Ants breathe through a network of air-filled tubes called tracheae that deliver oxygen directly to their tissues, bypassing any need for lungs or a blood-based oxygen transport system. Air enters through tiny valve-like openings called spiracles, arranged along the sides of the body, and flows inward through progressively smaller branches until it reaches individual cells. The system is surprisingly sophisticated, with different spiracles playing different roles and the breathing pattern itself shifting between rest and activity in ways researchers are still working to fully understand.
Spiracles Are Not All Created Equal
An ant’s body has spiracles on both its thorax (the middle segment) and its abdomen (the rear segment), but these two groups of openings are far from interchangeable. In the Saharan silver ant Cataglyphis bicolor, thoracic spiracles handle roughly 80 to 90 percent of all gas exchange when the ant is active. A single open thoracic spiracle can supply enough oxygen and vent enough carbon dioxide to meet the ant’s resting needs all on its own. The abdominal spiracles, by contrast, have less than half the gas-moving capacity of a single thoracic spiracle, even when all of them are working together.1Journal of Insect Physiology. Ventilation in Cataglyphis bicolor: Regulation of carbon dioxide release from the thoracic and abdominal spiracles
That does not mean the abdominal spiracles are useless. They play an important role during specific phases of the ant’s resting breathing cycle, particularly in the early stages of a “flutter” phase when they open and close in a rapid, flickering pattern before the thoracic spiracles take over. The two sets of spiracles actually show inverse coordination during this phase: as the abdominal spiracles ramp down, the thoracic ones ramp up.1Journal of Insect Physiology. Ventilation in Cataglyphis bicolor: Regulation of carbon dioxide release from the thoracic and abdominal spiracles
Each spiracle acts as a muscular valve, and the ant controls whether it is open, partially open, or sealed shut. When metabolic demand is high, the spiracles stay wide open and air flows freely. When demand drops, spiracles close partially or completely, shifting the breathing pattern into something more intermittent.2Dove Medical Press. Recent insights into sublethal effects of pesticides on insect respiratory physiology
Inside the Tracheal Network
Behind each spiracle sits a branching tree of tubes. The largest tracheae are wide enough to see under a basic microscope, but they subdivide into ever-finer branches called tracheoles that penetrate deep into muscles, nerve tissue, and organs. The oxygen does not need to be carried by blood. It diffuses directly from the air inside these tiny tubes into the cells that need it, which is one reason insects can function with an open circulatory system that does not need hemoglobin the way vertebrate blood does.
For decades, biologists assumed that as tracheal tubes branched, the combined cross-sectional area of the child branches would equal or exceed the area of the parent tube, similar to how arteries branch in mammals. A study of 20 ant species found the opposite. In ants, the total cross-sectional area actually shrinks at each branching level. Instead of area being preserved from parent to child branches, it is the radius that is conserved: the summed radii of the daughter branches roughly equal the radius of the parent tube.3PLOS Computational Biology. Tracheal branching in ants is area-decreasing, violating a central assumption of network transport models This matters because many theoretical models of how insect respiratory networks deliver oxygen had been built on the assumption that area increases at each branch point. The ant data suggest those models need rethinking, at least for this group of insects.
Researchers have also gotten a direct look at how these tubes move in living insects using synchrotron X-ray imaging, a technique that produces high-resolution video of internal structures in real time. In beetles, crickets, and ants, the scans revealed rapid cycles of tracheal compression and expansion in the head and thorax, showing that the tubes are not rigid pipes but flexible structures that can actively pump air.4PubMed. Tracheal respiration in insects visualized with synchrotron x-ray imaging
The Breathing Pattern at Rest
When an ant is sitting still, it does not breathe continuously. Instead, many species use a pattern called the discontinuous gas exchange cycle, or DGC, which has three distinct phases. During the closed phase, the spiracles are shut and very little gas moves in or out. During the flutter phase, the spiracles open and close rapidly in tiny bursts, letting a small amount of oxygen in while keeping carbon dioxide mostly trapped. Then comes the open phase, when the spiracles open wide and a burst of accumulated carbon dioxide is released all at once.
This cycling has been documented across multiple ant species. In fire ants, all castes (workers and both male and female winged reproductives) exhibit DGCs at cooler temperatures. The pattern becomes harder to maintain as conditions warm up. At 30°C, only workers and male alates still showed clear discontinuous cycling; females had shifted to something more continuous.5Journal of Insect Physiology. Discontinuous gas exchange in the fire ant, Solenopsos invicta Buren: Caste differences and temperature effects The frequency of the cycles also speeds up with temperature, which makes intuitive sense: warmer bodies burn energy faster and need to exchange gases more often.
