Saskatchewan Caddisflies (Trichoptera)
The Trichoptera is one of the most diverse orders of aquatic insects with over 7,000 species known world wide. In North America 22 families are represented by at least 1350 species. In Saskatchewan there are 15 families reported and more than 194 species. Probably the most interesting feature to the non-fishing general public regarding this group is the cases that many of the larvae construct out of various materials. Caddisflies are found in all types of aquatic habitats throughout Saskatchewan. The majority are intolerant of pollution and, as such, are valuable tools for monitoring organic and chemical contamination of habitats.
Trichoptera are holometabolous insects with a four-stage life cycle: egg, a five instar larva, pupa and adult. For many species development is arrested by diapause in one of the stages to synchronize the life cycle with favourable environmental conditions. For the majority of the species in the province only one generation is produced a year. However, there are exceptions that either have multiple generations a year while others take more than a year to complete the life cycle.
Females usually lay eggs directly into the water either singly or in masses. Some species lay their eggs above the water on overhanging vegetation while those inhabiting temporary ponds lay their eggs in dry pond basins. The larval stage is the only real significant feeding stage. Most species are omnivorous. The larvae scrape food off surfaces or shred decaying plant debris with their mandibles. Many species found in running water construct intricate nets of silk to filter food particles out of the water current. A few species are predaceous on other invertebrates during all or part of the larval stage. The pupal stage lasts for two to three weeks. The moth-like adults live from a few days to a number of months. In the latter case most of the time is spent in adult diapause.
With few exceptions larvae construct cases/retreats out of a variety of materials (pieces of plants, algae, sand grains, snail shells or entirely of silk). The materials are bound together with strands of silk secreted by the larva. The retreats are of 4 basic types. The family Glossosomatidae makes a mobile retreat of rock fragments that resemble tortoise shells. Final instars of the tiny Hydroptilidae build purse or barrel shaped cases of algal cells, sand grains or silk. A number of groups, including the families Phryganeidae, Brachycentridae and Limnephilidae construct portable retreats that are tubular. A further retreat type is the fixed retreats typical of the Hydropsychidae. These retreats are constructed of sand grains and organic debris and are attached to rocks or logs in running water or along rocky wave-washed lake shores. The anterior opening has a silk net covering that acts as a filter to remove food particles from the water which the larva periodically eats and replaces. The family Helicopsychidae makes a sand grain retreat that looks like a small snail shell.
Below is a family key to the larvae of caddisflies found in Saskatchewan. It has been modified from Smith (1984) and Clifford (1991).
1a: Body of larvae very curved and case snail shell-like.--Helicopsychidae
1b: Larvae not curved. Cases in other shapes or case less.--Go to 2
2b: Dorsal part of each meso and metathoracic segments with large areas of membranous cuticle on at least the last thoracic segment (metathorax). (A: Entirely membranous meso and metathorax. B: Large plates on mesothorax and small plates on metathorax.)--4
3a: Abdominal gills many branched. Mature larvae greater than 6 mm long. Larvae build retreats attached to rocks or other debris rather than cases.--Hydropsychidae
3b: Mature larvae less than 6 mm long. Gills single or not evident. Cases are made of a variety of materials including, sand grains, silk, and algae.--Hydroptilidae
4a: Antennae "long", about 6 times as long as wide.--Some Leptoceridae
6a: Abdominal segment one has a dorsal hump and lateral humps. (d.h.= dorsal hump;l.h.= lateral hump; mes= mesonotum; met= metatnotum).--Phryganeidae
6b: No humps on abdominal segment one.--7
7a: Anal proleg short and broadly joined with abdominal segment nine. Claw with one or more dorsal accessory hooks .--Glossosomatidae
7b: Anal proleg longer and not broadly joined to segment nine.--8
8a: A plate present on dorsal surface of abdominal segment nine. Branched gills present or absent.--Rhyacophilidae
8b: No plate on abdominal segment nine. Gills never branched.--9
9a: Upper lip of mouth (labrum) in the form of a "T".--Philopotomatidae
9b: Labrum not "T" shaped.--10
10a: Protrochantin pointed toward apex. (Best viewed obliquely to see the shape.).--Polycentropodidae
10b: Protrochantin in the shape of a hatchet or meat cleaver-like.--Psychomyiidae
11a: Antennae short. Second thoracic segment (mesothorax) with distinctive markings.--Some Leptoceridae
11b: Antenne short. No distintive markings on mesothorax.--12
12a: No dorsal hump on abdominal segment one.--13
13a: Antenna very close to the front margin of the eye. Abdominal segment one with lateral humps present. Mature larvae make square cases.--Lepidostomatidae
13b: Antenna about half way between front corner of eye and the front the the head. Abdominal segment one lacking. In some species the mature larvae construct square cases.--Brachycentridae
14a: Claw of hindlegs different from the other two pairs. Either short haired stump, or, a long fine claw with accessory hair. Cases made of sand grain with a "porch roof" overhanging the anterior opening.--Molannidae
14b: Hind claws similar in structure as the other claws. Cases come in a variety of shapes and made from many different types of materials.--Limnephilidae
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