Vol. 15 Issue 1, Spring 2010
By Mary LoPresti
While the average person (myself included) may not be able to handle the sight of a creepy-crawly such as the stonefly, many scientists and fishermen have learned to appreciate this four-winged insect.
Stoneflies experience an incomplete metamorphosis, which means, like humans, they keep close to the same body shape most of their life. After hatching from their egg, the stonefly becomes a nymph (young stonefly) and then an adult. The appearance of the nymph differs from an adult in the emergence of wing pads instead of wings and in the length of their bodies and tails. While the nymph can measure 0.5 to 5 centimeters in length and have two long tails, the adult measures up to 2½ inches long and has two short tails. They each have two long antennae, widely spaced eyes, gills found on the throat or at the base of the legs and abdomen, and three pairs of crablike legs with claws.
Many species of stonefly live on or under submerged and exposed stones in or along streams. Scientists have discovered that stoneflies are typically found living in the flowing waters of cool streams (under 77° F). Cooler, faster-moving water carries more oxygen than warm water. Like many other aquatic organisms, as water moves past the stonefly’s gills, dissolved oxygen in the form of microscopic bubbles is transferred from the water to its blood.
Stoneflies help keep other insect populations in check. While a hungry stonefly may chomp on a plant once in a while, they are mainly carnivorous and feast on insects such as midges, blackflies, mayflies, and other stoneflies. They find themselves prey to salamanders, birds, and fish. Trout in particular find them exceptionally appealing.
Nymphs are very poor swimmers; therefore they use their crab-like legs to crawl along the streambed. They easily become victims of trout when they lose their footing in the current. While nymphs are available to fish year round, stonefly adults live only 2 to 3 weeks. During mating season, clouds of stoneflies congregate together above streams, frenzied in their search for a mate. Some stoneflies, after mating or laying eggs, fall spent on the water. The sight of females laying eggs in the water or in the air so the eggs drop to the water is like fast-food heaven to trout. For this reason, fishermen attempt to imitate the commotion of stoneflies when casting their lines or when manufacturing fishing lures.
http://www.bcadventure.com/adventure/angling/bugs/stonefly/stonefly.phtml : Article by Ron Newman