Figure Z. With its anal appendage firmly attached to a glass microscope slide, a Photinus pyralis larva rips out a fiber from an earthworm section, pulling and tugging ferociously! Debris in background is condensation on outside of polyform cell which had been set in a moisture chamber prior to taking this photograph. Observing the larva's mandibles firmly gripping earthworm tissue affirms the feeding behavior of early instar P. pyralis larvae as being a preference for earthworms. The fact that even very tiny larvae can tear apart tissue from much bigger earthworms suggests that small larvae may be able to attack earthworms which are much larger than themselves, secure their meal by tearing off fiber and tissue, then escaping with the booty to feast in peace. I had long wondered how tiny larvae might feed upon earthworms which might be too large for them to paralyze and eat entirely; this observation suggest that tiny larvae may eat small portions of larger earthworms, ripping tissue out from the inside of earthworms. The earthworms could then crawl away, perhaps regenerating their lost tissue, only to be stalked and attacked by P. pyralis another day.
Figure Z1. 2-instar P. pyralis larvae L measuring 5.0 mm to 6.0 mm in length are shown here some 85 hours after their first feeding. Offered a new section of earthworm E the larvae have again begun to feed. At the middle of the earthworm section, digestive enzymes have begun to contract and divide the earthworm causing a vivisection V. An occasional contraction or wiggling of the earthworm section indicated that it is still alive while the young P. pyralis larvae gorge themselves. At this rate larvae of P. pyralis will probably mature within one year. Photo by Terry Lynch.
Figure Z2. Early instar P. pyralis larvae L do not seem to be bothered by the fact they are being observed and photographed under bright light. They continue to feed without pause or interruption. Such behavior for a nocturnal creature indicates a strong, over powering attraction to the most succulent earthworm E which is its prey. In this respect P. pyralis larvae seem to share with other insect larvae an insatiable apatite for their preferred food. Learning what chemicals play a role in the identification of earthworm by P. pyralis larvae is a topic for future investigation as is the chemical nature of their powerful paralyzing digestive enzyme. Photo by Terry Lynch.
Figure Z3. After 13 hours from introduction of new section of earthworm, a group of larvae L had cut this section of earthworm E in half and were engaged in burying one-half of the section of earthworm. This appeared to be a collective effort or cooperative behavior, as the larvae were not in competition for food; but rather, working together to vivisection the earthworm and bury it. This permits the earthworm to be consumed by the larvae over time and may be advantageous as the earthworm is then protected from other scavengers. This cooperative effort by P. pyralis larvae clearly represents what may perhaps be considered the beginning of social behavior in this species of insect! The fact that P. pyralis larvae may work together to digestively vivisect an earthworm section and inter it is quite a remarkable behavior not previously reported in the scientific literature. Although this observation was made in vitro, it suggest that in nature P. pyralis larvae may exhibit this and other early forms of social behavior. Perhaps their lanterns serve to identify themselves to each other that they may congregate and work cooperatively to secure, section and bury prey, which is a task made easier by a small group of larvae working together, rather than each individual larvae competing for its own food. This is in keeping with the behavior of adult female P. pyralis to be reclusive and not fly, tending to lay eggs in close proximity. Young larvae may then have a better change to locate each other and congregate to work cooperatively in securing, vivisecting via digestive enzymes and interring earthworms. In contrast early instars of Photuris larvae which I have reared appear to be competitive, demonstrated by the fact that they chase one another away from food. Female Photuris also readily fly such that they may not tend to lay all their eggs in close proximity over the period of their short adult life. This would tend to make Photuris larvae less likely to congregate and be able to develop the social behavior observed in P. pyralis larvae. It is highly probably that the group cooperative feeding behavior characteristic of P. pyralis larvae is general for other Photinids and will be found now that observers know to look for this behavior. Photo by Terry Lynch.