In leaf-cutter ants, the DGC pattern scales with body size in a predictable way. Larger workers cycle more slowly but release far more carbon dioxide per burst. The biggest workers in a colony release about 40 times more carbon dioxide per burst than the smallest ones.6Biology Letters. The allometry of discontinuous gas exchange cycles in Atta cephalotes leaf-cutter ants This is not just a quirk of measurement. An ant’s resting metabolic rate is determined largely by how often these bursts happen and how much gas each one releases, so body size directly shapes how the respiratory system operates.
Active Ventilation and Abdominal Pumping
For a long time, many entomologists assumed that gas exchange in small insects was mainly passive, driven by diffusion alone. That picture has gotten more complicated. In forager ants of Formica polyctena, researchers observed that each burst of carbon dioxide release during the open phase was accompanied by telescoping movements of the abdominal segments: rapid contractions followed by slow relaxations, essentially a pumping action that pushes air through the tracheal system.7Physiological Entomology. Cyclic release of carbon dioxide accompanied by abdominal telescoping movements in forager ants of Formica polyctena (Hymenoptera, Formicidae) So while diffusion is important, at least some ants actively ventilate their tracheal system by physically squeezing their abdomen.
This makes more sense when you consider how the tracheal system is built. The area-decreasing branching pattern described earlier means gas faces more resistance as it moves deeper into the network. Active pumping could help overcome that resistance, especially during the open phase of the DGC when a large volume of carbon dioxide needs to exit quickly.
What Changes When Ants Start Moving
The careful, intermittent breathing pattern of a resting ant disappears the moment it starts walking. Walking ants breathe continuously, with spiracles open and gas flowing in and out without the rhythmic start-stop of the DGC. The metabolic cost is substantial. In Camponotus carpenter ants, walking on a level surface at a slow pace increased metabolic rate about four times over resting levels. At higher speeds or on a 30-degree incline, the metabolic rate jumped to nearly seven times the resting rate.8Journal of Experimental Biology. Walking on inclines: energetics of locomotion in the ant Camponotus
One interesting finding from the same study: walking uphill or downhill on slopes up to 60 degrees had only a small effect on energy consumption compared to walking on a flat surface. The main driver of metabolic cost was speed, not slope. This is unusual compared to larger animals, where climbing a hill is much more expensive than walking on the flat. It likely reflects the ant’s tiny mass and the relatively low cost of lifting such a small body against gravity.
Does Closing Spiracles Save Water?
A common explanation for why insects evolved the DGC is water conservation. The logic seems straightforward: keeping the spiracles sealed most of the time should reduce the amount of water vapor that escapes from the moist internal surfaces of the tracheal tubes. This is a tidy story, and it appears in many textbooks, but the evidence from ants specifically is not very supportive.
In harvester ants of the genus Pogonomyrmex, researchers measured both respiratory water loss and total water loss. Respiratory water accounted for less than 5 percent of the total water an ant lost. The researchers concluded that discontinuous ventilation probably does not function primarily as a water-saving strategy in these ants, though it might serve other purposes.9Physiological Entomology. Respiratory physiology and water relations of three species of Pogonomyrmex harvester ants (Hymenoptera: Formicidae) The water-conservation hypothesis has not been abandoned entirely across all insects, but for ants, the respiratory system may simply not be a major route of water loss. Most of their water escapes through the cuticle, the waxy outer shell, rather than through the spiracles.
Alternative explanations for the DGC include protecting tissues from oxidative damage by keeping internal oxygen levels low during the closed phase, or preventing excessive oxygen from reaching sensitive tissues. There is no consensus yet, and it is possible the DGC serves different functions in different species or environments.
Temperature, Size, and Caste
An ant’s breathing pattern is not fixed. It responds to temperature, body size, and even the ant’s role in the colony. In fire ants, the DGC frequency at 15°C was as low as 0.9 millihertz in male alates (winged reproductives), meaning the spiracles opened for a burst of gas exchange less than once every 18 minutes. At 30°C, workers cycled at up to 18 millihertz, roughly once per minute. The temperature sensitivity was striking, with Q10 values above 4 for all castes, meaning the cycle frequency more than quadrupled for every 10°C rise in temperature.5Journal of Insect Physiology. Discontinuous gas exchange in the fire ant, Solenopsos invicta Buren: Caste differences and temperature effects
Caste differences add another layer. Workers, which are the smallest fire ant caste, cycle fastest. The larger winged reproductives cycle more slowly but exchange more gas per cycle. The volume of each carbon dioxide burst also changes with temperature: cooler temperatures produce bigger, less frequent bursts, while warmer temperatures produce smaller, more frequent ones. The whole system adjusts dynamically based on what the ant’s body demands at any given moment.
