Internal Anatomy of the Ant


What is inside an ant's body? Do ants have a heart, brain and lungs? How many stomachs do ants have?

Have you ever asked those questions?  Have you ever wondered whether ants have the same organs as we humans do?  On this page I tell you the answers to these questions, and more, as I explain the internal anatomy of the ant.

The Head

The ant’s head contains, among other structures the brain, the oesophagus, pharyngeal gland, the jaw muscles, and part of the heart!

The Brain

An ant’s brain is not quite like a brain that you or I have, but is more a ganglion; a knot of nerves and fibres that sits over the oesophagus, but behind the pharynx 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

Oesophagus is another name for 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). It is 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, however, do eat solid matter.

The Pharyngeal Gland

The pharyngeal gland consists of about 20 finger-like tubes. They contain a yellow oily substance separated from the food, as it travels through the pharynx and into the oesophagus. Some entomologists, believe that the pharyngeal gland provides the ant with a source of energy, and is located just in front of the brain.

Muscles

The inside of an ant’s head is almost all muscle.  The largest muscles control the closing of the jaws, which can exert a lot of pressure. It is certainly enough to pierce the hard cuticle, or exoskeleton of other insects, including other ants. Smaller muscles open the mandibles. Six muscles manipulate the pharynx, to aid in the movement of liquid food from the mouth into the oesophagus.

The Thorax

As we continue our journey inside an ant, we now look at an ant’s thorax. This is the motor-section of the ant’s body. It contains the muscles that operate the legs (and the wings in the queens and males). Also within is the heart, the oesophagus, labial glands and various nerve ganglia.

The Heart

An ant’s heart is nothing like that which 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. It then runs through the thorax and into the abdomen.  

The heart pumps blood throughout the body in one direction. Though to be more accurate, the ant’s heart does not pump in the way our does.  The ant possesses a circulatory system but is not one of veins and arteries. The internal organs are, instead, 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. More on the ant’s “blood” later.

Other parts inside an ant

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 connect 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. This ganglia supplies commands from the brain to the legs and wings for example and carries information from and to the ant’s sensory inputs.

Spiracles.  Strictly speaking, spiracles start on the external side of the ant’s body, but they do extend inwards to the ant’s “circulatory” system. Ants do not have lungs, but obtains its oxygen through the series of spiracles, which are small openings on either side of its thorax.  Oxygen travels the short distant through the spiracles, where it diffuses into the ant’s blood.

Blood, or to be more accurate, haemolymph, is a fluid that bathes the internal organs inside an ant. Haemolymph is equivalent to the blood found in mammals. It contains plasma, cells called haemolytes, as well as various other chemicals.

The Abdomen

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

Two Stomachs

The Crop also called the social stomach, or dry stomach is a small but very expandable stomach that contains no digestive juices. The crop stores liquid for regurgitation to feed other worker ants, the queen, and larvae. It is interesting to note that male ants do not possess a crop stomach.

The main stomach connects to the crop via a valve. The ant can open and close it 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 . It is contaminated with digestive juices from this point on.

Reproduction internal anatomy of the ant - Female

Egg tubes are found in both workers and queens, though those of the latter are far more advanced and numerous. 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 as a single cell, developing as they move along the egg tubes. During the latter stages, the egg develops a skin, called the chorion. Sperm fertilises the egg as it passes down the oviduct. The queen received the sperm during the mating flights and is able to store the sperm alive for 10 years or so in little sacs within her abdomen.

The sperm storage has a valve on it that controls the flow of sperm form the sac to the egg tube, 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. It secretes a fluid that the ant uses as a recruitment trail in order to alert other ants, guiding them to a source of food that another ant has found.

Reproduction internal anatomy of the ant - Male

The reproductive organs of the male ant are physiologically developed to mate with the females, during a single mating flight.  Sperm is produced in the testes, after which the sperm is transferred to the vas deferent, sometimes called the “staging organs.”  Here, the sperm matures and awaits copulation.  

There are also the seminal vesicles, where semen is produced, and the mucus gland.  Prior to copulation the testes, seminal vesicles and mucous glands are engorged, with the associated increase in size.  However, after mating they are depleted of their contents and are subsequently vastly rescued in size to a fraction of what they were before.

Much of the sperm is released in a single mating, though, possibly there is enough left over for a subsequent mating, albeit within the same mating flight.

Once the male has mated and depleted his sperm supply, he very quickly dies. His one and only role in life completed.

External Anatomy of the Ant

If you enjoyed reading about the internal anatomy of the ant, why not pop to the previous page and read up on the external anatomy of the ant.  Click on the button below.

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