Glossary of Terms Used in the Keys and Descriptions
The ant’s body
is divided into four main sections. The head
is the first section, followed by the large mesosoma
the small petiole
and sometimes the
, and finally the gaster
The head carries the antennae
the three pairs of legs
are attached to
the lower surface of the mesosoma and the gaster terminates with a defensive
structure (often a sting
Although the mesosoma and gaster appear to correspond to the thorax
and abdomen of most other insects, this is not the case. The rear section
of the mesosoma, the propodeum, is actually the first abdominal segment,
the petiole is the second segment and the postpetiole, when present,
the third segment. The gaster is composed of the remaining segments
of the abdomen.
The most important taxonomic structures on the head are the antennae,
palps and clypeus. The antennae are composed of two major parts,
the long first segment, the scape, which is attached to the head,
and the remaining shorter segments, collectively called the funiculus.
The important characteristics of the antennae include the number of
segments (when counting the number of segments, the scape is always
included), the length of the scape (usually in relation to the length
of the head), and, in some groups, the position of antennae when at
rest against the front of the head.
are small, segmented, sensory organs found on the mouthparts and are
visible on the underside of the head behind the mandibles. There are
two pairs, the outer pair situated on the maxillae (called the maxillary
palps) and the inner pair situated on the labium (called the labial
palps). The number of maxillary palp segments varies from 6 to 1 (with
6 being the most common) and the number of labial palp segments varies
from 4 to none with (4 being the most common). The palp formula
is the standard method used to indicate the number of palp segments
and is composed of the number of maxillary palp segments followed by
the number of labial palp segments. For example, a palp formula of 6:4
would indicate that the maxillary palps have 6 segments while the labial
palps have 4 segments.
is the plate on the lower section of the front of the head above the
mandibles and below the antennae. Its lower edge (above the mandibles,
here called the front margin) is usually convex in overall shape, but
can be highly modified with concave regions, teeth or variously shaped
projections. The rear section (near the antennae) is usually narrowed,
convex or triangular and often extends between the forward sections
of the frontal lobes. The central region of the clypeus is usually smooth
and gently convex across its entire width, although in some groups it
may have a pair of weak to well-developed, diverging ridges (in which
case the clypeus is described as being longitudinally bicarinate).
In some groups
the shape of the frontal carinae
is important. The frontal carinae
are a pair of ridges on the front of the head; these ridges start just
above the clypeus and between the antennal sockets and extend upwards.
Their development varies from being very short, weakly developed or
even absent to very distinct and running the length of the head. The
lower section of the frontal carinae is often expanded towards the sides
of the head and partially or completely covers the antennal sockets.
In these cases this section of the frontal carinae is called the frontal
features on the head include the compound eyes
(which vary in
size, shape and position, and can be absent), the position of the antennal
(the points where the antennae attach to the head), the
development of a psammophore
(a collection of long hairs on the
underside of the head), the presence of antennal scrobes
depressions or grooves on the front of the head which receive the scapes
when at rest), and the shape of the mandibles
including the number
and placement of teeth.
, also called the alitrunk, is the middle section
of the body to which the legs are attached. It is behind the head and
in front of the petiole. In workers the mesosoma is relatively simple,
with a limited number of sutures and plates. Queens, however, have a
much larger mesosoma with many sutures and plates. This additional complexity
is required because queens typically have wings during the early part
of their lives. The larger mesosoma houses the flight muscles and the
additional sutures and plates are used to control the wings during flight.
has numerous structures of taxonomic importance. The upper surface (tergite)
of the first segment, immediately above the front legs, is called the
. In most ants the pronotum forms a separate, distinct
plate but in some it is fused with the sclerite behind it, the mesonotum,
to form a single plate. The mesonotum
is the upper surface of
the mesosoma behind the pronotum and in front of the metanotal groove.
It is essentially the central one-third of the mesosoma and has the
middle pair of legs attached to its underside. The metanotal groove
is an angle or depression on the upper surface of the mesosoma which
separates the mesonotum and the propodeum. In some groups the metanotal
groove is lacking and the upper surface of the mesosoma is uniformly
arched when viewed from the side. The propodeum
is the rear section
of the mesosoma, above the hind legs and immediately before the petiole.
The metapleural gland
, or more correctly, its opening, is located
on the side of the propodeum immediately above the hind leg and below
the propodeal spiracle, near the attachment point of the petiole. Its
small opening is often surrounded by tiny ridges or is located in a
shallow, elongate depression. The opening is often protected by a fringe
of elongate hairs or setae. In a few groups the metapleural gland is
absent and the area above the hind leg is smooth.
The legs are composed of five main segments. The segment nearest
the body is the coxa, followed by the very short trochanter
(which is seldom used in ant taxonomy), the long femur and tibia,
and finally the tarsus. The tarsus is composed of five small
segments with a pair of small, curved claws at its tip. The claws
are most commonly a single, curved shaft terminating in a sharp point.
However, in some groups the claws can have from one to many small teeth
along their inner margins. The junction of the tibia and the tarsus
is usually armed with a large, stout, articulated, spike-like structure
called the tibial spur. The number of spurs can be none, one
or two, and they can be simple or comb-like (pectinate). These
structures are best viewed from the front with the leg extending outwards
from the body at right angles to its long axis.
Petiole and Postpetiole
is the first segment behind the mesosoma and is present
in all ants. Behind the petiole is either the postpetiole
. The postpetiole is found in only some subfamilies
of ants. When present, it forms a distinct segment separate from the
gaster. The upper surfaces of the petiole and postpetiole are often
high and rounded or angular. This upright structure is called the node
In some cases the node is absent and the petiole is low and tube-like.
The narrow forward section of the petiole in front of the node is called
. This section can be long, short or absent. In many
groups there is a subpetiolar process, a projection or lobe on the underside
of the petiole near its attachment to the propodeum. This process varies
from being absent to thin and pointed to broad and rounded.
and postpetiole provide a flexible junction between the mesosoma and
gaster. This allows an ant to bring the tip of the gaster forward towards
the front of its body. In this position the sting or the opening for
the defensive system can be used to subdue prey or attack intruders.
The last segment of the body is the gaster. In most ants
it is smooth in outline, but in some the first segment is separated
from the remainder by a shallow constriction, and in a very few each
segment is separated by shallow constrictions. A sting is often
visible at the tip of the gaster, although it is retractable and may
not be visible even when present. In some ants the sting is absent and
the tip of the gaster terminates in a small, slit-like or circular,
glandular opening. Finally, the upper plate (tergite) of the last segment
of the gaster is called the pygidium.
There are a number of terms used for general structures found on
ants. A seta is an elongate hair ranging from upright and standing
above the body’s surface to appressed against the surface. A spiracle
is a small opening in the body which is part of the respiratory system.
The most obvious spiracles are generally those near or in the metanotal
groove and on the sides of the propodeum. The shape and location of
the propodeal spiracle can be of significant taxonomic importance. A
suture is a line or impression formed where two body plates or