Figure Z4. Twenty-three (23) hours after presenting earthworm to P. pyralis larvae they are busy interring their prey. Just as P. pyralis larvae walk by anchoring their anal appendage, crawling with their legs to extend their body forward, then moving their anal appendage forward to make a "step," so larvae L inter their vivisected prey, an earthworm E, by anchoring their anal appendage, crawling or scraping with their legs to move soil particles, sand grains and debris S; thus, cooperatively excavating a small recess underneath the earthworm into which it falls to be covered with soil by larvae diligently and methodically working as a group to inter the earthworm. The fact larvae do not exhibit aggression toward each other and instead work together at the common task of vivisection and interring an earthworm, defines and demonstrates this behavior as being cooperative, resulting in the securement of a large quantity of of food which may be shared by the group of larvae, thus contributing to the survival of the group, a fundamental requirement of any social behavior! Photo by Terry Lynch.
Figure Z5. Approximately 14 hours after presenting P. pyralis larvae L with a new 2.5 cm. section of earthworm, larvae were engaged in attacking the earthworm which was jerking, squirming and convulsing with each apparent bite from the larvae. One larvae was observed to crawl back down into the hole or lair IE where a previously offered section of earthworm had been interred. Apparently larvae come out of their lair at night to hunt, attack their prey and eat, then return to their lair which has been made by the group upon an earlier feeding occasion. Should this behavior which was observed in vitro also occur in vivo, it would indicate that early instar P. pyralis larvae are acting like a social aggregate, tending to live as a group, gregariously, rather than as solitary individuals. Though larger larvae may survive well upon their own, there are clear advantages to gregarious behavior for smaller larvae. They may paralyze and vivisect larger earthworms; they may inter the earthworms along with themselves in a tiny chamber or lair; they may emerge from their lair to hunt; they may defend the lair with some larvae always present to guard their food; and as a group they may continue to secure prey more easily than as single larvae. Their lanterns which glow very brightly green would perhaps aid them in these gregarious behaviors, enabling them to remain in close proximity or even signal a bright flash when alarmed or involved in an attack with a thrashing, squirming earthworm. Also numerous larvae interred with an earthworm section would provide all that many more venomous pairs of mandibles and alarm glows to protect and secure the lair which itself was built by the group through excreting moisture to the soil acquired from the earthworm during feeding, then loosening the compacted soil through a group effort to build the lair. When one combines these gregarious behaviors of the larvae with the fact P. pyralis adults participate in flash recognition communication and orgies, it becomes increasingly evident that this collective behavior is the expression of a community of fireflies which tend to aggregate and be gregarious for the survival benefit this imparts to the group. The manner in which these gregarious behaviors may be genetically linked in P. pyralis, vs. how aggressive, nongregarious behavior seen in both larvae and adult of Photuris is genetically linked, is a matter certainly worthy of future investigation. Photo by Terry Lynch.
Figure Z6. P. pyralis larvae L clustering together approximately 34 hours after having been given a 2.5 cm. section of earthworm E. Larvae had taken up residence beneath the Lincoln head penny which was left in their rearing chamber to provide scale for photographs. When the penny was moved over, this photo was taken to reveal an aggregated of larvae beneath the penny. Apparently larvae are opportunistic, taking shelter under any object they find conveniently located in close proximity to their food source. Feeding lairs are therefore temporary structures and larvae will cluster in close quarters excavating a retreat even under a Lincoln penny! Larvae appear to have been feeding from tubular tissue pulled out of the earthworm, running like a drinking hose from the earthworm under the penny where larvae were congregated! Upon closer observation when the earthworm was rolled over at 36.5 hours into the feeding session, it was revealed that the earthworm's internal organs were totally exposed, permitting larvae to feed upon internal organs. The larvae's collective feeding action's had essentially opened a long section underneath the earthworm permitting larvae to feast upon the earthworms vital organs. Ten larvae were counted but the rearing chamber contains more than this number as 1-instar larvae were observed among those which are somewhat larger. When the Lincoln penny was moved, larvae appeared disturbed, crawling and walking about from their loose-knit cluster. Larvae have been previously observed to glow brightly when suddenly uncovered, so moving their roof top to reveal their sanctuary in utter darkness is an observation worth making in the future. The old section OS of digested and dried earthworm no longer seems to be of interest to the primary aggregate of larvae shown here; yet, there may be larvae still feeding upon the section of earthworm earlier interred. Photo by Terry Lynch.
