Caddis Fly – An Important Fly For Fly Fishermen

The Caddis fly, (Trichopetra) or sedges can be found anywhere there is fresh water. The drab coloured adults are moth-like however their body and wings are covered with hairs. Another distinguisihing feature is that the caddis do not have a coiled proboscis. Their wings are held over the body in a tent like fashion.

Mostly nocturnal, the adults hide in vegetation during the hours of daylight and are hard to find. Mating takes place at dusk, either in flight or on vegetation. Their bodies range in size from 2mm to 28mm (1.25 inches).

Caddis Fly

The caddisflies are an order  Trichoptera, of insects  with approximately 12,000 described species. Also called sedge-flies or rail-flies, there're small moth like insects having two pairs of hairy membranous wings They're closely related to Lepidoptera (moths and butterflies) which have scales on their wings, and both orders together form the superorder Amphiesmenoptera . Caddisflies have aquatic larvae and are within a wide variety of habitats such as streams, rivers, lakes, ponds, spring seeps, and temporary waters (vernal pools) The larvae of many species make protective cases of silk decorated with gravel, sand, twigs or other debris. The name "Trichoptera" comes from Greek  trich, "hair" + ptera, "wings".

Caddis Ecology

Although caddisflies can be present in waterbodies of varying qualities, species-rich caddisfly assemblages are generally thought to indicate clean water. Together    and mayflies  caddisflies feature importantly in bioassessment surveys of streams and other water bodies. Caddisfly species can be found in all feeding guilds in stream habitats, with some species being predators, leaf shredders, algal grazers, and collectors of particles from the watercolumn and benthos.

Caddisflies are considered underwater architects because many species use silk  for building throughout their larval life. Caddisflies may be loosely divided into three behavioral groups determined by this use of silk: retreat-making caddisflies, case-making caddisflies, and free-living caddisflies. Those that build retreats build a net or retreat from silk and other materials and apply it to catch food items just like algae, aquatic invertebrates and zooplankton from the flowing stream. Case-making caddisflies make portable cases using silk along with substrate materials as in small fragments of rock, sand, small pieces of twig, aquatic plants, or sometimes silk alone. Many use the retreats or cases throughout their larval life, adding to, or enlarging them as they grow. These may look very much like bagworm  cases, that happen to be constructed by various moth species that are not aquatic. Free-living caddisflies tend not to build retreats or carry portable cases until they're just ready to pupate.

Caddis Development

Many species of caddisfly larvae enter a stage of inactivity called the pupa stage for weeks or months after they mature but before emergence. Their emergence is then triggered by cooling water temperatures in the fall, effectively synchronizing the adult activity to generate mate-finding easier. In Northwestern US, caddisfly larvae within their gravel cases are called 'periwinkles'

Caddisfly pupation occurs very similar to pupation of Lepidoptera  That's, caddisflies  within a cocoon spun from silk. Caddisflies which build the portable cases attach their case to some underwater object, seal the front and rear apertures against predation though still allowing water flow, and pupate within it. Once fully developed, most pupal caddisflies cut through their cases having a special pair of mandibles, swim up towards the water surface, dispose of skin and then the now-obsolete gills and mandibles, and emerge as fully formed adults. In a minority of species, the pupae swim to shore (either below the water - see figure - or across the surface) and crawl out to emerge. Many of them are able to fly immediately after breaking from their pupal skin.

The adult stage of caddisflies, generally, is very short-lived, usually just one-2 weeks, but can sometimes last for two months. Most adults are non-feeding and are equipped mainly to mate. Once mated, the female caddisfly will often lay eggs (enclosed in a gelatinous mass) by attaching them above or below the water surface.  hatch in as little as three weeks.

Caddisflies in most temperate areas complete their lifecycles  in just one year. The general temperate-zone lifecycle pattern is one of larval feeding and growth in autumn, winter, and spring, with adult emergence between late spring and early fall, although the adult activity of some species peaks in the winter. Larvae are active in very cold water and can frequently be observed feeding under ice. In common with many aquatic insect species, many caddisfly adults emerge synchronously en masse. Such emergence patterns ensure that most caddisflies will encounter a member of the opposite sex within a timely fashion. Mass emergences of this nature are called 'hatches' by salmon and trout anglers, and salmonid fish species will frequently 'switch' to whatever species is emerging on a particular day. Anglers exploit this behavior by matching their artificial flies to the suitable fly.

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