Internal Anatomy of the Ant

Let's talk about what is inside an ant's body

The Head

Inside the ant’s head can be found, among other structures the brain, the oesophagus, pharyngeal gland, the jaw muscles, and part of the heart!

The brain is not quite like a brain that you and I have, but it is more a ganglion, a knot of nerves and fibres that sits over the oesophagus but behind the pharynx, which is part of the gut.  The brain is able to store simple information but allows the ant to process quite complicated sensory data that it receives from its antennae, joints, body hairs and eyes. This gives the ant the ability to work out its environment and to react accordingly.  It can also store memory information, allowing it to remember landmarks and its way back home.

The oesophagus is the ‘food pipe’ that takes liquid food from the pharynx, part of the mouth, into the crop (also known as the social, or dry stomach), located within the ant’s abdomen. It is interesting to note that most ants do not eat solid food, but rather live on a liquid diet from the prey that they find and kill.  Ant larvae does eat solid matter.

The pharyngeal gland is made up of about 20 finger-like tubes which contain a yellow oily substance separated from the food, as it travels through the pharynx and into the oesophagus. It is thought to provide ant with a source of energy, and is located just in front of the brain.

Muscles almost fill the head of the ant, with the largest muscles controlling the closing of the jaws, which can exert a lot of pressure, at least for something the size of an ant. It is certainly enough to pierce the hard cuticle, or exoskeleton of other insects, including other ants. Smaller muscles are used to open the mandibles whilst six other muscles are used to manipulate the pharynx to aid in the movement of liquid food from the mouth into the oesophagus.

The Thorax

The thorax of the ant is the motor-section. Not only does it have the muscles that operate the legs (and the wings in the queens and males) but also within it is the heart, the oesophagus, labial glands and various nerve ganglia.

The heart of the ant is nothing like that we or other mammals have, it is in fact more like one of our veins. The heart of the ant actually starts in the head, just behind the brain, and runs through the thorax and into the abdomen.  Blood is “pumped” (though to new more accurate, the ant’s heart does not pump in the way our does), throughout the body in one direction, though not in a circulatory system of veins and arteries as we have, but instead all the internal organs are bathed in a fluid which the long tube-like heart supplies.  The heart has valves in it, again much like a human vein, which prevents the blood flowing back on itself. Though I say the word  ‘blood’, the ant does not have blood as we know it, but instead it has a clear/yellowy fluid. This fluid does not carry gases but filters through the internal organs. Gases, such as air, are transported to the various tissues and organs directly by the spiracles.

The oesophagus, which we have briefly spoken about above, travels through the thorax on its way to the pair of stomachs in the abdomen.

The labial glands are connected to the tip of the tongue in the head via a long thin duct. The labial glands secrete a watery lubricant like substance which aids in the digestion of food.

Nerve ganglia run throughout the thorax from the brain to the abdomen, underneath the heart and labial glands. They are used to supply brain commands to the legs and wings for example,  and carries information from and to the ant’s sensory inputs.

The Abdomen

The abdomen is the final section of the ant and contains, among many other things the crop, the stomach, the heart, egg tubes and duct, sting/formic acid duct and the Dufour’s Gland.

The Crop, also called the social stomach or dry stomach is a small but very expandable stomach that contains no digestive juices. It is used to store liquid for regurgitation to feed other worker ants, the queen and larvae.

The stomach is connected to the crop via a valve that the ant can open and close in order to move food from the crop to its own stomach, to provide sustenance to its own body. Once food passes from the crop to the main stomach it cannot be passed back into the crop as it would be contaminated with digestive juices.

Egg tubes are found in workers and queens though those of the latter are far more advanced and numerous than the former. These tubes start at the front of the abdomen, below the heart, ending up at the tip of the abdomen. In the queen the eggs start at one end as a single cell, developing as they move along the egg tubes. During the latter stages the egg develops a skin, called the chorion, and then is fertilised by sperm that the queen has stored in special little sacs within her abdomen. She received the sperm during the mating flights and is able to store the sperm alive for 10 years or so. The sperm storage has a valve on it that controls the flow of sperm form the sac to the egg tube, so fertilising any egg that passes through. The amazing thing is that the queen can allow a developing egg to pass through without being fertilised. In these instances, the unfertilised eggs develop into winged males.

The sting or formic acid duct, dependant on species, is found at the tip of the abdomen. There is a poison sac that delivers poison to the sting, formic acid or other sticky fluids used in defence.

The Dufour’s gland is a small gland near then tip of the abdomen that secretes a fluid that the ant uses as a recruitment trail in order to alert other ants, and guide them to a source of food that another ant has found.

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.