Figure Z7. At 36.5 hours into the feeding session, P. pyralis larvae have retired to their lair under the Lincoln penny. Earthworm section E was inspected to discover it had been partially digested upon the underside by the collective and cooperative feeding action of larvae revealing muscles, body fluid and entrails T. Acid like corrosion on penny A was imparted when earthworm being attacked by larvae made contact, depositing a bit of soil and slime, perhaps containing venomous larvae saliva, onto the coin. This suggest that larvae saliva is highly acidic and corrosive which is why it so readily liquifies the earthworm. It is doubtful a single early instar larva could so thoroughly slice open a large section of earthworm, yet together larvae may work to paralyze and secure prey much larger than themselves turning pieces of earthworm many times the size and bulk of a 6 mm. larva into a mass of slimy juice, partially digested muscles and internal organs ripped from the inside of the earthworm that larvae may drink of its blood and body fluids like tiny fanged vampires of the underworld! This description is surly to get the dander up of those respected and acclaimed entomologists who profess that all insects should be praised and revered without a degree of anthropomorphism, especially when to do so might jeopardize their positions, result in loss of grant monies and refusal of scientific journals to publish their work. Yet what could be more vampire like than a tiny creature which glows, spits acid (highly digestive enzymes) and wipes its head with its ass (anal appendage) to cleans the debris of its feast from its jaws, then inters itself with its prey to drink every bit of life out of its victim, eventually metamorphosing into a winged creature of the night which hypnotizes young and old alike with its light! That wonder of the summer nights which so fascinates every child as it flits and flutters and flashes in search of a mate, is an earthworm killer, a sleuth of slugs and snails, which eats its prey alive, dining in the soft green glow of its fellows, its true nature hidden from all but the most prying of eyes and minds! Photo by Terry Lynch.
Figure Z8. In the early hours of the morning (01:43hrs. 7 Aug. 2001) a mirror was used to view P. pyralis larvae L busy at work beneath a 1.5 cm. section of earthworm's head E offered 24 hours earlier. This virtual image of the earthworm VE reveals larvae feeding upon and interring the earthworm by gradually creating a recess in the soil beneath the earthworm. This behavior is one which appears to be cooperative, as P. pyralis larvae do not exhibit aggression toward one another as do Photuris larvae. Rather, P. pyralis larvae are gregarious, showing the same hideaways, retreats, or lairs, gorging themselves upon earthworms sections which they laboriously work into the soil, a relentless effort which, when shared by a group of larvae, divides the time and energy required by this task among each participant larvae. This gregarious behavior and interring of prey is probably wide spread among all Photinids and is, in fact, likely to be one of the behaviors characteristic of the genus. Immediately after taking this photo the penny used for scale was moved for a second time to reveal at least nine larvae clustered in a loose aggregate. Photo by Terry Lynch.
Figure Z9. Moving the Lincoln penny which has been used to establish scale in photographs shows a loose aggregate AL of P. pyralis larvae. At least six larvae are clustered in contact with one another while three more are further apart. Two other larvae were feeding upon the earthworm E as was shown in Figure Z8. This aggregate of larvae was also observed in a darkened room after taking this photograph and replacing a 2 cm square of plastic over the larvae so they could be viewed. When a very gentle current of air was produced by blowing into the rearing chamber, larvae increased the brightness of their glow revealing a cluster of small greenish lanterns. Given the gregarious behavior of P. pyralis larvae, it is probable they use their lanterns along with tactile stimuli to form and maintain aggregations. Photo by Terry Lynch.
