Glow-WORM
PHENGODIDAE (Phengodid Beetle) (Glow-Worm)
(Including Pseudophengodidae).
Residents may recall seeing a strange green glowing dot on the ground during the rainy season. Although this phenomena may be caused by hallucinogenics, it is also caused by the luminescent glow of this insect which we have temporarily called a glow-worm until it's true name is verified. The glow is most likely used to attract a mate and is similar in appearance to glow created by fire-flies on the east coast. This specimen was collected outside last winter after seeing it's green glowing butt and then was brought inside for a photo shoot.
Classification. Polyphaga: Elateriformia.
Distribution. Phengodidae are distributed throughout the New World from extreme southern Canada to Chile.
Biogeographic regions: Nearctic, Neotropical.
Biology. Larval and female Phengodidae are predators, feeding on millipedes and other arthropods occurring in soil and litter.
The winged males, which are often attracted to lights at night, are short-lived and probably do not feed. Females are much larger than the males and are completely larviform.
Males may be luminescent, but females and larvae have a series of luminescent organs on trunk segments, which emit yellow or green light, and sometimes an additional head organ, which emits red light.
ADDITIONAL INTERESTING INFO ON GLOW-WORMS
Millipedes are among the best protected of arthropods.
Most possess defensive glands, in the form of integumental sacs arranged segmentally along the length of the body, from which they discharge such diverse toxins as 1,4-benzoquinones, phenols, hydrogen cyanide, quinazolinones, and alkaloids (1).
Anyone who has handled millipedes, particularly the large 1,4-benzoquinone-discharging members of the orders Spirobolida and Spirosteptida, knows that these animals can eject their secretion in copious amounts in response to even mild provocation.
Not surprisingly, predators are deterred by these fluids (1).
There is, however, one group of predators, the larvae of beetles of the family Phengodidae, that feeds on millipedes as a matter of routine. Although worm-like and seemingly innocuous, phengodid larvae are voracious hunters capable of killing millipedes larger than themselves.
Their predation strategy is unique and has been described in some detail by Tiemann (2) for Zarhipis integripennis, a phengodid from California. When a millipede comes to within proximity of a Z. integripennis larva, the larva races alongside it, mounts it, and throws a body coil around the millipede's front end.
It then pierces the millipede's neck membrane with its mouth parts, and effects an action that causes the millipede to become quickly immobilized. The larva then burrows underground beside the millipede, only to emerge after a time to commence feeding.
It consumes the soft insides of the millipede only, predigesting the millipede's tissues with its own enteric fluids, which it apparently regurgitates while feeding. Only the millipede's skeletal parts remain uneaten after the meal.
What was most intriguing about Tiemann's account is that the millipedes seemed not to discharge their defensive glands during the attack. Did the larvae kill the millipedes in some special way that kept them from activating their defenses?
Tiemann speculates that the millipedes might have their nerve cord severed when the larvae pierced their neck membrane, but he presents no supporting evidence. Also unanswered was the question of the ultimate fate of the secretion.
Are the glands not inevitably ruptured when the larvae feed on the millipedes' contents? Why are the larvae not then deterred? Do they ingest the secretion?
(Pterotus obscuripennis)
displaying bio-luminescence at night.
Tillamook State Forest,
coastal mountains, Oregon, USA
Giant Glowworm Beetles
(A Taxonomic Survey of Lanterns and their Use)
We will look into explanations for the phengodid peculiarity of subterranean light after introducing our North American giant glowworm fauna. The most commonly collected species belong to the widespread genus Phengodes and the western/southwestern genus Zarhipis. Euryopa is a less known member of the same tribe, the phengodini. The obscure ranks of the tribe Mastinocerini consist of seldom seen and little known genera such as Cenophengus, Paraptorthodius, Distremocephalus and Mastinocerus. Due to the variety of forms within populations, the number of North American species is open to debate. In Zarhipis, there are at least three species. Z. integripennis is the most widely distributed species, being found in western Washington and Oregon, throughout California to the southern half of Arizona and Baja Mexico. In Arizona it is restricted to mountains and appears to favor somewhat moister regions than Z. truncaticeps, which is a desert dweller, found in Arizona, California and New Mexico, and possibly southwestern Texas. Z. tiemanni is most abundant in the China Lake district of California, but has been collected in Nevada and Arizona as well.
All stages of the phengodid life cycle bear lights. Embryos can be seen glowing inside the egg and the larvae and larviform females sport multiple light organs, the pattern varying somewhat among species. In Zarhipis and Phengodes there are points of light on the sides of the second through twelfth body segments and stripes of light shine between the segments.
Zarhipis males have a feeble luminescence that requires allowing the eyes to become dark-adapted before it can be seen.
The value of luminescence to a beetle larva is a mystery. It is particularly puzzling when the larva lives and glows underground. A number of reasons for carrying lights have been proposed, but the first one to consider is aposematism” or “warning coloration.” The great 19th century naturalists, particularly H. W. Bates, pointed out that some insects were distasteful to birds and other predators and that poisonous species often “advertise” their unpalatability with bright warning colors.
When roughly handled, Z. integripennis secretes a clear amber fluid from U-shaped pores on abdominal segments 2-9.
All of this at least suggests a chemical defense that might be advertised by phengodid glows. A bit of circumstantial evidence is that the lights of many glowworms brighten or light up when the insect is disturbed. They may be intensifying their warning as danger approaches — just as a rattlesnake may increase the frequency of its buzzes.
Even if phengodids pack a potent chemical punch, could a warning signal that can’t be sent through the surrounding soil be of any use? Well, yes it could, if it were the first thing a burrowing predator saw as it broke in upon its prey. To insure being noticed an underground light display should be spread over the surface of the insect. Phengodids tend to have numerous light organs dispersed over their bodies.
In our native Zarhipis adult females, lights probably continue to function for the same reason that they shine in the larvae - whatever that may be! Males have small eyes and mating occurs in daylight.
Adult female glowworms
(beetles of the family Phengodidae) retain their larval form and can be mistaken for millipedes. To make matters worse, they eat millipedes by biting off the head and eating their way through the body. If you catch one of these beetles at the right time you will see a millipede with one end glowing!
Female glowworm (Zarhipis sp.) in normal light and glowing in the dark.
Photograph courtesy of Nancy Baumeister.
