Backswimmer
( Notonectidae )


2012-1023-38CP1309-HET00607-Notonectidae[1330h00s,L,A,dorsum]{EStrand}1-G.jpg

PHOTO COMMENT
Backswimmers live their lives upside down, just under the water surface of freshwater ponds and streams. They have hairs on their body undersides which trap air and they can stay submerged a long time. These are predators of small aquatic animals. Prey is seized with the insect?s forelegs, and, like in many predatory true bugs, a beak is inserted and tissue is liquefied and consumed. Backswimmers, along with Water Boatmen sometimes fly to and take up residence in swimming pools, where they may bite swimmers.

IDENTIFICATION
Identification:Notonectidae
(Latreille, 1802)
Common Name:Backswimmer
Life Stage:(A) adult

PHYLOGENY

Phylum:Arthropoda
Class:Insecta
Superorder:Paraneoptera
Order:Heteroptera
Suborder:Heteroptera
Family:Notonectidae
Taxon Code:HET00607
ITIS/TSN:103557

LOCATION DETAILS
Location Name
Golden Gate Park, Golden Gate Park, San Francisco
County:San Francisco County
ECI Site#:CA38CP0000

RECOGNITION
Description
Backswimmers are aquatic bugs that often swim upside-down. When resting at the surface, body is typically tilted with the head downward. Hind legs are long, with long hairs and are adapted for swimming. Legs: Front legs are raptorial. Front and middle legs are shortened and possess claws. Hind legs are oar-like, much longer, but lack claws. Eyes: Eyes comprise most of the head; ocelli are absent. Antennae: Present but inconspicuous. Mouthparts: piercing/sucking.
Body Length
5-16 mm
Similar Taxa
Water Boatmen (family Corixidae). Backswimmers are similar to the Corixidae in overall form. They may be distinguished by their strongly convex dorsal surface which lacks the thin transverse dark stripes and by the form of the foretarsi which are not scoop-like.

BIOLOGY
Backswimmers are aquatic predators which are frequently encountered. They are unusual in that they swim upside down. Air gill: 3 longitudinal rows of hair-like structures on ventral surface of the abdomen trap air (mostly nitrogen) at the water surface. As oxygen in the bubble is used, more oxygen from the water diffuses into the bubble. When the nitrogen bubble is depleted the insect resurfaces to acquire more. Backswimmers adults fly well and may disperse to new aquatic areas (including swimming pools) in swarms at night. Water Striders are common. Like many aquatic insects they have air gills - a mechanical gill that traps surface air and filters in oxygen more quickly than CO2 diffuses out. However, water striders may stay submerged up to 6 hours.
Food
Predaceous on other insects, aquatic amphibians including frogs and tadpoles, crustaceans and small fish. Hair-like structures on Backswimmer legs detect water movements caused by prey. Forelegs grasp prey and the rostrum (beak) is inserted. Enzymes are injected that kill prey and liquefy internal structures which are consumed.
Habitat
Ponds, freshwater pools, slow flowing streams. May occur in swimming pools.
Importance
Backswimmers are important as predators in aquatic ecosystems and have some importance as control for mosquitoes, feeding on the larvae.
Range
Throughout North America.
Importance
Backswimmers are important as predators in aquatic ecosystems and have some importance as control for mosquitoes, feeding on the larvae.
Development
Males have a stridulatory apparatus probably used to attract females and communicate during courtship. Elongate, white eggs are cemented to underwater plant stems and hatch in a few weeks; first-generation adults appear in July; often 2 generations a year.

CREDITS
Photographer
Erica Strand

References
BugGuide .
ITIS ITIS TSN#.
Powell & Hogue, California Insects. University of California Press.


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