Saskatchewan Aquatic Macroinvertebrates Guide

A picture guide to common Saskatchewan aquatic "bugs"

Many of the major groups of "bugs" can easily be identified with the naked eye. Even some species can be identified because they are so distinctive. Unfortunately other groups, such as the non-biting midges or bloodworms (Chironomidae: Diptera), are extremely difficult and require special techniques and a good microscope to identify them below the family level.

Most formal identifications of bugs, and other animals and plants, involve the use of dichotomous keys where choices are made between two character states, such as legs are black, or, legs are white. However, these are often long and drawn out documents that are hard to follow even for experienced users. A simpler way to identify the basic groups is to use a "Peterson's Guide" approach and comparing images with the specimen at hand. Below is an introductory picture guide to the Saskatchewan aquatic "bug" groups. For this guide once the "bug" is identified the reader can click on the navigation links for a more detailed account of the group.

Freshwater Sponges (Porifera) occur in clean standing or slowly flowing water. Sticks and rocks may appear to have yellowish green globs on them. Often these are algae but sometimes they are sponges. Close examination will reveal some holes in the surface and possibly a spongilla fly larva. Under magnifications of 200 times or more the various supporting structures (megascleres) can be seen.

Hydra (Cnidaria, Hydrozoa) are usually less than 20 mm long when fully extended. But when contracted they can shrink to just a few mm. Most are coloured a somewhat translucent white to reddish brown although some are green due algal cells in the body wall. For these reasons they are easily overlooked in their natural habitat unless the debris is examined carefully. They can sometimes be seen hanging from the water film. Hydra consist of an elongated baglike "body" from which about six or so tentacles emerge from around a dome shaped mouth region. Hydra can be found in all types of freshwater from roadside ditchs and sloughs to sheltered microhabitats in relatively fast flowing streams. They feed on small insect larvae and crustaceans which they capture using their long tentacles that are covered with cells (nematocysts) which eject threads to entangle the prey and others that sting the prey into submission. The tentacles then pull the prey to the mouth where it is engulfed. Often there will be "buds" of smaller hydra growing out of the body. This is a form of asexual reproduction.

Roundworms (Nematoda) can be seen as small white to clear threads about 1 cm long moving in their typical thrashing manner. They can be found anywhere in aquatic systems but are especially abundant in soft sediments with high organic content in both running and standing waters. Some, the family Mermithidae, are parasitic on aquatic insects, especially obvious in diptera fly larvae. The nematode can often be seen coiled within the body of the larva.

Aquatic Worms (Oligochaeta) are kin to the terrestrial earthworms. They are usually found in the bottom sediments of both running and standing waters. Many are bright red when alive. Most specimens are less than 2 cm long. Some species especially in the Tubifex sp. can occur in large numbers in areas of high organic pollution such as sewage outflows and lagoons. Identification for most requires mounting on slides and examining the patterns, numbers and types of setae (chaetae)

Leeches (Hirudinida) are easily recognised by their worm-like bodies with numerous segments. Size can range from 10 mm to 100 mm or more.

Snails & Limpets (Mollusca, Gastropoda) Snails have a coiled shell that has a spire or a simple flat coil like a rope. The "common pond snails" have the opening to the right when the spire is up. "Tadpole snails" have the opening on the left. Some families have a circular piece of shell, the operculum, which they can close the opening of the shell with. While limpets have the shell in the shape of a low cone. They are usually found in slowly flowing waters attached to submerged rocks, branches, vegetation or other debris.

Clams (Mollusca, Bivalvia) have two shells. Size ranges from a couple of mm across for the small "pea clams" to over 15 cm for some of the larger types of "floaters" and "heal splitters". Representatives are found in all types of waters.

Crayfish (Decapoda) are lobster-like. They can often be seen scuttling between the rocks of slow moving streams and rivers or in the shallows of lakes.

Scuds (Amphipoda) are found in all types of permanent standing and slow flowing water. They are laterally flattened. Some may reach over a cm long.

Tadpole Shrimp (Notostraca) look like frog tadpoles hence their common name. They are relatively uncommon inhabitants of very temporary ponds. They can reach 2 to 3 cm long in some habitats.

Opossum Shrimp (Mysida) are found in some cold, deep lakes of northern Saskatchewan.

