How Do Dragonfly Nymphs Breathe Underwater? The Rectal Gill Explained

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How do dragonfly nymphs breathe underwater? They use a structure at the end of the gut. A study of their oxygen intake describes the strategy as “tidal ventilation,” and the nymphs draw water in and push it out through the same opening. The gill is a modified part of the rectum, which is an unusual arrangement among water breathers. This article explains how the rectal gill works, how the nymph moves water through it, and what the study shows about low-oxygen water.

Quick answer

• Dragonfly nymphs “breathe water using tidal ventilation,” which the study calls “a highly unusual strategy in water-breathing animals.”
• The gill sits at the rear of the body. The study says the nymphs “modified the terminal segment of their rectum into a branchial basket.”
• To cope with low oxygen, the nymphs breathe faster. The study reports that “ventilation frequency increased significantly” when oxygen fell.
• The study finds the nymphs “maintain their OEE during hypoxia,” where OEE is oxygen extraction efficiency.

Why water is hard to breathe

Water is a difficult medium for gas exchange. The study explains that tidal ventilation is unusual “owing to the high viscosity, density and low oxygen (O 2 ) concentration of water.” Each of these features makes it harder to move enough oxygen across a respiratory surface, so a water breather needs an efficient way to bring oxygen-rich water to its gills.

The study contrasts tidal breathing with “some unidirectional breathers,” in which water keeps flowing one way. The study notes that most gas-exchange organs of the tidal type “evolved from the invagination of epithelia into pouches with only a single opening, they are tidally ventilated.” A single opening is what makes the water move back out the way it came in.

What the rectal gill is

The gill is built into the hindgut. The study describes the anatomy plainly: the nymphs “have modified the terminal segment of their rectum into a branchial basket, with the rectal wall being elaborated into highly tracheated longitudinal folds.” Those folds project into the basket and form the tracheal gill, which is the surface where oxygen crosses from the water into the body.

The study also places the gill in the wider group of aquatic insect larvae. It says that the nymphs and larvae of several insect orders “breathe water using thin-walled projections of highly tracheated cuticle called tracheal gills.” Dragonfly nymphs use a rectal version of this structure, as described above.

The study explains that tidal ventilation “has two potential limitations,” which it describes in terms of gases equilibrating within the organ and a conducting pathway that adds to the dead space. These limits make the strategy less efficient in one respect, and the study says that tidal ventilation “is less effective in O 2 extraction than other ventilatory schemes” that keep a steadier flow.

How the nymph moves water

The movement is a pumping cycle through the rear opening. The study measured this with a device that records breathing. It notes that the nymphs were “attached to a custom-designed respiro-spirometer to simultaneously measure tidal volume, ventilation frequency and metabolic rate.” These three measures describe the pump: how much water moves each breath, how often the nymph breathes, and how much oxygen the body uses.

The water volume per breath was steady under the conditions tested. The study reports “no significant change in tidal volume” as oxygen fell. The mean tidal volume is given as “60.8 ± 4.5 µl in normoxia,” which means normal oxygen conditions.

The rate changed instead. The study reports that “ventilation frequency increased significantly” as the oxygen concentration dropped. The breathing rate rose from “9.4 ± 1.2 breaths per minute” at 21.3 kPa to “35.6 ± 2.9 BPM at 5.3 kPa” in the most severe hypoxia the study used. So the nymph’s response to low oxygen was to breathe more often, not to move more water in each breath.

How the nymph keeps oxygen uptake

Breathing faster is not the whole story. The study found that the nymphs kept their oxygen extraction efficiency under low oxygen. The authors conclude that “nymphs maintain these extraction efficiencies by increasing gill conductance and/or lowering internal pO 2 to maintain a sufficient diffusion gradient across their respiratory surface.” In this explanation, the gill becomes more permeable, or the internal oxygen level drops, so oxygen keeps moving in.

The study compares these nymphs with other tidal breathers. It states that “Comparison to literature shows that nymphs maintain their OEE during hypoxia unlike other aquatic tidal-breathers and some unidirectional breathers.”

The authors summarise the practical result in one sentence: “dragonfly nymphs, despite breathing water using a tidally-ventilated rectal gill, are well capable of maintaining rates of O 2 uptake in hypoxic conditions, at least temporarily.” The qualifier “at least temporarily” is part of the finding, so the study does not claim the strategy works indefinitely at low oxygen.

How low oxygen fits a wider pattern

Low oxygen is a stress for water-breathing animals, and it can interact with heat. A separate study of aquatic insects states that “Insufficient oxygen has been shown to limit thermal tolerance in several aquatic ectotherms.” That paper compares insect species and finds that “Species that were poor at regulating oxygen uptake were consistently more vulnerable” to warming and low oxygen together.

The aquatic insect paper is not about dragonflies, and its experiments do not measure rectal gills. It is useful here as context: the ability to regulate oxygen uptake is treated as a key trait in how insects cope with stressed water. The dragonfly study supplies the mechanism for one such group, while the wider paper supplies the reason regulation matters.

For a related look at how water plants add oxygen to a pond, see how submerged pond plants add oxygen to water. For how temperature changes the growth of another aquatic insect, see how temperature changes mosquito larval development.

How we chose these sources

We selected two research papers from the PubMed Central archive. The first is a study of oxygen extraction in dragonfly nymphs, and it is the main source for the mechanism. The second is a study of respiratory control in aquatic insects, used only for context on oxygen regulation. Both pages returned HTTP 200 on the check made for this article, and both contain full article text.

What we could not verify

This section lists the parts of the question that the fetched sources do not settle.

What the sources do not say

• The fetched text does not describe how the nymph controls the rectal opening or the muscles that move water, beyond the measured breathing rate and volume.
• The study says the strategy works “at least temporarily” under low oxygen, so the fetched text does not show how long a nymph can keep this up.
• The aquatic insect paper does not study dragonflies or rectal gills, so its results are context only.
• The fetched text does not report the dragonfly species list or how far these results apply to other dragonfly species.

Frequently asked questions

Do dragonfly nymphs breathe through their rear end?

The study describes the gill as a modified rectum. It states that the nymphs “modified the terminal segment of their rectum into a branchial basket.” The water enters and leaves through the rear opening, which is how the gill is ventilated.

What is tidal ventilation?

Tidal ventilation means the water moves in and back out through the same opening. The study says that the nymphs “breathe water using tidal ventilation,” which it calls “a highly unusual strategy in water-breathing animals.”

Do dragonfly nymphs breathe faster when oxygen drops?

Yes. The study reports that “ventilation frequency increased significantly” in low oxygen. The volume per breath did not change significantly, so the increase came from breathing more often.

Can dragonfly nymphs keep getting oxygen when water is low in oxygen?

The study says they can, at least for a time. It reports that the nymphs are “well capable of maintaining rates of O 2 uptake in hypoxic conditions, at least temporarily.” The study did not measure the long-term limit.

Is the rectal gill found in all dragonflies?

The fetched sources do not say. The study focuses on dragonfly nymphs, and the general pattern of tracheal gills it describes covers several aquatic insect groups. This article does not extend the rectal gill to every dragonfly species.

Sources

• Oxygen extraction efficiency of the tidally-ventilated rectal gills of dragonfly nymphs. PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC10806436/ (HTTP 200, opened 2026-10-28)
• Respiratory control in aquatic insects dictates their vulnerability to global warming. PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC3971685/ (HTTP 200, opened 2026-10-28)