Figure Z10. That P. pyralis larvae L use their eyes and the glow of their own lanterns to cluster and form loose aggregates is suggested by the fact that when they are blinded by light, they can not maintain aggregation. When a small 2 cm. square piece of plastic was placed over the aggregate which larvae had formed under the Lincoln penny, such that they could be better observed, 22 hours later the larvae were randomly dispersed under the plastic square. This suggest that the light penetrating into the larvae's retreat is sufficient to blind them, such that they can not distinguish the glow of other lanterns. This simple experiment therefore tends to prove that early instar P. pyralis larvae do indeed use both their simple eyes and their lanterns to aid in the formation of clusters or aggregates! Therefore the larvae lanterns are not without function, as previously conjectured, but play a vital role in enabling larvae to locate one another, form close clusters and remain in loose aggregates and associations. This ability to use their eyes and lanterns to form aggregates plays a key role in their survival as larvae which cluster together are able to share labor, divide the energy required to perform task as in interring an earthworm E and combine their resources, as the saliva which paralyzes, dissolves and kills their earthworm prey. Therefore through this simple experiment it is proven that larvae have behavior more complex than previously may have been realized. The larvae of P. pyralis are not solitary individuals, but a gregarious species which uses its lantern and its eyes to establish and maintain a loose association for the survival benefit that brings each individual, the group and ultimately the species. Photo by Terry Lynch.
Figure Z11. Rearing chamber was set in complete darkness by tightly wrapping with aluminum foil to block out all light. After 16.5 hours (at 16:07 hours 8 Aug. 2001) P. pyralis larvae L were observed and photographed. Larvae were found to be tending toward formation of a new loose aggregate AL, with the head of each larvae pointed toward the lantern of another larvae, forming a train or follow-the-leader type aggregate. Two larvae had wondered out from under the cover slip and are not shown in this photograph. One of these larvae was stuck in fungus that had started growing upon the earthworm section. Although condensation beneath the cover slip appears to fog and glare the image, close naked eye observation with a magnifying glass made it apparent that the majority of larvae were now in close contact and tending toward aggregation. This, then, rules out all other variables between the Lincoln penny and the plastic cover slip (nature of materials, surface texture, surface area, capacity to store heat and opacity). The only remaining variable in this controlled experiment is absence or presence of light. This simple experiment will be easy for others to repeat observing larvae under a glass or plastic cover slip when exposed to light or kept in absolute darkness, that it may be easily verified P. pyralis larvae use their eyes to detect lantern glow and form aggregates. This simple, yet elegant and effective, experiment may also be repeated with other species of firefly larvae or other luminous animals which have eyes or light sensitive organs and tend to aggregate. Thus is provided a manner to prove that lanterns are used to enable aggregation via perception of lantern glow in the absence of all other light sources. As this experiment proves P. pyralis larvae use their lantern and sight to enable aggregation, I will refer to this test as Lynch's Lantern Function Test or Lynch's Luminous Organ Function Test in the future and ask others who repeat this experiment with fireflies or other bioluminescent species to use this nomenclature for the test which I devised. This may include attempts to measure the degree of aggregation as by determining the number of aggregates, number of individuals in each aggregate and/or density or degree of aggregation. Photo by Terry Lynch.
Figure Z12. Although early instar P. pyralis larvae may use their lanterns and sight perception of lantern glow to form aggregates in vitro, this certainly is not the only sense which plays a role in aggregation behavior. This is clearly indicated by taking a larvae which has newly emerged from its egg and tanned, then placing it in the rearing chamber of larger, older larvae which have established an aggregate under a cover slip. When this experiment was done and observed under bright light, in effect blinding the newly emerged larvae, said larvae appeared to walk around at random, tapping its head from side to side like a blind man with a cane. The larvae positioned at the "Start" walked in an path around the cover slip finally approaching and crawling under the cover slip. When the newly arrived larvae encountered an aggregate of larger larvae at A, neither seemed to respond (if a glow response occurred it would not have been visible under light). In fact the new, smaller larvae walked around some minutes beneath the cover slip encountering individual and close groups of larvae at B, C, D and then at A again. Finally the young, active larvae discovered the fresh section of earthworm at the "Finish" point. This foraging behavior indicates that the newly hatched larvae was actively searching for food and was able to locate other larvae using its olfactory (taste and/or smell) and tactile senses. But the active larvae did not halt and end its foraging when it encountered other larvae; rather, it continued to walk about until it found the earthworm.