How Larvae and Pupae Breathe
Ant larvae and pupae have tracheal systems too, but their respiratory rates vary enormously depending on the developmental stage. In Camponotus rufipes, first-instar larvae had the highest weight-specific oxygen consumption of any life stage, roughly ten times higher than that of pupae. That early spike likely reflects the intense metabolic cost of tissue differentiation happening in the first larval stage. As larvae grow through subsequent instars, their mass-specific respiratory rate drops sharply, continuing to decline through the prepupal and pupal stages.10ScienceDirect (Elsevier / Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology). Respiratory Metabolism of Camponotus rufipes Ants: Brood and Adults
Adult workers actually showed a higher mass-specific metabolic rate than late-instar larvae or pupae, which makes sense given how physically active adult workers are compared to the sedentary brood. The pattern highlights that the respiratory system is not just a fixed piece of hardware but a system whose demands and performance shift across an ant’s entire life.
Surviving Underwater in Mangrove Nests
Perhaps the most dramatic respiratory adaptation in ants belongs to Camponotus anderseni, a species that nests inside mangrove branches in northern Australia. Twice a day, tidal flooding completely submerges their nests for up to three hours at a time. When the tide rises, a soldier ant plugs the nest entrance with its head, sealing out the water but also cutting off fresh air.
Inside the sealed nest, oxygen drops steeply and carbon dioxide climbs. After just one hour in sealed laboratory nests, oxygen concentration fell by nearly 7 percent while carbon dioxide rose by about 12 percent. The disproportionate increase in carbon dioxide compared to the drop in oxygen suggests the ants partially switch to anaerobic metabolism, producing energy without oxygen at the cost of efficiency. The ants also drastically suppress their respiratory rates during submersion, an extreme physiological depression that lets the colony survive on the limited air trapped inside.11Physiological Entomology. Respiration by mangrove ants Camponotus anderseni during nest submersion associated with tidal inundation in Northern Australia
This is not hibernation or a slow shutdown. The ants resume normal activity almost immediately after the tide recedes and the nest entrance is reopened. The ability to toggle between normal aerobic respiration and a deeply suppressed, partly anaerobic state twice daily is unusual even among insects and points to how flexible the tracheal respiratory system can be when selection pressure demands it.
How Pesticides Disrupt the System
Because the tracheal system depends on precise control of spiracle opening and closing, anything that interferes with that muscular control can wreck an ant’s ability to breathe properly. Many insecticides target the nervous system, and since the spiracle valves are governed by neural signals, poisoned ants often lose the ability to regulate gas exchange. Spiracles may lock open, causing excessive water loss, or lock shut, depriving tissues of oxygen. Sublethal pesticide exposure can disrupt the DGC pattern without immediately killing the ant, leaving it energetically compromised and more vulnerable to environmental stress.2Dove Medical Press. Recent insights into sublethal effects of pesticides on insect respiratory physiology
This vulnerability extends beyond pest-control contexts. Non-target ant species exposed to drifting agricultural pesticides can experience the same respiratory disruption, which may explain some of the broader ecological effects that field-applied insecticides have on ant communities. The respiratory system, precisely because it relies on such fine-tuned valve control, turns out to be one of the more fragile systems in the ant’s body when chemistry gets involved.
What Decapitation Experiments Revealed
One of the more unsettling tools in ant respiratory research is decapitation. Ants can survive for hours or even days without a head, and this allows researchers to study what the thoracic and abdominal ganglia (local nerve clusters) can do on their own without input from the brain. In harvester ants, decapitated individuals continued to exhibit discontinuous ventilation, confirming that the DGC is not coordinated by the brain. Instead, local nerve centers in the thorax and abdomen maintain the breathing rhythm independently.9Physiological Entomology. Respiratory physiology and water relations of three species of Pogonomyrmex harvester ants (Hymenoptera: Formicidae)
Decapitation did lower overall metabolic rate and reduced the frequency of gas exchange bursts, which makes sense given that the head contains metabolically active tissue including the brain. But the basic pattern persisted. This tells us something fundamental about insect respiratory control: the breathing rhythm is distributed across the body rather than centralized in a single control center, a design that is radically different from how vertebrates manage respiration.