the earthworm, that neither the anterior or posterior section will have fresh blood or oxygen supply, that the slivered anterior ends of the earthworm may not escape as paralytic agents dilute, oxidize and/or wear off, such that the larvae is assured a complete earthworm feast!
Note that this behavior suggest the larvae may actually sense the earthworm's heart beat and/or muscle contractions, and may use this perception in establishing initial segments upon which to feed to divide the earthworm into sections. Perhaps this may help explain one way in which the sensory hairs upon a Photinid larvae's antennae are used; ie, to detect an earthworm's heart beat or muscle contractions and enable proper sectioning of the earthworm so as to disable its heart action.
6. Larvae generally devours the midsection first, then precedes to ingest the two ends of the earthworm, one after the other.
7. Earthworm is not able to escape as neural toxins have caused the earthworm to lose control of its muscles such that they can not extend, plus the fact its midsection/heart has been but out.
8. Earthworm is devoured alive by the Photinid larvae. This involves injecting digestive enzymes into the earthworm, then ingesting the liquefied earthworm.
9. As the larvae eats it swells up, expanding greatly in mass. After completing its earthworm feast the larvae may moult. Then the larvae may eat another earthworm.
10. The Photinid larvae repeats this process of preying upon earthworms, over and over, as it grows through moulting until the larvae is ready to pupate, usually in early spring and summer for species in North America. An adult firefly emerges, mates and if a female deposits eggs which will hatch in 12-14 days. Then the process begins anew with larvae burrowing into soil and preying upon earthworms.
I. This train or sequence of feeding behavior in Photinid is in keeping with its anatomical structure especially when contrasted with that of the Photurid larvae. The long, thin body of Photinid larvae is indicative of a burrowing larvae rather than one which forages atop leaf litter and debris upon the forest floor. As a burrowing species Photinid has evolved an ingenious set of behaviors all directed at its primary prey, earthworms (which may also include nematodes for very young larvae). By paralyzing and vivisecting its prey Photinid, devouring its heart or midsection, Photinid insures its survival through enabling it to feed upon the entire bio mass of the earthworm.
II. This feeding behavior suggest that Photinid larvae (a) occur only or primarily in soil habitats which support earthworms (b) growing and metabolism of larvae will be at highest rates in soil with temperatures warm enough to permit feeding behavior; ie, the eating of earthworms (c) life span of firefly larvae (period between hatching from eggs and pupation which larvae lives in soil) may be shorter for warmer climates than colder climates, such that in colder climates larvae may take more than twelve months to mature whereas in warm climates larvae may mature in 12 or less months with larvae state being of shortest duration in tropical locals.
III. If larvae in tropical climates grow at an accelerated rate relative to those in colder climates, rearing of tropical species of Photinus would be recommended over species common to temperate climates or more northern latitudes. For example an ideal species to rear might be the Jamaican firefly, Photinus pallens (Fabricius). This is also suggested by the fact this species occurs (has been observed) in adult form for most months of the year and feeds upon the nectar of flowers which may have the effect of maximizing life span of adults and permitting females to deposit a high number of health eggs likely to hatch.
IV. The chain of behaviors associated with Photinid's eating may help explain what causes this species to occur in certain areas and/or disappear from some areas. Because a Photinid larvae can only survive where earthworms occur, it is likely to be found only in those areas which have soil that supports a healthy earthworm population. Should some factor be introduced with disrupts the earthworm population, Photinids are likely to disappear. Also should some factor occur which deprives Photinid of its earthworms before they can be devoured, this will impact the survival of these fireflies. For example, should fire ants steal partially eaten section of earthworms before the Photinid larvae can consume its full meal, this will adversely effect the Photinid's ability to survive. It should not be surprising then, that Photinid's may disappear in some areas ravaged by fire ants.
A successful rearing program for Photinids may incorporate feeding the firefly larvae live earthworms. Given the fact that Photinid larvae (and most probably Photinus pyralis larvae) eats living earthworms and has adapted a special feeding behavior with respect to preying upon earthworms, live earthworms would be the food of choice in rearing Photinid larvae, (especially Photinus pyralis larvae) whether from larvae hatched from eggs or specimens collected from the field. In other words the chain of behavior which Photinid larvae go through with respect to feeding, if broken or impeded at any point by changes in the environment, may adversely effect the survival of the firefly species. In fact the basic concept that insect behavior can be broken down into chains of behavior is a very useful concept with respect to understanding insect behavior and may, if fact, have some genetic basis of programming, such that behavior proceeds through a sequence of steps that is like reading a genetic code or track of patterns which control behavior, this being the method or mechanism by which all heretofore designated "instinctive" behavior has its origins.
