The Mystery Photo was of a caddisfly’s egg mass which had been deposited on the leaf of a Turtlehead plant that was growing adjacent to the water, so that when the eggs hatch, the larvae will drop straight down into the water. (Congratulations to “bcottam2014,” the first person to correctly identify the Mystery Photo!)
Almost all caddisflies lay their eggs in the water, but in New England there is a family of northern case makers (Limnephilidae) whose members deposit an egg mass above the water on vegetation (see photo). After hatching and dropping into the water, these caddisflies will spend anywhere from two or three months to two years as aquatic larvae and pupae, emerging as adults with about a thirty day lifespan.
While they are larvae, most northern case-making caddisflies have silk glands with which they construct portable cases or attached retreats. Each species of caddisfly builds the same type of case, out of similar material, thus, it is possible to identify the species of caddisfly you’ve encountered from the appearance of its case. Some species use pebbles, some bits of leaves, some sticks. Vegetative material must be chewed into just the right size and shape pieces. The caddisflies use these cases as a source of camouflage, physical protection and as a means of acquiring food. When it comes time to pupate, they build cocoons within their cases.
Emergence of adults eventually takes place and for the next month or so they live a terrestrial life. Like their close relatives, butterflies and moths, adult caddisflies have wings, but they are easily distinguishable from moths and butterflies due to the tent-like slant the caddisfly holds its wings in when not flying. (Photo: caddisfly larvae hatching from egg mass; inset – older caddisfly larva inside pebble case it built)
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