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<noinclude><pagequality level="3" user="DivermanAU" />{{EB1911 Page Heading|  |HEMIPTERA||259}}</noinclude>
animal tissue from which the insect is sucking. The point of the
rostrum is pressed against the surface to be pierced; then the
stylets come into play and the fluid food is believed to pass into
the mouth by capillary attraction.

{|{{Ts|ma|sm92|lh12|width:420px}}
|-
|colspan=2 {{Ts|ac|mc|ma|pt1}}|[[File:EB1911 Hemiptera - Fig. 2—Head and Prothorax of Cicad, parts separated.jpg|400px]]
|-
|colspan=2 {{Ts|pl.5|vtp|al|sm92}}|After Marlatt, ''Bull. 14'' (N.S.) ''Div. Ent. U.S. Dept. Agr.''
|-
|colspan=2 {{Ts|sm92|lh13|ac|pl1|pr1}}|{{sc|Fig. 2.}}—Head and Prothorax of Cicad, parts separated.
|-
|{{Ts|ar}}|I.,||''a'', frons; ''b'', clypeus; ''c'', labrum; ''d'', epipharynx.
|-
|{{Ts|ar}}|I′.,||Same from behind.
|-
|{{Ts|ar}}|II.,||Mandible.
|-
|{{Ts|ar}}|III.,||1st maxillae, ''a'', base; ''b'', sheath; ''c'', stylet; ''c''&#8202;′, muscle.
|-
|{{Ts|ar|vtp}}|IV., ||2nd maxillae, ''a'', sub-mentum; ''b'', mentum; ''c'', ligula, forming beak;<br>''d'', hypopharynx (shown also from front ''d''&#8202;′, and behind ''d''&#8202;″).
|-
|{{Ts|ar}}|V., ||Prothorax, ''b'', haunch; ''a'', trochanter.
|}

The prothorax (figs. 1 and 2, V.) in Hemiptera is large and
free, and the mesothoracic scutellum is usually extensive. The
number of tarsal segments is reduced; often three, two or only
one may be present instead of the typical insectan number
five. The wings will be described in connexion with the various
sub-orders, but an interesting peculiarity of the Hemiptera
is the occasional presence of winged and wingless races of the
same species. Eleven abdominal segments can be recognized,
at least in the early stages; as the adult condition is reached,
the hinder segments become reduced or modified in connexion
with the external reproductive organs, and show, in some male
Hemiptera, a marked asymmetry. The typical insectan ovipositor
with its three pairs of processes, one pair belonging to the
eighth and two pairs to the ninth abdominal segment, can be
distinguished in the female.

<table {{Ts|ma}}>
<tr><td {{Ts|ac|mc|ma|pt1}}>[[File:EB1911 Hemiptera - Fig. 3.—a, Cast-off nymphal skin of Bed-bug.jpg]]</td></tr>
<tr><td {{Ts|pl.5|pr.5|vtp|al|sm}}>After Marlatt, ''Bull. 4'' (N.S.) ''Div. Ent. U.S. Dept. Agr.''</td></tr>
<tr><td {{Ts|sm92|ac|pl1|pr1}}><poem>{{sc|Fig. 3.}}—''a'', Cast-off nymphal skin of Bed-bug (''Cimex lectularius'');
''b'', Second instar after emergence from ''a''; ''c'', The same after a meal.</poem></td></tr></table>

In the nervous system the concentration of the trunk ganglia
into a single nerve-centre situated in the thorax is remarkable.
The digestive system has a slender gullet, a large crop and no
gizzard; in some Hemiptera the hinder region of the mid-gut
forms a twisted loop with the gullet. Usually there are four
excretory (Malpighian) tubes; but there are only two in the
''Coccidae'' and none in the ''Aphidae''. “Stink glands,” which
secrete a nauseous fluid with a defensive function, are present
in many Hemiptera. In the adult there is a pair of such glands
opening ventrally on the hindmost thoracic segment, or at the
base of the abdomen; but in the young insect the glands are
situated dorsally and open to the exterior on a variable number of
the abdominal terga.

