| Major Group: Insecta
Caddisfly larvae are sometimes called “sticks that walk”. Many larvae construct portable silk cases, often incorporating organic and inorganic materials from the surrounding stream habitat, so it is important when collecting invertebrates to carefully investigate apparent sticks, stems and sand grain masses for movement, legs and heads.
| Ecology: Instream habitat: Caddisfly larvae occur in a wide range of habitats from fast flowing mountain streams and gently flowing lowland creeks to freshwater ponds, dams, lakes and reservoirs. Slower, warmer, less oxygenated waters with loose sandy or silty substrata tend to have a lower species diversity.
Feeding ecology: Case making larvae may graze on algae on rocks, chew on submerged plants or shred detritus in leaf packs. Retreat making larvae have nets attached to the end of the retreat, in the flow, to catch food and are mostly associated with herbivores and filter feeders catching fine organic particles. Free living larvae are mostly predators but some species are omnivores or change their diet as they mature. Hydrobiosidae species use a silk thread to anchor to rocks in fast flows while they hunt.
Habit: Trichopteran larvae exhibit a range of habits from crawlers to active swimmers including case making, net spinning and free living larvae. In Hydroptilidae species, only final instar larvae are case makers, the earlier instars are free living. Across the families, case materials range from only the silk itself or silk with sand grains, leaves or wood, reflecting the surrounding habitat. Members of the same species tend to build similar cases in terms of size, orientation and type of incorporated materials. Hooked anal prolegs anchor the larva to the case. Some species swim with portable cases, other species use silk to anchor the case to the substrata creating a fixed retreat (but not all retreats are technically cases). As a larva grows more material is added to the case at the front end. Some Trichopteran species construct tubular retreats along the surfaces of rocks or within stream bed sediments.
Life history: Trichopteran adults are terrestrial and short lived, active flyers with reduced mouthparts. Egg, larval and pupal stages are all aquatic with the larval stage being the longest. Adults mate in flight, on the ground or in riparian vegetation. Spherical or elliptical eggs are simply dropped over the water or placed on objects protruding from or near to the water and some females even crawl under the water to deposit a sticky gelatinous egg mass on the substratum or a submerged plant. One female can lay twenty to several hundred eggs as a mass, in strings or individually. Eggs hatch within three to twenty five days. There are five to seven larval instars between egg and pupal stage. At pupation, the final instar larva seeks out a sheltered part of the stream channel and then either spins silk around the old larval case, sealing each end, or constructs a specific silk pupal covering (free living larvae). The non-feeding pupal stage lasts for fifteen to twenty five days after which the pupa chews out of the case and swims to an emergent plant or rock where the adult emerges. The peak emergence time in Australia is December to January.
Examples of portable cases:
|Information Sources: Dean et al 2004, Neboiss 1991, Williams 1980, Ingram et al 1997, Davis & Christidis 1997, Zborowski & Storey 1995
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