This observation suggest that after larvae hatch from eggs and tan they begin to immediately search for food. If a larvae does not find food quickly it will expire, an occurrence I have witnessed time and again in my efforts to learn to rear P. pyralis larvae. The fact that a newly emerged larvae may locate an established aggregate of larvae and share its food, increases the survival ability of the individual and all aggregate members. If in vivo early instar larvae aggregate and share food this certainly will benefit newly emerging larvae. This would also be the case if P. pyralis larvae generations over lap, such that newly emerged larvae could share the food of late instar larvae which are much more able to catch and kill large earthworms than are tiny larvae. However, I have not observed such behavior in the field, and it may be precluded by the short period of time in some areas in which P. pyralis is active and emerging from pupation.
The behavior of early instar P. pyralis larvae tends to indicate that the larvae use all their senses in respect to foraging and aggregation. Larvae may find other larvae in bright light, as when blinded by sunlight, using senses other than sight. If larvae depend upon being able to see and recognize glow of other larvae in order to produce a tight aggregate, then when observed under bright light, tight aggregates would not tend to form. In contrast, when maintained in darkness larvae would be able to see each other's glow, and tend to form close aggregates. However, larvae exposed to light can still use their olfactory and tactile senses to locate other larvae and food. As larvae are nocturnal they would generally be active at night and able to see the glow of other larvae lanterns, that this perception would naturally aid in aggregation. I suspect larvae may also be able to sense their own discharge and, in effect, be able to mark their territory, as it seems a larvae newly introduced to an aggregate, remains in close proximity to the aggregate, searching for food. This could be just a tactile response, that the newly arrived larva tends to remain under the cover slip as it provides a narrow crevice or niche, but it could also indicate that once an aggregate is located by a new, hungry arrival, it searches within the area of the aggregate for food. For larvae new to an aggregate to actually be able to see the glow of other larvae, this glow perception may act as a stimulus to confirm that the newly arrived larvae has located other larvae. But there may be tactile and olfactory senses also indicating this to the larvae. Larvae, using all their senses, would then tend to remain closely associated to share food and other tasks, such as excavating a retreat or lair. If these observed in vitro behaviors are the case in vivo, then the naturalist may wish to hunt for larvae under logs, stones, pine tree bark, and anywhere larvae may be likely to aggregate. Also these observations reveal a depth, complexity and flexibility of larvae behavior reflective of its total body structure and sensory systems, such that P. pyralis may be viewed not merely as a simple "glow worm" but as an active, aggregating, gregarious species clearly in competition with other genera to dominate the cryptosphere. Photo by Terry Lynch.
Figure Z13. In the early hours of the morning (03:14hrs 10 August 2001) approximately 26 hours after placing a new section of earthworm E in rearing chamber, P. pyralis larvae were observed to be engaged in various activities. L1 and L2 were in aggregate closely clustered under the cover slip. L3 and L4 were under cover slip, not clustered. L5 and L6 had crawled out from under cover slip. L7 was feeding and/or stuck in slim upon earthworm. L8 and L9 were cringed up in white cuticle skins, perhaps moulting. Another larvae L10 (not shown) was foraging outside the field of view. There was a recess R dug out from beneath the earthworm indicating that a number of larvae had probably been feeding, excreting waste and burrowing. Two unhatched eggs are also marked indicating that larvae are still hatching in the rearing chamber.
