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Genus Acilius

ribbed-elytra water beetle - Acilius semisulcatus - female Water beetle larva? - Acilius Acilius mediatus? - Acilius mediatus - male Predaceous diving beetle - Acilius mediatus Dytiscus sp? - Acilius Diving Beetle - Acilius Acilius mediatus Acilius - male - female
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Coleoptera (Beetles)
Suborder Adephaga (Ground and Water Beetles)
Family Dytiscidae (Predaceous Diving Beetles)
Subfamily Dytiscinae
Tribe Aciliini
Genus Acilius
Explanation of Names
Author: Leach (1817)
ca. 6 Nearctic spp.(1)
adult 10-16 mm, larva 15-30 mm
Adult: top of head yellowish with two dark transverse bands, the anterior band undulate or shaped like an M or upside-down W; pronotum yellowish with two dark transverse bands on disc, not terminally, as in Graphoderus; notched spur on hind tibia; elytral mottling or speckling less pronounced than in Graphoderus; elytra punctate (and longitudinally sulcate in female)
Larva: swimming hairs present on last two abdominal segments; ligula (structure located between the maxillary palps) is deeply bifid (2-pronged).
Holarctic; throughout NA (including the arctic)(1)
submergent vegetation
Year-round with adults most frequently encountered in spring during mating season and late summer when they disperse to overwintering sites
Life Cycle
Adults have been reported to overwinter in permanent water bodies and disperse to breeding sites during spring; larvae complete development later in the spring and into the early summer; newly emerged adults disperse to overwintering sites later in the summer and into the fall(2)
See Also
Graphoderus elytra more heavily mottled or speckled, and dark transverse bands located terminally on pronotum
Internet References
photos and species accounts of A. fraternus and A. mediatus (Charles Staines)
Works Cited
1.American Beetles, Volume I: Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia
Arnett, R.H., Jr., and M. C. Thomas. (eds.). 2000. CRC Press LLC, Boca Raton, FL.
2.Predaceous Diving Beetles (Coleoptera: Dytiscidae) of the Nearctic Region, with emphasis on the fauna of Canada and Alaska
D.J. Larson, Y. Alarie, and R.E. Roughley. 2001. NRC 43253.