|
Family Dytiscidae - Predacious Diving Beetles
Classification Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Class Insecta (Insects)
Order Coleoptera (Beetles)
Suborder Adephaga (Ground and Water Beetles)
Family Dytiscidae (Predacious Diving Beetles)
Numbers White, p. 97, lists 41 genera, 476 species (1)Size body length 1.2-40 mm Identification Aquatic beetles whose hind tibiae have long hairs, other modifications for swimming. Dytiscids move their legs together like oars, in the manner of Backswimmers in the Hemiptera. In other aquatic beetle families, such as the Hydrophilidae, the legs are moved alternately. (2)
In much of the eastern United States, the only two very large (25-35 mm) members of this family are Dytiscus and Cybister. They are similar, but several characters can be used to separate them. (3) (4)
- Lower/outer hind tibial spur much wider than upper/inner in Cybister, spurs similar in size in Dytiscus.
- Metatibia of Cybister is short and broad, that of Dytiscus is longer and narrower.
- Prosternum of Cybister is greenish, that of Dytiscus is reddish.
- Structure of adhesive pads on male protarsi differs between the two genera. Dytiscus has two larger circular disks on with adjacent smaller ones. Cybister has a longer, broader pad. This is shown nicely in figure 33 of White. (1)
- On metatarsi, outer margin of Cybister has a narrow fringe, lacking in Dytiscus.
- Females of Cybister have long lengthwise scratches on elytra, lacking deep furrows found on some female Dytiscus.
- Male Dytiscus tends to have prominent rows of punctures on elytra, weak in Cybister.
Range Much of North America. Print References Papp, pp. 60-62, discusses locomotion, has good discussion of family characters, including those of larvae (2).
Ciegler, pp. 41-89, extensive keys (4)
America Beetles, Vol. 1, Chapter 12 (5)
Castner, pp. 112-113, has representative photos, comparing with other aquatics. (6)
Arnett et al. pp. 108-114 (7)
D.J. Larson, Y. Alarie, and R.E. Roughley, Predaceous Diving Beetles (Coleoptera: Dytiscidae) of the Nearctic Region, with emphasis on the fauna of Canada and Alaska(8) keys to all species, with descriptions and distribution maps for those found in Canada (which covers many also found in the lower 48 US) Internet References preserved adult images of 46 species with descriptions, distribution, habitat, and biology of each (Charles Staines, Discover Life in America, dlia.org)
Identification manual for the water beetles of Florida (Coleoptera: Dryopidae, Dytiscidae, Elmidae, Gyrinidae, Haliplidae, Hydraenidae, Hydrophilidae, Noteridae, Psephenidae, Ptilodactylidae, Scirtidae) by John H. Epler, Ph.D.
Aquatic Invertebrates of Alberta - Beetles General info, keys to familes and genera, and several dozen photos Works Cited | 7. | How to Know the Beetles
By Ross H. Arnett, N. M. Downie, H. E. Jaques | |
|
|
|
|