This chain of probable behaviors exhibited by Photinid in its preying upon earthworms is a subject for further study among the many species. Some of the questions one may seek to answer through collecting larvae in the field and/or obtaining larvae of known species by hatching them from eggs are:
(1) Do Photinids prey upon nematodes as well as earthworms? I have observed what appear to be nematodes in dead Photuris larvae. Were these nematodes parasitic or infective agents of decay? Did the Photuris larvae ingest nematode eggs which then hatched inside the firefly larvae or did these nematodes come to infect the Photuris larvae after it expired?
(2) Do Photinid larvae, especially large larvae, actually stalk earthworms, perhaps following their scent or slime trail through earthworm burrows? When encountering an earthworm in a burrow does feeding behavior vary from that described above? Do all varieties of Photinid prey upon earthworms in the described fashion or does this feeding behavior vary from one species to another?
(3) What is the chemical nature of the neural toxin or venom used by Photinid larvae? This must be a very toxic agent and it may have applications in medicine. How can this chemical be collected and synthesized? One method of collection would be to actually use a microscopic capillary tube to such the fluid out of a firefly larvae's grooved mandible. Is this chemical the same as that which makes up the white, milky secretion of adult Photinus?
(4) It would be a challenge to video tape Photinid larvae feeding upon live earthworms. It may be possible to do this rather easily by using a low light sensitive video camera, perhaps set on time lapse, with an I.R. strobe. Simply place the larvae and earthworm inside a Petri dish upon moist potter's clay and leave undisturbed while video tapping. If one collects large Photinid larvae in the winter or early spring, they may be starved for a few days or week before attempting to video tape feeding. The larvae will then be hungry and may tend to eat soon after it is offered a live earthworm.
(5) Experiment with earthworms in order to better understand the feeding behavior of Photinid larvae. Slice up living earthworms in a manner similar to that done by firefly larvae. Are the end sections able to heal? If end sections are treated with the milky white exudated substance from adult fireflies, with this paralyze the earthworms in a manner similar to that done by the firefly larvae themselves. This idea here is to try to duplicate how the Photinid larvae feed, perhaps even measuring the nerve or muscle activity of the earthworm. One could then compare this with measurements of nerve and/or muscle activity of earthworms which are actually in the process of being preyed upon.
(6) The matter of how "instinctive" behavior is encoded in genes deserves serious and intensive study. What is the process by which genes or gene encoded behavior is read or translated from a genetic code to an actual sequence or chain of behavior? The fact that insects in general exhibit trains or chains of sequential behavior suggest that some code or pattern is being read or followed. Realizing that trains or chains of behavior occur and describing these is a first step in being able to understand how said behaviors are altered if genes are varied. Learning to rear fireflies and study how their behavior may vary with changes made to their genetic structure may yield significant knowledge with respect to how behavior may be linked to genes from one generation of insect to another.
(7) I would love to see someone make computer models of firefly larvae predation upon earthworms, snails, slugs or other soft bodied animals. This could be done much the same way figures are animated by motion picture studios to produce real live motion in gaming or war simulators videos. Simply make models which have white points to reflect light such that the motion of the models may be digitized. Then once a digital firefly larvae and digital earthworm, snail or slug is inside a computer, the possible motion and interaction of the models may be explored and/or simulations made to illustrate observed behavior. This is the same type of technology used to animate dinosaurs in movies. There is no reason this could not be done with firefly larvae to better gain some insight into their behavior as well as produce some dynamic predation videos for educational purposes.
Why I imagine one might even be able to create some alien space creatures with anal appendages and grooved fangs which would even strike terror into Sigourney Weaver! :-) Jest aside, one should not over look the practical application for computer simulation of insect behavior in general, and larvae behavior in particular, in the making of educational documentary films as well as Hollywood films where a giant firefly larvae may attack New York City and put Godzilla to shame. :-) In fact, movies like George Langelaan's classic "The Fly" starring Vincent Price (I'm referring to both the original 1958 version of this movie and the 1989 remake of The Fly) probably made more money than most entomologist make in a life time! Plus, judging form the number of hits one get on the Internet when searching for relations betwee"Disney" and "ants" there seems to be a big demand these days for anything concerning insects. I have little doubt a stuffed firefly larvae would make someone a millionaire.
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