This observation demonstrates that P. pyralis larvae are active at night and participate or exhibit a variety of behavior. This includes foraging or dispersal, feeding, burrowing, aggregation and moulting. Each larvae is apparently going through a cycle or train of behaviors. This series of behaviors appears to follow this sequence: (1) larva hatches from egg, (2) larva tans, (3) larva forages for food, (4) larva locates aggregate of larvae and/or food, (5) larva feeds, excretes waste, burrows, digs or inters food, (6) larva aggregates, rests (this may be a sleep and growth stage), (7) larvae disperses, forages and moults. After moulting larva begins the sequence of behaviors again. This sequence of behaviors is repeated over and over until larvae are ready to pupate and metamorphoses into adult fireflies. Therefore as time progresses and a range of age of larvae occurs in the rearing chamber, it should not be uncommon to observe and photograph individual larvae engaged in various activities at different hours of the day or night. Of course aggregation may be more apparent during daylight hours when one would expect larvae to be resting in a dark retreat, lair or niche hidden away from all sunlight. Thus is established in its detail the life cycle of P. pyralis from egg through larvae to pupae and adult, in all its complexity and wonder, revealing the mysteries of the firefly and presenting a host of additional questions for the pondering mind. Photo by Terry Lynch.
Figure Z14. Two small sections of earthworm E1 and E2 were fed to P. pyralis larvae which have been kept in a darkened rearing chamber and were photographed 22 hours later. A large, well formed, tight knit aggregate AL is seen under the cover slip with some larvae feeding F. Aggregated larvae appear to be in close contact, each larva touching other larvae. One larva L1 appears to be foraging and at 17:00 hours this world represent daylight activity; however, larvae are being maintained in vitro in foil wrapped chamber and can not see daylight periods. L2 has ventured away from the aggregate, perhaps to moult. A previously removed section of dried earthworm had a distinct hole in its side, apparently where larvae had eaten away flesh so they could burrow into the earthworm to feed. Larvae are continuing to hatch from eggs and join the aggregate some 49 days after the egg collection began and 21 days after first feeding behavior of earthworms was recorded.
The fact aggregates grow over time as more larvae hatch from eggs is very significant as should this occur in vivo it would indicate the possibility of large groups of larvae forming. In areas where P. pyralis or related species which exhibit aggregation are extremely abundant, these aggregates could become quite large. Over time this would contribute to the strength of the population. Year after year this behavior would enable large populations to build and become the dominate species of firefly which is probably why P. pyralis has often been observed in large numbers during the peak periods of adult activity. But what these large populations represent is not purely solitary behavior so much as the emergence and swarming of closely related members of a group. This also explains how destroying the habitat of P. pyralis through building parking lots, roads, housing complexes, shopping centers and other structures without regard to preserving forested areas can wipe out entire populations; as destroying the habitat kills all the aggregates of larvae in a single instance of earth moving. Once gone, firefly populations are gone forever and have no opportunity to replenish themselves as the forest floors and meadows they depend upon to live and grow as larvae in aggregates are forever lost to the bull dozers. Hence to preserve fireflies, especially those species which exhibit aggregation as larvae, it is imperative to preserve the habitat of the larvae. The concrete jungles of America, its asphalt highways and urban sprawl, is killing the fireflies. Their only salvation is our leaving some areas untouched and free of human molestation of the environment. Photo by Terry Lynch.
Figure Z15. At 07:22 hours (more than one hour after sunrise) and some six hours after having been given a new section of earthworm E1, P. pyralis larvae were observed clustered around the earthworm feeding. At least three sizes of larvae were observed as indicated by L1, L2 and L3. Old sections of earthworm E2 had dried out and were not moldy; in fact, water was added to the rearing chamber at the same time the earthworm section was presented, given the soil was becoming dry. Initially larvae were in a tight aggregate beneath the 2.0 cm. square cover slip C; then after adding water and a fresh earthworm section, larvae were kept in complete darkness. They emerged from beneath cover slip to feed in an outstanding display of group feeding behavior. Another larvae was observed burrowed 5.0 cm. beneath the soil (not shown). Perhaps in their search for food individuals burrow through tiny cracks and crevices in the soil, which may take them far away from established aggregates. This observation tends to recreate behavior of larvae exposed to dry conditions followed by rain. Larvae aggregates may become active after water drenches them; they then forage for food and eat. Such behavior would suggest that the naturalist hunting for larvae may enjoy the greatest success at night after rainy weather. Photo by Terry Lynch.
