Dobsonfly

A male dobsonfly, despite its terrifying pair of curved jaws up to three centimetres long, is essentially harmless. The mandibles are so long that the muscles closing them have very little mechanical advantage at the tip, so a male trying to pinch a finger can barely break the skin — it feels like a firm nip at most. The female is the opposite — her jaws are short, stubby, and powerful, and a female that is roughly handled can bite hard enough to draw blood and hold on. Neither sex is venomous, aggressive, or a threat beyond that. The aquatic larva, the hellgrammite, also has strong jaws and will bite a careless angler, which is one origin of the name "toe-biter" (a name it shares with the giant water bug).

They are used entirely in male-to-male combat and in courtship, not for feeding or defence. When two males meet, they fence and grapple with the long mandibles, each trying to grip, lever, and flip his rival off a perch, and the loser retreats — the winner gets to court nearby females. During mating, the male uses the same jaws to reach forward over the female's back and clasp her firmly across the base of the wings, holding the pair together through a mating that can last many minutes to hours. Because the jaws never need to exert force at close range or crush anything, sexual selection has been free to exaggerate their length as a signal of male quality, much like a stag's antlers or a fiddler crab's claw.

A hellgrammite is the larva of a dobsonfly — a flattened, dark, segmented, centipede-like grub up to about 8 centimetres long, with strong pincer jaws, a pair of hooked appendages at the tail, and rows of feathery gills along the sides. It lives for one to three years clinging to the undersides of rocks in fast, clean stream riffles, where it is one of the top invertebrate predators. Anglers prize hellgrammites as bait for smallmouth bass, trout, catfish, and panfish because they are tough, active on the hook, large, and a natural food item that fish key in on. They are collected by holding a net downstream and turning over rocks, and in some places they are sold commercially, though over-collection and stream pollution have reduced them in parts of their range.

Very briefly, and almost nothing. After spending years as an aquatic larva and then a few weeks as a pupa in streamside soil, the adult dobsonfly emerges, and its entire winged life lasts only about three days to a week. Adults are essentially a dispersal-and-mating stage. Their mouthparts are reduced, and while they may sip a little nectar, tree sap, or water, most do not feed at all and simply live off the fat reserves built up by the larva. They are nocturnal, fly weakly, are strongly attracted to lights, and spend the daytime resting motionless on streamside trees, rocks, and walls with their large wings folded tent-like over the body.