Stoneflies spend the larval stage of their life in streams. When the larvae mature, they crawl out of the streams they grew up in, split their larval skins and emerge as winged adults, ready to mate. Stoneflies are unique among aquatic insects in that there are different species that emerge in all months of the year. Most species mature in warmer months, but some do so during warm spells in winter and there are two families (referred to as winter stoneflies) that emerge only at this time of year, perhaps because of the scarcity of predators.
Recently, perhaps due to the warm weather this past weekend, large numbers of stoneflies emerged. In places, the snowy banks of open streams were littered with half-inch adult stoneflies whose new skins were drying. This entomological exodus from the water typically takes place at night, to avoid being eaten by terrestrial insectivores and birds. After their adult skin dries, winter stoneflies can be seen crawling on top of the snow as they search for a mate.
In many species, male and females locate each other by tapping the tip of their abdomen upon the substrate, a process referred to as “drumming.” Any stoneflies in contact with that substrate will feel the vibrations of this drumming. Male and female drumming patterns are specific for each species and for each sex. Male stoneflies initiate drumming and females answer. This means of auditory communication is closely related to the “songs” of crickets, grasshoppers and katydids. The difference is that the sound waves of the terrestrial insect songs travel through the air and are loud enough for humans to hear, whereas the sound waves of stonefly drumming travels through a solid medium and is inaudible to us.
The diet of both Cedar and Bohemian Waxwings is primarily sugary fruits throughout most of year. Research shows that they can subsist on this diet exclusively for as many as 18 days. However, in winter when feeding on fruits, they also feed on buds and available insects. In warmer months, waxwings will fly out over water from exposed perches, much like flycatchers, and snatch emerging aquatic insects such as mosquitoes, midges, mayflies, caddisflies and dragonflies out of the air. They also glean for vegetation-borne insect prey, such as scale insects. At this time of year they are taking advantage of winter stonefly hatches over open streams. (photos: bohemian waxwing & stonefly)
It seems early, especially with feet of snow still on the ground, to be seeing insects flying around, but some have actually been present all winter. An order of insects (Plecoptera) known as stoneflies spends its youth (one to four years) living in streams before emerging as winged adults. Some of these species, referred to as winter stoneflies, emerge from January through April, providing food for early-returning, insect-eating migrants, such as Eastern Phoebes, Tree Swallows and Red-winged Blackbirds. Stoneflies only live a few weeks, during which time they mate and lay eggs. Some do not feed, and others consume plant material. Because stoneflies are intolerant of polluted water, if you see one it’s a good indication that the water quality of the stream that it came from is excellent.
There’s no denying the arrival of spring, even when the snow is still up to your knees in the woods, if Eastern Phoebes are back! This member of the flycatcher family is one of our earliest returning and nesting migrants, arriving on its breeding grounds in late March and early April. One might wonder what this insect-eating bird subsists on at this time of year. Wasps, bees, beetles and butterflies are not in great supply. Fortunately, there are some insects around, including stoneflies – aquatic insects, some of which mature and emerge from streams in the winter and early spring. When insects aren’t plentiful (in fall, winter and early spring) phoebes will eat small fruits, but they only make up about 11% of their diet.