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Subfamily Dytiscinae

Acilius mediatus? - Acilius fraternus Large diving beetle - Dytiscus verticalis - female Predacious Diving Beetle larva - Dytiscus Predaceous Diving Beetle - Dytiscus alaskanus - female Dytiscid - Dytiscus circumcinctus - male Giant Green Water Beetle - Dytiscus marginicollis - male Predaceous Diving Beetle - Acilius mediatus - female Predaceous Diving Beetle - Prodaticus bimarginatus
Classification
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
Size
8-40 mm (Nearctic species)
Identification
Adults:
generally medium to very large sized beetles
Eyes unnotched at antennal bases
there is a visible scutellum
males with protarsal segments 1-3 modified to form a large, broad oval palette, often with variable number of suckers on the ventral surface-these are used to grasp the female during mating.
Larvae:
Anterior margin of the clypeus (frontoclypeus) is rounded
anteroventral margin of femur and tibia with a fringe of swimming hairs
both abdominal segments 7 and 8 fringed laterally with swimming hairs
generally large sized
In much of the e. US, the only two very large (25-35 mm) members of the family are Dytiscus and Cybister which can be separated as follows:(1)(2)
Lower/outer hind tibial spur much wider than upper/inner in Cybister, similar in size in Dytiscus
Metatibia in Cybister is short and broad, in Dytiscus, longer and narrower
Prosternum greenish in Cybister, reddish in Dytiscus
Adhesive pads on male protarsi in Dytiscus with two larger circular disks on with adjacent smaller ones; in Cybister, the pad is longer and broader
Metatarsi in Cybister with a narrow fringe on the outer margin, lacking in Dytiscus
Females of Cybister have long lengthwise scratches on elytra, lacking deep furrows found on some female Dytiscus
Male Dytiscus tend to have prominent rows of punctures on elytra, weak in Cybister
Works Cited
1.A Manual of Common Beetles of Eastern North America
Dillon, Elizabeth S., and Dillon, Lawrence. 1961. Row, Peterson, and Company.
2.Water Beetles of South Carolina
Janet Ciegler. 2003. Clemson University.