External Anatomy of the Ant


You've seen an ant. You know it has a head, a body, six legs and antennae, but what exactly is the body of the ant made up of?

As with all insects, ants have their skeleton on the outside, though it’s not quite like the skeleton we think of such as the one we have inside of us. The skeleton of an ant is called a cuticle, and like our skin, it has many layers making it up. It is hard and offers the ant four things;

A hard-protective covering, like a suit of armour.
A strong base for muscle attachment on the inside.
A filter of dangerous solar rays.
Keeps water vapour inside the ant so that it does not become dangerously dehydrated.

 

Like all insects the ant’s body is made up of three segments:

Head
Thorax
Abdomen
(including a one or two segmented petiole).

 

The Head

An ant’s head has on the outside of it, the jaws (or mandibles), the mouth, the antennae and the eyes.

The jaws, or mandibles, are hollow and are used to pick up their brood, soil, food, rubbish, or even each other.
They can use them to get hold of prey in order to sting, spray with acid, or simply tear apart. They also use them as a means of attack and defensive when fighting, for example, invading ants.
They are also the main utensil used for creating new chambers and tunnels in their nests. Their jaws can close with such force that some species of ant, such as the soldier of the Leafcutter, can cut through leather. Some tribes in Africa also use the jaws of an ant as stitches to close wounds on people; the grip is that strong. The jaws usually have little teeth on them, being larger at the front of the jaw and smaller at at the back, which help the ant grip things. They are strong enough to puncture the bodies of their prey/enemies yet gentle enough to tenderly pick up their brood (‘babies’), much like the teeth of a cat that can tear meat from bones, yet gentle enough to carry kittens about in their mouths.

The ant’s mouth contains a tongue which is used to taste and ‘lick’ their food. It doesn’t have muscles to move it as we humans do, but rather it uses blood pressure to cause the tongue to project out of its mouth. When an ant, for example, drinks water it doesn’t lap it like a cat but places its tongue on the water which then travels up the tongue, into the mouth, and down its digestive tract.
Like a cat’s tongue it has striations on it (that’s what makes a cat’s tongue feel rough when it licks you), and it also uses its tongue to wash itself, similar to how a cat does, (there are a lot of similarities it seems between cats and ants!).  A cat will lick its paw and then wipe that paw over its head, whereas an ant does the same, only in reverse. The ant will rub its legs over its body and then transfer the dirt to its front legs, and then it will pass its front leg over its mouth where the dirt is captured into a little pocket, called the infra-buccal pocket, just below the mouth. Once this pocket is full it will empty it into a rubbish pile usually outside of the nest.

The antennae are perhaps the most important sensory organ that the ant possesses and acts as the ant’s sense of sight, hearing and taste. It might seem odd to say that the antennae act as eyes when in fact the ant already has eyes, but the eyes of ants are generally not that good at seeing. They can detect light, particularly ultraviolet light, but as you can probably imagine when underground the ant’s eyes see nothing at all. Instead the ants rely on their antennae to act as their primary sense of seeing and hearing. They can detect chemicals in the air, scent trails on the ground, and are sensitive to air pressure changes and vibrations. They are hinged roughly about halfway down their length, which is one of the identifying features of ants, and are very mobile, being able to sweep through the air or come together to feel something on the ground that is less than one millimetre in size.

When an ant gets into a dangerous situation, such as attacking prey or enemy ants, the antennae can be folded back across the head to protect them.

The Eyes are compound in structure, meaning that they are made up of many individual lenses, like that of a fly. Different species of ant have different numbers of lenses (or ommatidia to give them their proper name). For example, the yellow meadow ant Lasius flavus have 45 ommatidia per eye, whereas in Formica cunicularia there are 460. In Lasius niger, 120, and in some army ants, only one. As mentioned above ants generally have poor eyesight but some can make out landmarks and detect movement. I used to keep a colony of Formica fusca and these seemed to have good eyesight for ants as they would see me approaching their tank from across the room.

Flying ants have three light sensitive cells on the top of their heads which, it is believed, assist in navigation when flying.

The Thorax

The ant’s thorax, sometimes called the mesosoma, is the middle section of the ant’s body from which the six legs emerge. In worker ants it is a rigid, complete fixture though does have fused segments within it. The thorax segments in the queen ant are flexible which helps the use of the wing muscles. Along the thorax, too small to be seen by the naked eye, are spiracles, which are tiny inward facing tubes through which air enters the ant’s body, much like our trachea, though the ant does not have lungs with which to inhale and exhale the air. The thorax also has two ducts from which a greasy substance is produced which is used to keep the ant clean from infection and may also be part of the source of the ant’s colony scent, which helps ants distinguish nest mates from enemy ants. The thorax sometimes has, depending on species, backward facing spines on the rear edge, which is used to help protect the ant’s body.

Each of the legs has five main joints with the distal end (the outer most) being further sub-divided to make up the foot which ends in two curved claws. The legs of an ant are adapted superbly for movement over uneven ground and they can even climb smooth surfaces such as glass. The front legs have fine hairs on them that act as a comb as a means of cleaning itself.

The Abdomen

Finally, there is the abdomen which is made up of a series of plates connected by an elastic tissue. The plates tuck in under one another along their leading edge, but when the ant’s stomach is full these plates can stretch apart and the underling elastic connective layer can be visible as pale bands. The abdomen also contains the sting, species dependant, which is smooth, not barbed like the honeybee’s. At the tip is also the scent glands which are used, primarily, to lay scent trails down to help other ants locate a discovered food source. Some ants also emit formic acid from the tip of the abdomen which is another method of defence. The first one or two segments of the ant’s abdomen are constricted into a waist like appearance called a petiole which connects the abdomen to the thorax. Some ants have a single segmented petiole, whereas others have two. The segments enable the ant to bring the abdomen underneath its own body for cleaning and sting/formic acid use.

I do intend to put a labelled diagram of the external details of the ant, but I don’t want to just copy one from the Internet without permission. Please bear with me on this.