All the insects belonging to this tribe are either water insects, or
found only in the immediate neighbourhood of water. It contains the
remaining families of the _Heteroptera_, six in number.
_Family 10, Saldidæ._--The majority of species belonging to this
family are small, dull-coloured insects, always found in the
neighbourhood, though they are not strictly aquatic.
_Family 11, Hydrometridæ._--The habits of most of these insects are
herbivorous, and they are all found near water.
_Hydrometra stagnorum_ is a black or brown insect, more or less tinged
with reddish, and about half an inch long. It is found running on the
surface of water, or else on the banks or among water plants, but is
not so active as some of the other species.
[Illustration: Fig. 91.--Halobates Pictus (Mag.)]
_Family 12, Gerridæ._--This family includes some very familiar insects,
which may be seen running over the surface of every piece of water.
These insects, of which several species are abundant in Britain, have
boat-shaped bodies. The typical form is _Gerris lacustris_, which may
be met with almost anywhere. They are predaceous in their habits,
feeding upon other insects. Some nearly allied, but mostly very small
species, with legs even longer in proportion than those of our common
forms, are met with at sea within the tropics, and often at a great
distance from land.
[Illustration: Fig. 92.--Galgulus Oculatus (Mag.)]
_Family 13, Galgulidæ._--This family only includes a few American
species, which are generally brown spotted with yellow. _Galgulus
oculatus_ inhabits the southern part of the United States, and measures
about two-fifths of an inch in length.
_Family 14, Nepidæ._--The species of this family are not very numerous,
but are of considerable interest. They are of large size, and very
fierce and voracious. The genus _Betostoma_, found in the East Indies
and America, includes the largest species of _Heteroptera_, some of
which measure four and a half inches in length, and nearly six inches
in expanse of the wing. Their food consists of small fish, frogs, etc.
[Illustration: Fig. 93.--Nepa Cinerea.]
The best-known species in our own country is the Water Scorpion (_Nepa
cinerea_), which has the power of inflicting a very painful wound
if handled. It measures about an inch in length. In colour it is
yellowish-grey, the back of the abdomen being red, and its large front
legs, which somewhat resemble the claws of a scorpion, have given
rise to the name by which it is popularly known. It is very common in
stagnant water.
[Illustration: Fig. 94.--Notonecta Glauca.]
[Illustration: Fig. 95.--Metacanthus Punctipe (Mag.)]
_Family 15, Notonectidæ._--These insects are commonly known as "Water
Boatmen," from their habit of rowing themselves about on their backs
with their long hind legs. They are carnivorous, feeding on small
insects and other "fry."
The most typical British species is _Notonecta glauca_, a yellowish
insect about half an inch long. It is a most predaceous insect, and can
bite severely.
Another common species inhabiting our own country is _Coriax
Geoffroyi_, which is nearly half an inch long. The _Notonectidæ_ are
all very powerful and active creatures.
[Illustration: Fig. 96.--Corisa Striata.]