Water boatman (Notonecta glauca)

Water boatman on aquatic vegetation
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Water boatman fact file

Water boatman description

GenusNotonecta (1)

The water boatman is a common water bug, which swims on its back and is often seen at the surface of the water (3). It is light brown in colour with a number of dark markings and large reddish eyes (2). The powerful oar-like hind legs are modified for swimming; they are long, flattened and fringed with hairs (3). The forelegs, which are short and strong, are used for grabbing prey (2). The larvae, or 'nymphs', are white or greenish in colour and are fairly similar in appearance to the adults (2). The water boatman often looks silvery as air becomes trapped in a layer of bristles covering the lower surface (4). All true bugs have sucking mouthparts known as a rostrum or a beak; in this species the rostrum is very short and strong (3).

Also known as
Length: 14-17 mm (2)

Water boatman biology

The water boatman is a highly effective predator; it tends to stay motionless at the surface until it detects movements in the water, it then swims towards the source of the movement, and hunts by sight when it is close to its prey. This bug has toxic saliva and can inflict a very painful bite. A wide range of aquatic prey is taken, and they can tackle items as large as tadpoles and small fish (3).

Although mating may take place from December to late May, females typically lay their eggs between early February and early May. The eggs are embedded in plant stems. Bugs undergo a type of development known as incomplete metamorphosis in which the larvae undergo a series of moults. The stages between moults are known as 'instars'; there are 5 instars in this species, and it takes 2 months for water boatman larvae to become adults (3).


Water boatman range

Widely distributed and common throughout Britain (1).

You can view distribution information for this species at the National Biodiversity Network Atlas.

Water boatman habitat

Found in still and flowing waters with aquatic plants (1), including ponds, lakes and rivers (2).


Water boatman status

Widespread and often common (3).


Water boatman threats

Not threatened at present.


Water boatman conservation

Conservation action has not been targeted at this species.

There may be further information about this species available via the National Biodiversity Network Atlas.

Find out more

For more on invertebrates and their conservation see Buglife, the Invertebrate Conservation Trust at:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk


Incomplete metamorphosis
Type of insect development (also known as hemimetabolous development) in which the adult form is reached via a series of moults. The larva (nymph) resembles a miniature wingless adult; the wings develop externally as the nymph grows.
Stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.


  1. National Biodiversity Network Species Dictionary (Jan 2003): http://www.nhm.ac.uk/nbn/
  2. Olsen, L., Sunesen, J., & Pedersen, B. V. (1999) Small freshwater creatures. Oxford University Press, Oxford.
  3. Southwood, T. R. E. & Leston, D. (1959) Land and water bugs of the British Isles. Frederick Warne & Co. Ltd., London.
  4. Sterry, P. (1997) Complete British Wildlife photo guide. Harper Collins Publishers, London.

Image credit

Water boatman on aquatic vegetation  
Water boatman on aquatic vegetation

© Peter Clarke/SAL / gettyimages.com

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