Bug FAQGrousewinged Backswimmer
Notonecta undulata · Order: Hemiptera · Family: Notonectidae
The grousewinged backswimmer is a small aquatic bug about 10 to 12 mm long with four-segmented antennae. It lives in slow-moving ponds and lakes across parts of western North America, especially southern Canada and the western United States. It is a generalist predator that especially targets mosquito larvae.
Source: Wikipedia
How to recognize it
Notonecta undulata can be told apart from other backswimmers by its size and its four-segmented antennae.
Source: Wikipedia
Size
Adults measure roughly 10 to 12 mm in length and have antennae made up of four segments.
Source: Wikipedia
Where it lives
They prefer quiet, slow-moving water such as small ponds and lakes, but will also use small streams when needed.
Source: Wikipedia
What it eats
They are generalist predators that eat many aquatic invertebrates and any terrestrial insects that land on the water surface. Mosquito larvae are their preferred prey.
Source: Wikipedia
Life cycle
The species produces two generations per year (bivoltine). Eggs develop through five nymphal stages during spring and summer.
Source: Wikipedia
When you see it
The first generation matures in July and then produces a second generation. All adults overwinter and lay eggs again in early spring.
Source: Wikipedia
Where it comes from
Backswimmers are widespread across North America.
Source: Wikipedia
Lookalikes
They differ from water boatmen (Corixidae) by having a segmented beak and unmodified front legs, whereas water boatmen have highly modified front legs.
Source: Wikipedia
Where it is found in the US
Recorded in 45 of 51 states and DC. Most records: Kansas, Illinois, Colorado, Michigan, Utah, Texas, Kentucky, Minnesota.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Status: native in North America; native in Canada. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
What do grousewinged backswimmers eat?
They are generalist predators that consume many aquatic invertebrates and prefer mosquito larvae.
Source: Wikipedia
Where can I find these bugs?
They live in slow-moving ponds and lakes, and sometimes in small streams, across western North America, especially in southern Canada and the western United States.
Source: Wikipedia
How can I tell them apart from water boatmen?
Backswimmers have a segmented beak and front legs that are not highly modified, unlike water boatmen which have very modified front legs.
Source: Wikipedia
How many generations do they have each year?
They are bivoltine, producing two generations annually, with the first generation maturing in July and the second developing from eggs laid in spring.
Source: Wikipedia
Same family (Notonectidae)
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Notonecta_undulata
Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia
Text written 2026-10-23 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-23.