Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
Clickable Guide
Moths Butterflies Flies Caterpillars Flies Dragonflies Flies Mantids Cockroaches Bees and Wasps Walkingsticks Earwigs Ants Termites Hoppers and Kin Hoppers and Kin Beetles True Bugs Fleas Grasshoppers and Kin Ticks Spiders Scorpions Centipedes Millipedes

Upcoming Events

Interested in a 2022 BugGuide gathering in New Mexico?

Photos of insects and people from the Spring 2021 gathering in Louisiana, April 28-May 2

National Moth Week 2020 photos of insects and people.

Photos of insects and people from the 2019 gathering in Louisiana, July 25-27

Discussion, insects and people from the 2018 gathering in Virginia, July 27-29

Photos of insects and people from the 2015 gathering in Wisconsin, July 10-12

Photos of insects and people from the 2014 gathering in Virginia, June 4-7.

Previous events


Genus Acilius

Diving Beetle - Acilius fraternus Dytiscidae 01a - Acilius abbreviatus - male - female Dytiscid - Acilius semisulcatus Predaceous Diving Beetle - Acilius mediatus - male Acilius semisulcatus Predaceous Diving Beetle - Acilius semisulcatus? - Acilius Acilius mediatus water beetle - Acilius mediatus
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.