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 Major Groups | Insecta (insects) | Hemiptera (bugs) | Notonectidae


Major Group: Insecta

Descriptive Features:

  • body strongly convex dorsally, flattened ventrally and tapered caudally, nymphs often with a very light-coloured back
  • eyes large, reniform and occupy most of the head
  • ocelli absent
  • antennae short, 2 to 4-segmented, not visible from above, housed beneath the eye
  • rostrum short, stout and 4-segmented
  • pronotum subtrapezoidal
  • scutellum large and triangular
  • fore- and midlegs adapted for grasping
  • hindlegs adapted for swimming, long, flattened, oar-like and densely fringed with hair
  • tarsi usually 2-segmented, although males of Anisops have 1-segmented foretarsi, pretarsi with 2 claws, greatly reduced in the hindlegs
  • ventral surface of abdomen with a prominent, median, hairy keel, and reflexed, hair-fringed lateral margins, which form 2 longitudinal channels that function as air chambers
  • Total length: 4.0 - 11.5 mm 
    • Taxonomic Checklist: Genera

      Distribution: Australia wide

      Sensitivity Rating: SIGNAL grade 1

      Functional Feeding Group: predators

      Ecology: Instream habitat: Notonectid bugs occur in all habitats of still and slow flowing water bodies however some species seem to prefer waters with moderate to rich macrophyte growth.
      Feeding ecology: These bugs are voracious predators that will accept any suitable prey but typically feed on a mixture of invertebrates, in particular mosquito larvae, tadpoles and small fish from open water and the water surface, even their own young. Prey is grasped with modified fore- and midlegs. Predatory strategies differ among genera; for example, Enithares and Notonecta hang at the surface with the hind legs held forward ready to dart after approaching prey in or on the water surface film, whereas Anisops hovers in midwater. Some Notonectidae species can inflict a painful stab on humans.
      Habit: Commonly known as ‘backswimmers’ due to their behaviour of swimming upside down, notonectid bugs are excellent swimmers that also fly easily and can therefore colonise new ponds and wetlands quickly. They are dependant on atmospheric air for respiration and so are usually found near the water surface. Replenishable air bubbles are carried on the underside of their abdomen in two troughs lined with hydrofugal hairs. Some Notonectidae species, such as Anisops, have a blood pigment similar to humans, which is very efficient at carrying oxygen. They can therefore carry smaller bubbles than other bugs and remain neutrally buoyant. This allows them to hang in midwater, without sinking or constantly returning to the surface. The back of some notonectid bugs is light coloured so that the animal is not conspicuous from below, against the light of the sky.
      Life history: Males can produce sounds to attract females. Eggs are often deposited into water plants. In Northern Hemisphere species, eggs are laid in or on aquatic plants, but those of Notonecta are often found on the surface of rocks and submerged debris. There are five nymphal instars.



      notonectid bug with parasitic mite

      Information Sources: Andersen & Weir 2004, Cassis & Gross 1995, Lansbury & Lake 2002, Gooderham & Tsyrlin 2002, Ingram et al 1997, Davis & Christidis 1997
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