"Both male and female adults of
P. borealis are 11-19mm long (Green 1957). Their elytra are dark brown with very narrow to obliterated pale margins and a pale elytral suture. The pronotum is subpentagonal in shape, lighter than the elytra, with a dark median vitta (stripe) and sometimes with rosy patches. The lateral edges of the pronotum also have dark vittae, which are often pale and difficult to notice in some specimens.
Pyractomena borealis can be differentiated from all other Alberta fireflies, except
P. dispersa, by the presence of light organs, which appear as two pale, enamel-like ventral abdominal segments in the male. The female has enamel-like organs confined to the edges of these same segments. The extent of secondary elytral pubescence is useful in differentiating
P. borealis from other
Pyractomena species. In
Pyractomena borealis, this secondary elytral pubescence (very tiny hairs, which give the elytra a dusty appearance) is present on most of the dorsal elytral surface, extending from the apex to about the basal quarter. In some specimens, this pubescence extends further, with only the basal 1/6th of each elytron appearing glabrous.
Pyractomena borealis larvae are campodeiform, 17-22mm long in the 5th (last) instar, quite hard bodied, and somewhat flattened dorsoventrally. First instar larvae measure 3.5-4.5mm (Archangelsky 1998). Larval colour ranges from dark brown to brick red, and the pattern can be variegated (Arnett 2001). The abdomen narrows gradually to the 10th (last) segment, which is very small and contains the larval hold-fast organ. This structure is like a posterior foot; it has 10 protractible finger-like structures, each covered in tiny hooks, which allow the larvae to grasp surfaces or objects. The head of these larvae is long and narrow, and can be fully retracted into the thorax (Archangelsky 1998).
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Habitat
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Wet, wooded areas.
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Life Cycle
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Pyractomena borealis overwinters as a 5th instar larvae. The overwintering position is usually on a tree trunk some distance from the ground, and often on the southern exposure in the path of winter sunlight (Lloyd 1997). Larvae hang head down by their posterior hold-fast organ. The hold-fast organ is used not only to grip trees, but aids in larval movement and is used to groom the head after feeding, or the body after moving about in soil or debris. Pupation occurs in the early spring and lasts 4 to 5 days. Mating occurs very soon after adult emergence, and 3 to 4 days after mating a clutch of up to 100 eggs is laid in cracks in tree bark, or under loose pieces of bark. First instar larvae hatch after a month; subsequent larval moults occur in the same head-downward position that is exhibited during pupation and overwintering. Each instar, except the 5th, lasts less than 20 days (Archangelsky 1998). Both males and females are luminous.
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Trophic Strategy
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Larvae feed on snails. In the first three instars, multiple larvae may feed on a single snail, while later instars become solitary predators. The protractible head of P. borealis allows it to reach into narrow portions of a snail's shell, and the mandibles have an internal channel that is used to inject digestive fluids into the prey (Archangelsky 1998).
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Pyractomena borealis: Brief Summary
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Pyractomena borealis is a species of firefly in the beetle family Lampyridae. It is found in North America, where it has a very wide distribution, as it is known from Alberta east to the Maritime Provinces of Canada, and south to all US states east of the Mississippi River.
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