What is an Ant?
While ants are
one of the most familiar insects and can be reliably identified by
even the youngest naturalist, what exactly is it that makes an ant
an ant? There are several traits which will separate them from other
insects. First, all ants have either a single small, distinct segment,
, or two small segments,
the petiole and postpetiole
(click these terms to see their definitions). These separate segments
are absent from almost all other insects other than a few groups of
wasps. A character which is found only in ants is the metapleural
. This gland is found on the side of the propodeum
just above the hind leg and has a small opening to the outside of
the body. It should be noted that while this gland is found only in
ants, not all ants have a metapleural gland. A few genera in the subfamily
(such as Camponotus
have lost the metapleural gland and its associated opening.
In addition to these two
characters, there are several other distinctive traits of ants. One
is their elbowed antennae
. The first
segment of the antenna, the scape
much longer than the remaining segments, the funiculus
and the joint between them is highly flexible. During normal activity
the scape is held upright and near the head with the funiculus projecting
forward in front of the body. This arrangement allows the tips of
the antennae to be positioned near the mouthparts to assist in inspecting
nearby objects, or to be extended forward away from the body to investigate
more distant items. While a sting
present in many ants, it is absent in several large and common groups
and is of little use in separating ants from many other insects.
Keys are used
to identify and name specimens. On this site there are three sets
of keys: a single key to identify subfamilies, a series of keys to
identify genera within each subfamily and keys to indentify species
within genera (these last keys are only available for selected groups).
These keys are called dichotomous
keys. This is because they are composed of paired, contrasting descriptions.
Together, the two descriptions (or lugs) comprise a couplet. A specimen
is compared with each of the descriptions (lugs) in a couplet and
the most appropriate description is selected. In printed versions
of keys each
description ends in either a number or a name. The
number indicates the couplet to proceed to next to continue the identification,
while a name indicates that the identification is complete and the
specimen in hand belongs to (or is likely to belong to) that group.
A typical printed couplet looks similar to this:
Eyes small, with at most 4 facets (ommatidia) in greatest diameter,
and round or nearly round (Fig. a) .......................Anisopheidole
Eyes large, with 8 or more facets (ommatidia) in greatest diameter,
and distinctly oval or elongate (Fig. aa) ....................................41
This site also contains
online versions of these keys (for example, Key
to Subfamilies). These keys work in essentially the same way but
are clickable with links to the next couplet and to taxon details.
A typical page (or couplet) for these keys is similar to this:
Key to the Subfamilies
Previous Step | Start Over
and linear, with teeth only at the extreme tip (fig. a), and
attached close together along the front margin of the head (fig.
with teeth along the entire inner margin (fig. aa), and with
their attachments at the outer corners of the front margin of
the head (fig. bb).
3 taxa: Dolichoderinae, Formicinae,
This is an example only and there are no actual links in the table above.
The upper panel or cell
contains a description of the characters being used while the middle
panel illustrates these characters. The bottom panel contains a list
of the taxa which share these characters. Clicking on the arrows in
the upper panels or the figures in the middle panels will move to
the next couplet while selecting a name in the lower panel will jump
to the details for that taxon. When only a single name remains in
the lower panel the identification is complete.
When Things Go Wrong
In some cases
none of the characters listed in either lug of a couplet will seem
appropriate or the characters in a lug only partially match the specimen.
In these cases it is likely that a mistake was made earlier in the
key and that the specimen was not intended to run to this part of
the key. When this happens the previously used couplets should be
rechecked to determine if an incorrect lug was selected. A trick used
by experienced key users is to note any "problem" or ambiguous
couplets during an identification. Later, if the key becomes difficult
to use because the characters seem inappropriate, the other lug of
the "problem" couplet is tried. If a mistake was indeed
made, the other path through the key will often run much more smoothly
and the characters used will better fit the specimen in hand.
Confirming an Identification
Keys are only
the first step in the identification process. Once a name is found,
it is wise to check additional information to confirm that the name
seems reasonable and appropriate for the specimen. This additional
information can include overall similarity of the specimen to other
members in the suspected group, the description listing detailed unique
or diagnostic characters, the habitats used by the group and the known
distribution of the group. If any of these seem inappropriate, the
identification should be treated cautiously until it can be confirmed
by comparison with reliably determined material or by a taxonomist
experienced with the group.
Using the Keys
The keys are designed
to identify workers only. This is because workers are by far the most
commonly encountered caste of ants and the best known taxonomically.
Because queens, and especially males, are much less common it is often
very difficult to identify them, even in cases where the workers are
common and well known.
The characters used in
the keys are limited to those found on the outside of the body. In
addition every effort has been made to select easily observable and
unambiguous characters. However, the small size of ants means that
reliable identification is only possible with the use of a microscope.
The maximum magnification necessary will vary with the specimen being
examined, but a range of 10X to 50X will generally be required. In
a few cases higher magnification is desirable although not essential.
Then using any microscope illumination is important. For example a
low quality light source will degrade the image seen through even
an expensive microscope. Additionally, some types of illumination
will cause bright reflections to appear on the surface of the specimen
which will obscure the pattern of the surface sculpturing. Because
of this it is important to consider a range of light sources when
choosing a microscope and illuminator.