Saskatchewan Aquatic Bugs (Hemiptera)

Giant water bug

There are 15 families and 412 species of aquatic and semi-aquatic Heteroptera reported from North America. The ten families reported from Saskatchewan are represented by about 86 species.

The immature stages and adults are very similar in structure except for the presence of wings in the adult. However, some adult forms of the families Gerridae and Vellidae may be wingless.

Most members of the common family, Corixidae, feed on plant material. Other families are primarily predatory on aquatic insects and invertebrates. Some of the larger species such as the "giant water bug", Lethocerus americanus, will feed on small fish and tadpoles. The forelegs in this creature are used to grasp the prey and the beak injects digestive juices to kill the prey. The internal tissues of the prey are liquified by the digestive juices and sucked out.

The life cycle of most water bugs involve over-wintering adults. Eggs are laid in the early spring and the larvae develop through the summer months. Some, however, have over-wintering eggs.

Giant water bugs, Lethocerus americanus, with their large pincer-like forelegs and beak can give an unwelcome bite to people attempting to handle them. The much smaller Notonectidae often migrate in numbers into outdoor swimming pools where they can also inflict a nasty bite if picked up by unsuspecting people. Other than such interactions most people are not aware of these aquatic insects. However, in the early fall vast numbers of water boatmen (Corixidae) and also giant water bugs migrate from the smaller ponds in SK to larger ponds, lakes and rivers to overwinter. During migration they are readily attracted to lights and shining surfaces. People regularly make comments on the small banks of dead and dieing water boatmen found under lights. A similar more diffused migration from the permanent overwintering waters to smaller ponds occurs in the spring.

A number of hemipteran families, Gerridae, Microvellidae and Mesovellidae are able to walk on the water surface due to hydrofuge hairs on their legs that prevent them from breaking through the surface tension, hence the common name of "water striders".

Below is a basic taxonomic key to the families of true bugs found in SK modified from Brooks and Kelton (1967).

1a: Antennae shorter than head. Go to 2

1b: Antennae longer than head.--Go to 6

2a: Beak (mouthparts) triangular. Last segment (pala) of forelegs in the form of a scoop.--Corixidae (Water Boatman)

2b: Beak in the form of a relatively long cylinder of three or four segments. Forelegs not scoop-like.--3

3a: Body thin and long, adults greater than 35 mm. Abdomen with two long siphons (breathing tubes) at the end. Forelegs designed for grasping.-- Nepidae (Water Scorpions) (Arrows indicate grasping forelegs and long siphons.)

3b: Body not as above. If thin and long lacks the long terminal siphons and forelegs not designed for grasping.--4

4a: Usually large, greater than 30 mm as adults. Body flattened in appearance. Foreleg with a single claw.-- Belostomatidae (Giant Water Bugs)

4b: Much smaller. Foreleg has two claws.--5

5a: About 2 to 3 mm long. Extremely convex dorsally. Hind legs are weak. Found crawling through the vegetation. Poor swimmers.-- Pleidae (Pygmy Backswimmers)

5b: Adults larger, usually about 4 or more mm long. Hind legs used as oars for swimming. Usually seen swimming in strong jerky movements on their backs.-- Notonectidae (Backswimmers)

6a: Four to five wing membrane veins forming definite cells. Seen around the edges of aquatic habitats.-- Saldidae (Shore Bugs)

6b: Wings without distinct veins or cells.--7

7a: Tarsal claws not at apex of segment.--8

7b: Tarsal claws at apex of tarsal segment.--9

8a: Hind femur much longer than abdomen.-- Gerridae (Water Striders)

8b: Hind femur shorter than abdomen.-- Veliidae (Small Water Striders)

9a: Eyes set far back from front of head. Head about as long as thorax. Body is relatively long compared to its width. Cylindrical. (Arrows indicate eyes and beak.)-- Hydrometridae (Marsh Treaders)

9b: Head much shorter. Eyes are near the posterior of head. Body more robust.--10

10a: About 2 mm long. Tarsus two segmented. Body has numerous tightly compact, short hairs.--Hebridae (Velvet Water Bugs)

10b: Larger, about 3 or 4 mm long. Tarsus with three segments. Body without "carpet" of short hairs.--Mesoveliidae

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References:

Brooks A. R. and L. A. Kelton. 1967. Aquatic and semiaquatic Heteroptera of Alberta, Saskatchewan, and Manitoba (Hemiptera). Mem. Entomol. Soc. Canada 51: 1-92

Mau, H.E.L., R.G. Foottit, K.G.A. Hamilton and G.G.E. Scudder. 2000. Checklist of the Hemiptera of Canada and Alaska. NRC Research Press, Ottawa, ON.

Parker, D. and I. Phillips. 2007. Collection records of three aquatic bugs (Heteroptera); pygmy backswimmer (Pleidae), water scorpion (Nepidae) and marsh treader (Hydrometridae) for Saskatchewan, Canada. Blue Jay. 65:143-148.

Polhemus, J.T. 2008. Chapter 15: Aquatic and semiaquatic Hemiptera. In. Merritt, R.W., K.W. Cummins, and M.B. Berg. An introduction to the aquatic insects of North America. Fourth Edition. Kendall/Hunt Publ. Co. Dubuque, Iowa.

Scudder G.G.E. 1987. Aquatic and semiaquatic Hemiptera of Peatlands and marshes in Canada. Mem. Ent. Soc. Canada 140:65-98.