Numbers
Nomina Insecta Neartica lists 17 North American genera and over 100 species. This is the largest family of water bugs.
Identification
Body elongate and oval, dorsal surface flattened, with narrow dark crosslines. Front legs short, tarsi 1-segmented and scoop-shaped. Hind legs elongate, with fine hairs, functioning as oars.
(1)
The species are all very simlar and can be distinguished mainly by structures of the male genitalia and other technical characteristics.
(2)
Critical Diagnostic Characters Used in Corixid Identification (to genus)
Corixidae are among the largest and most diverse aquatic bug groups in North America. Identifying corixids can be a daunting task as members of even different genera can be superficially similar to the layman. However genus-level identification is possible from images if good shots of the following appropriate regions of the insect are taken:
1) Both dorsal and ventral shots of the whole insect. Preferably for identification purposes, the insects should be photographed dry so that technical features on the body surface are not obscured by the water. Some important features seen in these views include the colour pattern of the pronotum and hemielytra, surface texture of the hemielytra, and a few technical features on the underside.
2) Lateral view of the insect. The key diagnostic traits here are the nodal furrow as pictured here
, and translucent areas (pruinose areas) on the claval suture and the area immediately posterior to the nodal furrow.
3) Facial shot showing details of the rostrum
4) Shot of the upper ventral half of the insect (showing prothoracic lobes, mesepimeron, and scent glands.
5) Shot of the dorsal abdominal segments (tergites)- sex determination often relies on examination of the dorsal terminal segments; males generally have asymmetrical dorsal terminalia and may or may not have a black spot-like structure called a "strigil" depending on genus; females have symmetrical terminalia.
6) Palae, especially of the male- of some importance in genus identification but generally more critical in species ID.
Size data is also important for some aspects of corixid identification and should preferably be included as some genera do have a specific size range.
Keys to genera can be found in Merritt and Cummin's "Introduction to Aquatic Insects of North America" as well as online in both "Aquatic Insects of Michigan" and " Aquatic Invertebrates of Alberta". If one is eager to go further with a species ID, Hungerford's publication on Western Hemisphere Corixidae (1948 publication, 1977 reprint) is an excellent resource to consult for species keys. Species identification requires more technical examination of specific features such as genitalia, male palae (front tarsi), ventral structures, and others. For some genera, species identification may be possible from photos but for others, especially for large genera (eg Sigara. Hesperocorixa), picture-based ID is not always possible.
Habitat
Common in ponds. Also found in birdbaths. A few species live in streams, and others are found in brackish pools along the seashore above the high tidemark.
Food
Algae and minute aquatic organisms.
Life Cycle
Oval eggs are cemented to underwater supports, sometimes forming a dense crust. They hatch in 7-15 days.
(3)Remarks
Males make sounds by rubbing their front legs against the front of their head.
Unlike
Backswimmers, Water Boatmen do NOT bite.
Occasionally adults will fly to artificial light.
See Also
Water Boatmen are similar in appearance to
Backswimmers. However, Water Boatmen swim dorsal side up, while Backswimmers swim upside-down.
Print References
"Peterson's Field Guide to Insects", page 112-113
(1)
"National Audubon Society Field Guide to North American Insects & Spiders",page 460, plate 100
(3)
"American Insects: A Handbook of the Insects of America North of Mexico"
(2), p. 281
Internet References
Cedar Creek Insect Photo Album - has photos and info on many Water Boatman species
Duluth Stream's website - has a photo and general information
Texas A&M University - has detailed info and photos of Water Boatmen