Figure Z16. Approximately 57 hours after last feeding and addition of water to the drying soil of the rearing chamber, larvae have begun to disperse and burrow beneath the soil. Larvae were observed to a depth of 5.0 cm. Here larvae are shown just beneath the surface at L1, at 2.5 cm. depth L2 and at 4.5 cm. depth L3. In one burrow (not shown) as many as three larvae were observed aggregated just below the surface in a tiny chamber. Four larvae were observed foraging upon the surface of the soil and the earthworm section last provided had been reduced to a much smaller slimy mass of digested material.
The largest larvae were measured and calculated to be 4.7 mm. in length. This is a 1.9 mm increase in length over larvae newly hatched from eggs which measured 2.8 mm. in length. Taking the length of an adult female as 15.0 mm., equating this to the maximum length of a larvae before pupation, estimating a constant growth rate from the interval measured, it is calculated that minimum number of days from egg to adult will be 290 days! This does not take into account slower growth over winter months due to low temperatures, or time for pupation. However, this calculation does predict larvae of P. pyralis will mature to adults with in a year. Should this be true it puts to rest the myth that larvae of this species require more than one year to mature.
Burrowing behavior of P. pyralis larvae indicated the need to use deep containers of soil when rearing larvae of P. pyralis. Burrowing also indicates that in vivo larvae may tend to disperse widely through the soil, only forming aggregates when they happen upon each other by chance or in attraction to each other's glow (glow serving perhaps as the manner in which larvae recognize each other). Burrowing also would enable larvae to survive cold winter temperatures and surface freezing conditions. Burrowing may also make larvae less vulnerable to surface predators, like spiders. It is certainly interesting that early instar larvae are able to burrow through compacted soil, a fact which also puts them in the same area of the soil where earthworms, their primary prey, may be burrowing. Note: I first observed early instar Photinid larvae burrowing in loose sandy Florida soil in 1971, but did not know with certainty the early instar larvae of P. pyralis are able to burrow into the hard, compact clay soil of Alabama until this present series of observations. Obviously the larvae fill up on fluid from the digested earthworm and this enables them to burrow into even hard, compacted soil which has become soaked, as might occur after a rain shower. Photo by Terry Lynch.
Figure Z17. Predaceous behavior of P. pyralis was observed on August 26, 2001, by placing four live "red wiggler" earthworms 3 - 5+ mm in length inside rearing chamber. As soon as earthworms crawled beneath the cover slip where several larvae were aggregated, earthworms were attacked as indicated by the immediate contraction, twisting and wiggling of the earthworms. Soon one larva L was observed using its anal appendage to attach itself to an earthworm (A above). When a larva would apparently bite an earthworm, the earthworm would roll and twist in a defensive effort to free itself from the attached, attacking larva. In B above larva L is seen riding upon an earthworm many times its size. In C above the earthworm tries to escape by crawling up out of the rearing chamber as the attacking larvae L clings with its anal appendage to the earthworm.
This sequence of observations indicates that P. pyralis larvae use their anal appendage to attach themselves to earthworms, then biting and riding them until their paralytic venom takes effect. As an earthworm struggles with an attached larva, going into spiral rolls, it was possible to see the larva glowing brightly, perhaps a signal to other larvae that an earthworm had been located and was under attack. Because a larva glows its lantern very brightly while attacking a struggling earthworm which twists, turns and makes spiral rolls, it is probable bright lantern glow serves to signal other larvae within sight that an earthworm is being attacked. Then other larvae seeing the bright glow may come to assist in the attack, that a group of larvae may more easily secure prey and share in the resulting feast.
