In most insects that feed by suction the mandibles are modified.
The 'disposition of these valves divides this type of pump into suction pumps and force pumps.
Thus if the instrument depends on the pressure or suction effect alone, and this pressure or suction is measured against the air pressure in an ordinary room, in which the doors and windows are carefully closed and a newspaper is then burnt up the chimney, an effect may be produced equal to a wind of io m.
The other structural characters of the Order may be briefly summarized as: - mouth-parts adapted for piercing and sucking, or for suction alone, and consisting of a proboscis formed of the labium, and enclosing modifications of the other usual parts of the mouth, some of which, however, may be wanting; a thorax fused into a single mass; and legs with five-jointed tarsi.
Larva campodeiform, usually feeding by suction (exceptionally hypermetamorphic with subsequent eruciform instars).