They populate the bottom of the ponds, hide under the stones of the streams, slip into the rushes of the ponds... The carrion beetle, the wood dragger, the alder beetle, the carpenter beetle, the caddisfly form a family of common insects, with a half aquatic, half aerial life cycle.
A mason insect
It reveals its presence when it moves, some debris of the pond seeming to set in motion. The larva of Phrygane lives in small tubes from 2 to 4 cm long, made of various materials. Of the group of Integripalpia these mobile Trichoptera of greenish tint let exceed of their sheath a short and broad head with the eyes little marked, with the short antennas, with the crushing mouth. The six pairs of legs are visible, the first pair rather short, the others long and thin. The elongated abdomen ends with a pair of hooks hidden in the sheath.
Cousins of the butterflies, the Phryganes do not weave a nymphal cocoon but a permanent shelter.
A house of silk and eclectic materials
The small larvae of caddisflies build their first shelter very early. The front legs seize and sort the available organic and mineral materials, the mouth apparatus cuts them, adjusts them. Two specific glands near the mouth produce a liquid and sticky silk, cementing the whole, lining the inside of the tube for an optimal comfort.
The finished sleeve forms a funnel and remains open at both ends. Blending into the environment, it offers perfect camouflage and effective protection. It will be different according to the materials available, and especially according to the species of caddisflies, each one having its preferences.
To each species its sheath
If certain species of caddisflies make a sheath of leaves cut in large pieces assembled in an elegant tiling, others opt for fine strips, assembled all bristled; others will choose twigs cut and piled up in regular spiral; others still will agglomerate shells of planorbe.
To better resist the current, the caddisflies will weight themselves with tiny pebbles. Each species will thus choose its style of sheath. If their favorite materials are missing, they will adapt, even choosing small pieces of plastic, beads, colored fabrics, identification by the sheath alone becoming uncertain.
A long year under water
Sheltered in their sheath, the larvae will live for most species a good year in unpolluted, well oxygenated water. The external gills, branched or digested, characteristic of each species, are arranged all along their abdomen and allow them to breathe the dissolved oxygen of water. This breathing is completed by a permeability of the tegument, and optimized by the creation of a current circulating between the two ends of the sheath. Conferring to this frame, in addition to the protective and camouflage role, a physiological function of first importance.
Diversified menus, a fast growth and an adjustable sheath
The larvae of caddisflies move on their four long locomotor legs. Detritus feeders in general, they scrape the substrates, crush the organic matter in decomposition. Helped by their front legs, they capture tiny particles in suspension, algae, invertebrates...
It will take them less than 4 months, up to 7 successive moults, to reach their maximum size. And with each moult, they will have to enlarge their sheath. Widening it on the head side while cutting the opposite small end.
A swimming nymph
Its maximum size reached, the larva is ready to metamorphose. It closes the two ends of its sheath with a membrane of woven silk, and pads its interior. The wing sheaths of the nymph develop, the long antennas of the future adult are folded in ventral position. Also appear dorsal spines, a pair of mandibles, swimming silks on the second pair of legs: the spines will enable him to release itself from its nymphal sheath, the mandibles to cut the trapdoor of exit, the silks to swim towards the surface. Where it will cling, one night, to an emerged substrate, then will metamorphose into adult, and will take its flight.
An adult with silk wings
Brownish to beige, the adult caddisflies are easily recognized. Elongated, of average size, 2 to 4 cm, they carry long and fine antennas projected towards the front, large well developed eyes. They could look like moths. But unlike their distant cousins they fold their four wings in the form of a roof and carry many bristles, sometimes long bangs. Trichoptera meaning silk wings. Also they do not have a spiral proboscis. Neither do they have mandibles. Just like Ephemera, the adult caddisflies do not eat, devoting themselves exclusively to their reproductive task.
An ephemeral life
The spring or summer appearance of caddisflies is short-lived, the time of a pause in a cave to complete their sexual maturity for some species, a few days for others. Briefly, males and females meet. The eggs will be laid in clusters on submerged plants, or just on the surface, as soon as they hatch the larvae enter the aquatic environment. The adults are stranded on the surface of the water, for the greatest delight of trout and other predators.
Common, diversified, caddisflies play an important role in aquatic habitats. Food source for many animals, fish, invertebrates, but also birds, they are also appreciated by fishermen, for the larvae as bait, the adults serving as a model for fly fishing.
