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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Most caddisflies lay their eggs in or near ponds or streams. A very few species (in the family of northern case makers, Limnephilidae) deposit their eggs above the water on aquatic vegetation in a one- to-two-inch-long mass of jelly (some species’ eggs lack the jelly). Up to 800 eggs (the tan spots within the jelly in yesterday’s post) are laid at one time in one mass. Depending on the species, the eggs take from several weeks up to ten months to hatch. These masses are usually situated so that once the eggs hatch, the larvae will drop down into the water, where they will spend their larval and pupal stages.
Caddisflies are closely related to butterflies and moths, and one of the features they have in common is that the larvae have silk glands in their lower lip. Thanks to the ability to spin silk, the caddisfly larvae build portable cases or attached retreats out of natural material that is available. Some species build elongate tubes out of pieces of plants, sand, sticks or pebbles and reside in them while they drag them along with them wherever they go. Other species attach their cases with silk to crevices in or the bottom of stones in streams. Each species of caddisfly larva always constructs the same type of case, so that you can often tell the genus or even species of caddisfly by the appearance of its case.
The larval stage of a caddisfly can last two to three months or up to two years, depending on the species. Most species spend the winter as active larvae. When it is ready to pupate, the larva attaches its case with silk to something immoveable, such as a large rock. Inside its case, the larva spins a cocoon and eventually pupates inside of it. In two to three weeks the sharp-jawed pupa cuts its way out of its cocoon and floats up to the surface of the water where it emerges as a winged adult, often using its pupal skin as a raft for support during this process. Adult caddisflies live for about 30 days, during which time the males form mating swarms to attract females. After mating takes place, the egg-laying begins.
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