(Order Coleoptera; Family Gyrinidae)
Dineutus assimilis (Photo by Zachary Quick)
(Kansas: Sedgwick County. WSU Ninnescah Reserve, 5.1 mi NW Viola, 37°32'24"N, -97°40'47"W. At the banks of the Ninnescah River. Septermber 8, 2011)
Adult Diagnosis: This is a common aquatic, black beetle that is approximately 0.9 cm (.375 inches). The body is flat, exhibiting a metallic-bronze appearance on the upper surface. The most posterior body segment is rounded and depressed on the lower surface. The antennae are short. Flattened legs permit fast-paced mobility in aquatic environments. Sexes share a similar morphology; however the female has slightly extended elytra.
Natural History: Adult whirligig beetles inhabit the upper surface of bodies of water; their most notable feature is the division of their compound eyes which enables them to view both above and below the surface. Another adaptation is a foul smelling, pygidial gland secretion called gyrinidal that acts as a chemical irritant towards predators. Additionally, their antennae are used to produce a form of echolocation by sensing waves colliding and bouncing off the surface of objects in their path.
Males and females form non-mating, gregarious communities during the day in late summer and fall. Community assemblage, which utilizes sexual segregation, is most notably employed as a means to avoid predation. Upon disturbance, females have been observed to migrate towards the center of the group while males occupy the outer perimeter; this lasts several minutes. When there is no detectable threat, segregation is determined based on hunger. Less nourished individuals tend to stray towards the outer region of the group where food is more easily accessible.
Diapause during the winter is followed by laying eggs in the spring. Eggs are laid in groups of 7 to 40 on underwater plants. The larvae that hatch remain beneath the water until the middle of summer at which point the larvae climb above the surface and form mud cocoons on plants. Upon completion of metamorphosis at the end of the summer, the adult Dineutus returns to the water.
Adult Dineutus typically do not spend their lifetime in the same residence. Migration between nearby ponds and streams is common. Some individuals observed have flown up to 20 km to reach a new location.
(Left) Dineutus assimilis divided compound eye (from: http://insectzoo.msstate.edu/OrkinZoo/pond.html). (Right) Dineutus assimilis displaying group assemblage behavior (copyright by Ted C. McCrae: http://beetlesinthebush.wordpress.com/2011/01/16/calm-waters-frenzied-beetles/).
Distribution: While specifics regarding the geographical range of Dineutus are not documented, members of the family Gyrinidae commonly inhabit ponds and slow moving water throughout many regions of Kansas and North America.
Distribution Gyrinidae in North America (Habitat Range=Gray) (from: http://bugguide.net/node/view/95/data).
Habitat: Adults and larvae are found inhabiting ponds, streams, and other still or slow-moving bodies of water. While adults are often found at the surface of the water, they are capable of respiration while submerged by enclosing an air bubble beneath their elytron.
Oxygen bubble used for respiration (from: http://www.biodiversitysnapshots.net.au/BDRS/public/speciesInfo.htm?spid=717&mode=fieldguide).
Diet: Adults have modified forelegs and mouthparts adapted for predation. Consumption of small insects at the surface of the water as well as scavenging for food particles is common behavior. Larvae feed on small aquatic insects.
Gyrinidae mouthparts (from: http://www.bumblebee.org/invertebrates/ColeopteraA.htm).
Gyrinidae larvae (from: http://www.bumblebee.org/invertebrates/ColeopteraA.htm).
Conservation Status: Stable
Flash Expansion of Whirligig Beetles
Whiligig Beetles w/music
Beneficial Bugs of North America- Whirligig Beetles: http://beneficialbugs.org/bugs/Whirligig_Beetle/Whirligig.htm
Gullan, P. J. and P. S. Cranston. 2010. The Insects: An Outline of Entomology, 4th Edition. Wiley-Blackwell, Hoboken, NJ. 565 pp.
Nurnberger, Beate and Richard G. Harrison. 1995. “Spatial Population Structure in the Whirligig Beetle Dineutus assimilis: Evolutionary Inferences Based on Mitochondrial DNA and Field Data.” Evolution 49(2): 266-275.
Romey, William L. and Abigail C. Wallace. 2007. “Sex and the selfish herd: sexual segregation within nonmating whirligig groups.” Behavioral Ecology. 18(5): 910-915.
Salsbury, Glenn A. and Stephan C. White. 2000. Insects in Kansas, 3rd Edition. Kansas Department of Agriculture, Topeka, KS.
Submitted By: Zachary Quick, November 2011