Ants, like all other insects, do not possess the red fluid recognized as blood in vertebrates. Instead, their circulatory fluid is called hemolymph. This fluid serves multiple functions but fundamentally differs from mammalian blood by not being the primary carrier of oxygen.
Hemolymph vs. Vertebrate Blood
Vertebrate blood contains red blood cells and hemoglobin to transport oxygen, giving it a red color. Hemolymph lacks these specialized oxygen-carrying cells and appears clear, pale yellow, or sometimes greenish. The fluid is mostly water, containing a complex mixture of inorganic salts, amino acids, sugars, lipids, and proteins.
Hemolymph contains specialized cells called hemocytes, which function similarly to mammalian white blood cells. These cells are suspended in the plasma and play a strong role in immune defense and wound healing. They actively attack foreign invaders, such as parasites and bacteria, and are involved in the clotting process following injury.
How Ants Breathe Without Oxygen-Carrying Fluid
Ants do not require an oxygen-carrying fluid because of their specialized respiratory system, known as the tracheal system. This system is a network of air-filled tubes that permeates the entire body, delivering oxygen directly to every tissue and cell. It bypasses the need for the circulatory fluid to be involved in gas transport.
Air enters the ant’s body through tiny, paired external openings called spiracles, located along the sides of the thorax and abdomen. Ants possess nine to ten pairs of these openings, which they can open and close to regulate air intake and prevent water loss. From the spiracles, air moves into progressively smaller tubes called tracheae, which branch extensively throughout the internal structures.
The tracheae narrow into microscopic tubes called tracheoles, which end directly at or near the surface of individual cells, allowing for the direct diffusion of oxygen. Passive diffusion is often sufficient for small insects. However, more active species may use rhythmic contractions of abdominal muscles to pump air through the tracheal network, increasing gas exchange efficiency.
The Non-Respiratory Roles of Hemolymph
While not involved in respiration, hemolymph performs several other functions, acting as a transport and regulatory medium. Its main purpose is to carry nutrients, such as sugars, lipids, and amino acids, from the digestive system to the organs and tissues. It also transports hormones that regulate growth and development throughout the body.
Hemolymph collects metabolic waste products from cells and carries them to the excretory organs, specifically the Malpighian tubules, for elimination. Another important function relates to mechanics and movement. The fluid maintains hydrostatic pressure within the body cavity, known as the hemocoel. This internal pressure assists in physical processes, such as the expansion of the body after molting or the extension of legs and antennae.
The Open Circulatory System
Ants, like most arthropods, have an open circulatory system, meaning the hemolymph is not confined to arteries and veins. Instead, the fluid flows freely throughout the hemocoel, directly bathing all internal organs. The primary structure for moving this fluid is the dorsal vessel, a long, tubular organ running along the upper side of the ant’s body.
The dorsal vessel is divided into two sections: the heart, located in the abdomen, and the aorta, extending forward into the head. The heart is a muscular, contractile tube that uses rhythmic contractions to pump the hemolymph forward. Hemolymph enters the heart through small, valved openings called ostia and is propelled into the aorta, which discharges the fluid into the head capsule. The hemolymph then flows backward through the hemocoel, circulating around the internal organs before re-entering the heart through the ostia.