Fairy shrimp (Anostraca) are most often found in temporary ponds where they can become numerous in mid-spring. They are usually less than 2 cm long.

Seed Shrimp (Ostracoda) are common in ponds and quiter areas of lakes. They resemble swimming seeds a couple of mm long. Closer inspection will reveal a clam-like shell.

Clam Shrimp (Diplostraca) can be at times common in shallow ponds and lakes. They first appear to be like small swimming clams. Length is about 1.5 cm or less.

Waterfleas (Cladocera) can become so abundant in ponds they form reddish clouds in the water many meters wide and long. They swim with a jerky motion using their antennae. They rarely get larger than a couple of mm.

Water Mites (Hydrachnidiae & Stygothrombiae) are often seen clumsily swimming or crawling amongst the water vegetation and debris. They have eight legs as adults and many are bright red in colour. Most are tiny, the largest only reaching about 2 mm in diameter. They are parasitic on other aquatic insects and can be seen attached to the insect's bodies where they suck body fluids.

Aquatic Insects

Springtails (Collembola) are tiny (1-2 mm long). Most have a forked abdominal appendage or which acts as a spring. This group is found in wet soils and on the water surface of all types of aquatic habitats. They prefer calmer conditions so they do not get trapped in the surface film. They can be seen hopping like fleas on the water. Often on warm spring days they can be seen on the snow surface. Hence their other common name "snowfleas".

Mayflies (Ephemeroptera) are found in most clean waters but their diversity is highest in cooler streams and rivers. The immature stages (larvae) all have gills along the body (abdomen). Adults have two large forewings and two tails.

Stonefly (Plecoptera) larvae are usually found in cool streams and rivers. Size can range from 5 mm to over 5 cm.

Dragonflies and Damselflies (Odonata) are easily recognised as adults. Larval damselflies have three leaf like "gills" at the end of the body while the dragonfly larvae have a cone shaped end.

Aquatic Bugs (Hemiptera) have in common a leathery fore wing and mouthparts shaped into a sucking beak. Water striders (Gerridae) are common in quiet areas of rivers, lakes and ponds where they can be seen walking on the water surface. Water boatman (Corixidae) are common in most water types. They range in size from 3 mm to about one cm. Backswimmers (Notonectidae) are usually not as common but by no means rare. They are about one cm long and have a distinctive keeled back and swim upside down. The giant water bug is the largest aquatic insect found in the province. Adults can reach 8 cm long.

Caddisflies (Trichoptera) larvae have a well-developed head, three pairs of legs and a soft segmented body. Many caddisfly groups build cases, "houses", out of sand grains or pieces of plant material that they drag around with them. Adults resemble moths but lack the coiled mouthparts that moths have. The adult wings are also covered by hairs rather than scales. The

Aquatic Moths (Lepidoptera) look like other moths in the adult stage. As larvae they live in water usually associated with plants. Some create small "houses" out of plant material. And some have bodies covered in gills.

Spongilla flies (Neuroptera) are associated with freshwater sponges, which the larvae feed on. The larvae are only a few of mm long at most and have needle like mouthparts to suck the contents out of sponge cells. The adults have four wings and are also small.

Alderflies (Megaloptera) usually are not very common. The larvae look like some beetle larvae with gills along the sides of the body and a terminal filament at the end of the body. The adults are dark and have very thick wing veins on their four wings.

Aquatic Wasps (Hymenoptera) are parasitic on other aquatic insects. They are usually only seen as adults. Since most look like tiny terrestrial wasps they have to be collected in traps in the water to ensure they are aquatic.

Aquatic Beetles (Coleoptera) come in variety of shapes as larvae but as adults all have the forewings hardened into coverings called elytra. They can be found in all types of aquatic habitats from the most ephemeral pools to the margins of lakes and rivers.

Aquatic Flies (Diptera) adults all have only one pair of wings. The back wings are modified into balancing structures called "halteres". All the biting flies such as mosquitoes, blackflies, horseflies, deerflies and no-see-ums belong to this group. The larvae have no true jointed legs and are tube-shaped with many different body types based on this design. The larvae can be found in all types of aquatic habitats. Some are specially adapted for life in grossly organic polluted situations ie pit toilets. Others require more pristine conditions.