''Development.''—In most Hemiptera the young insect (fig. 3)
resembles its parents except for the absence of wings, and is
active through all stages of its growth. In all Hemiptera the
wing-rudiments develop externally on the nymphal cuticle,
but in some families—the cicads for example—the young insect
(fig. 10) is a larva differing markedly in form from its parent,
and adapted for a different mode of life, while the nymph before
the final moult is sluggish and inactive. In the male ''Coccidae''
(Scale-insects) the nymph (fig. 4) remains passive and takes no
food. The order of the Hemiptera affords, therefore, some
interesting transition stages towards the complete metamorphosis
of the higher insects.

<table {{Ts|bc}} style="float: right; width: 220px;">
<tr><td {{Ts|ac|pl1}}>[[File:EB1911 Hemiptera - Fig. 4.—Passive Nymph or “Pupa” of male scale-insect.jpg]]</td></tr>
<tr><td {{Ts|sm|lh12|al|pl2|pr2|pb1}}>After Riley and Howard, ''Insect Life'', vol. i. (U.S. Dept. Agr.).</td></tr>
<tr><td {{Ts|sm92|lh13|al|pl2|pr1}}>{{sc|Fig. 4.}}—Passive
Nymph or “Pupa” of male scale-insect (''Icerya'').</td></tr></table>

''Distribution and Habits.''—Hemiptera are widely distributed,
and are plentiful in most quarters of the globe, though they
probably have not penetrated as far into remote and inhospitable
regions as have the Coleoptera, Diptera
and Aptera. They feed entirely by
suction, and the majority of the species
pierce plant tissues and suck sap. The
leaves of plants are for the most part the
objects of attack, but many aphids and
scale-insects pierce stems, and some go
underground and feed on roots. The
enormous rate at which aphids multiply
under favourable conditions makes them
of the greatest economic importance,
since the growth of immense numbers of
the same kind of plant in close proximity—as
in ordinary farm-crops—is especially
advantageous to the insects that feed on
them. Several families of bugs are predaceous
in habit, attacking other insects—often
members of their own order—and
sucking their juices. Others are
scavengers feeding on decaying organic
matter; the pond skaters, for example,
live mostly on the juices of dead floating
insects. And some, like the bed-bugs,
are parasites of vertebrate animals, on
whose bodies they live temporarily or permanently, and whose
blood they suck.

The Hemiptera are especially interesting as an order from
the variety of aquatic insects included therein. Some of these—the
''Hydrometridae'' or pond-skaters, for example—move over
the surface-film, on which they are supported by their elongated,
slender legs, the body of the insect being raised clear of the water.
They are covered with short hairs which form a velvet-like pile,
so dense that water cannot penetrate. Consequently when the
insect dives, an air-bubble forms around it, a supply of oxygen is
thus secured for breathing and the water is kept away from the
spiracles. In many of these insects, while most individuals
of the species are wingless, winged specimens are now and then
met with. The occasional development of wings is probably
of service to the species in enabling the insects to reach new
fresh-water breeding-grounds. This family of Hemiptera (the
''Hydrometridae'') and the ''Saldidae'' contain several insects that
are marine, haunting the tidal margin. One genus of ''Hydrometridae''
(''Halobates'') is even oceanic in its habit, the species being
met with skimming over the surface of the sea hundreds of miles
from land. Probably they dive when the surface becomes
ruffled. In these marine genera the abdomen often undergoes
excessive reduction (fig. 5).

Other families of Hemiptera—such as the “Boatmen”
(''Notonectidae'') and the “Water-scorpions” (fig. 6) and their
allies (''Nepidae'') dive and swim through the water. They obtain
their supply of air from the surface. The ''Nepidae'' breathe by
means of a pair of long, grooved tail processes (really outgrowths<noinclude></noinclude>