Although this predaceous behavior was observed in virtro it is certainly reasonable to suspect it occurs in vivo, demonstrating perhaps one of the most remarkable functions of the anal appendage, to serve as a thousand tiny grappling hooks in securing itself to a prey many times its size, while the larva rides the struggling earthworm, which soon succumbs and is paralyzed by the larva's powerful venom, then to be digested and eaten alive! Though I had long suspected P. pyralis larvae may use their anal appendages in this manner, it is quite spectacular to see a tiny larvae only 4.8 mm in length secure itself to an earthworm over 50 mm in length, some ten time its size!
This sequence of observations and photographs leaves no doubt to the fact that P. pyralis larvae are predators of earthworms. In the still of the night there are firefly larvae preying upon earthworms, hooking on to the earthworms with their anal appendages and riding the struggling earthworms, the agitation of the struggle causing the larvae to glow brightly, perhaps serving as a beacon, signaling other larvae that food has been located, as if to say, "Come join in the kill; come join in the feast!" Photo by Terry Lynch.
Figure Z18. Approximately 16.75 hours after feeding four "red wiggler" earthworms to P. pyralis larvae this photograph shows the paralyzing effect of the larvae's digestive venom. Three earthworms, E1, E2 and E3 had contracted and were clustered around the cover slip. Larvae L1 and L2 were observed feeding upon E2 before the earthworm was disturbed to determine that it was alive, but the earthworm's reactions and motion seemed much reduced from that of a healthy, highly active earthworm. A fourth earthworm (not shown) was found having managed to crawl up upon the glass surface of the rearing chamber to momentarily escape larvae attack. Two larvae L3 and L4 were observed underneath the cover slip, not feeding. Two more larvae (not shown) were observed foraging upon the soil surface.
This large mass of earthworms, some 30-40 times the size of a single P. pyralis larvae, indicates that single early instar larvae would benefit from combining their digestive venoms in attack of large earthworms. Of course in vivo early instar larvae may be able to find much smaller earthworms such that a single larvae might more readily paralyze its prey. Certainly in vitro observations indicate the larvae's digestive venom tends to cause contractions in earthworms so that the prey tend to become motionless and can not escape. The combined efforts of several early instar larvae feeding upon a much larger earthworm immobilizes the earthworm, paralyzing it, permitting the larvae to eat its prey alive!
Also shown are an old section of earthworm EM with mold beginning to form. Moist soil is adhering to the underside of the cover slip obscuring whatever activity larvae may be engaged in beneath the soil. Other larvae were observed still burrowed in soil elsewhere in the rearing chamber begging the question, do larvae retreat to the safety and seclusion of soil burrow enclaves, then venture forth to the surface to hunt for food, perhaps after moulting? Or do these subsurface larvae simply wait until an earthworm nears their retreat, perhaps being able to feel or sense its passage through the soil, then venture forth to hunt and attack their prey? Photo by Terry Lynch.
Figure Z19. 11 Oct. 2001. A number of P. pyralis larvae in a tight aggregate AGG cell 4.5 - 9.0 mm beneath the surface of the soil. The continued aggregation of larvae in lairs, chambers or cells which they burrow out beneath the soil is good evidence that this behavior is the result of a strong attraction each larvae has for every other larvae, probably the result of larvae being attracted to the glow of their lanterns and/or the tactile stimuli of being in contact with other larvae. This observation was made at 03:20 hrs. after keeping larvae in a rearing chamber (quart jar of soil) wrapped with aluminum foil to prevent light from reaching the larvae. This is approximately 10-11 weeks into the growth of larvae, given the age of larvae is mixed, some having emerged from eggs earlier than others. Rearing consist of routinely adding a small earthworm to the chamber along with a few drops of distilled water and setting the rearing chamber aside undisturbed. The Photo by Terry Lynch.
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by the author. In any related investigations please site the author's works just
as you would had it appeared in a scientific journal. Thank you.
