Basically, the body of an ant is divided into head, alitrunk,
petiole and gaster. Some of the major morphological features, which are
important for taxonomic studies, are shown in figure 1.
Fig.1 Diacamma ceylonense,
showing some of the important morphological features used in taxonomy.
The head varies enormously in shape and size (Figs.2-4).
It consists mainly of eyes, clypeus, frons, vertex, genae, antennae and
mouthparts. The size and position of the eyes are highly variable. Sometimes
the absence of eyes also forms an important identifying character for
some species. The mouthparts comprises of mandibles, maxillae, labium
and an unpaired labrum. The region bounded anteriorly by the posterior
end of the clypeus and laterally by a pair of ridges is the frons. Usually,
this is a small and triangular area. The shape, size and the appearance
of the frontal area are highly variable and are very important. The region
between the vertex and the foramen is the occiput. The portion anterior
to the eyes and lateral to the frontal carinae constitutes the gena. Usually,
it is divided into two equal halves by a longitudinal suture. In the frontal
view, mandibles are articulated usually on the lateral corners of the
head and are seen below the clypeus. In some species, the mandibles are
articulated in the middle, as in the genus Anochetus. They are
very variable in shape, size, and dentition are very much important in
ant taxonomy. Other structures like the number of segments on the maxillary
and labial palps are of very important in the diagnosis of the species.
The number of segments, its relative size, and the nature of antennae
also vary greatly with species and are very important. The number of antennal
segments varies from 4 – 12 in workers.
Basically, it is formed of prothorax, mesothorax and metathorax
(fig.5). The lateral sclerites of the thorax are propleuron, mesopleuron
and metapleuron respectively. The metapleuron usually bears a gland, the
metapleural gland. But in all ants, in addition to these three segments,
the tergite of the first abdominal segment is fused to the thorax and
form the propodeum. The thorax varies greatly in shape, size and appearance
with sex, castes and with different species. It bears 3 pairs of jointed
appendages, the legs and the wings (when present).
This portion in ants is highly specialized and consists
of 7 segments. The first segment is fused with the thorax and forms the
propodeum. The second segment is always reduced and is separated from
the remaining abdominal segments and forms a narrow waist and forms the
petiole. Sometimes, the third segment is also reduced and separated to
form the postpetiole. The rest of the segments constitute the proper gaster.
Each abdominal segment consists of a pair of sclerites, a dorsal tergite
and a ventral sternite. In workers, the last abdominal tergite is the
pygidium and the last visible sternite is the hypopygium. In all members
of the subfamily Formicinae, the apex of the hypopygium gives rise to
the acidopore (fig.6). In general, it appears as a short nozzle, usually
with a fringe of short setae at its apex. In most formicines the acidopore
is always exposed, but in some it may be concealed by the posterior margin
of the pygidium. The terminal segment of gaster in females of some species
bears an organ of defense, the sting (fig.7).
As per Bolton (1994), ants bear identification
characters an all parts of the body, and he says, the area around the
clypeus, mandibles and mouthparts is particularly important at the genus
and the species rank.