How Do Dragonfly Larvae Capture Prey With a Labium?

As an Amazon Associate we earn from qualifying purchases.

How do dragonfly larvae capture prey with a labium? The answer is a mouthpart that is modified into a prehensile mask for capturing fast-moving prey. The labium is extended forward during the predatory strike, and its paired palpi open to grasp the target. High-speed recordings show how quickly the whole movement happens, and the morphology of the mouthpart shows how it is built. This article explains the strike, the structures involved, and the parts of the process the research has not yet settled.

Quick answer

• The predatory strike uses the labium, which one study describes as a modified underlip that works as a protractile organ.
• In globe skimmer nymphs, full labial extension during capture took 63 ± 24 ms.
• The labium has sensory structures, which the study describes as additional sensory organs that serve some functionality.
• The energy behind the strike comes from earlier work, and the trigger mechanism is still a hypothesis.

What the labium is

The labium is an unusual structure. One study notes that dragonfly nymphs are among the only insects or animals known to have a modified underlip used as a protractile organ, which the study refers to as a labium. That is the feature that lets the mouthpart be pushed out toward prey.

The mouthparts of dragonfly nymphs include the extendable labium, mandibles, labrum, maxillae and hypopharynx. The study focuses on the labium and the mandibles, which serve important functions such as capturing the prey and cutting it. The labium is therefore the part that reaches out, and the mandibles deal with the prey after it is caught.

The labium itself has three main parts. The prey-capturing labium constitutes a postmentum, a prementum and labial palpi, which are connected to the prementum by articulation joints. The palpi are the parts that open around the prey. The joints are what allow the palpi to move forward with the rest of the structure.

How the strike happens

The strike follows a clear sequence. This involves a gradual opening up of the two cup-shaped labial palpi and moving them forward with the help of unfolding prementum and postmentum parts. The study compares this movement to the extension of human arms with the elbow and shoulder joints.

The timing is fast. In the study, the time taken for the protraction and retraction of the labium during prey capture was estimated to be 187 ± 54 ms, which the authors read as a sign that the nymphs have a rapid prey mechanism. A separate figure from the same study puts the time for full labial extension during capture at 63 ± 24 ms.

The study recorded the nymphs under water using high-speed photography, which allowed the protraction and retraction to be observed in detail. The images show the change in angle of the prementum and postmentum of the labium, and the opening of the labial palpi as the prey is captured. These frames are the basis for the timing figures above.

Earlier work has offered explanations for the energy behind the strike. One mechanism described in that work is the release of energy stored by strong contraction of the abdomen and thorax muscles. The study presents this as an earlier finding, not as something it measured directly in the globe skimmer nymphs.

The trigger for the strike is less certain. The study notes that the labium protraction was hypothesized to be initiated based on a click mechanism at the prementum and postmentum joint that disengages to release energy. The word hypothesized is the study’s own, which signals that the click mechanism is a proposal rather than a settled result.

Why the sensory structures matter

The labium is not only a grasping tool. The morphological details suggest that the prey-capturing labium is a complex grasping mechanism with additional sensory organs that serve some functionality. That phrasing is the study’s own, and it marks the sensory role as partly described rather than fully mapped.

The study reports sensillae on the labial palpi. Scanning electron micrographs in the study show the sensillae in pairs along the line of contact of the two halves of each palpus. The same images label the joints that move the palpi during prey capture, which are the points where the sensory and mechanical parts meet.

The study also describes setae on the labium and its palpi, and its images mark these hairs alongside the joints. The images place the setae and the sensillae on the same structure, which is useful for a reader trying to picture the mouthpart. The sources do not go further than this description.

How prey choice works

Capturing prey is only part of the story. A second study looks at which prey dragonfly larvae choose. Despite a long tradition of research, the authors say, understanding of the mechanisms driving prey selectivity in predatory insects is limited. That study used larvae of Sympetrum sanguineum, which is a different genus from the globe skimmer used in the capture study.

The study explains the general logic of prey choice. According to optimal foraging theory, predators should prefer prey which provides the highest amount of energy per unit time. However, the study notes that prey selectivity may also depend on previous diet and on the specific nutritional demands of the predator. A larva’s choices therefore reflect more than the energy value of a single meal.

The experiments were built around conditioning. The authors conditioned the larvae to one of two prey types and then exposed them to various combinations of the two prey types. Larvae conditioned to Chironomus larvae consumed significantly fewer Chironomus larvae than larvae conditioned to Daphnia magna, although they ate the same amount of Daphnia magna.

The capture result is the part most relevant to the labium. The study reports that there was no effect of previous diet on the success of capture and handling time. It connects this to a limited role of learning in the ability to process prey, which means the capture process itself was not shown to change with earlier diet.

The survival and growth data add another layer. The study tested diets with different proportions of the two prey types. It reports that larvae fed a mixed diet had the highest survival and growth rate. In the authors’ conclusion, dragonfly larvae fed by Chironomus larvae performed poorly and compensated by preferring Daphnia magna.

What we could not verify

What the sources do not say

The two studies do not describe the same species. The strike was measured in globe skimmer nymphs, while the prey-choice work used Sympetrum sanguineum larvae. The sources do not show that the two species strike in the same way. The sources also do not give a range for how often a larva misses its target, and they do not address how the labium behaves in a garden pond.

How we chose

Both sources are open-access research articles hosted on PubMed Central. Each URL returned HTTP 200 on a direct request on 2026-10-28, and each page contained article text. The statements above were checked against the fetched text, and each claim maps to a sentence in one of the two papers.

Frequently asked questions

What is a labium in a dragonfly larva?

The study describes the labium as a modified underlip that is used as a protractile organ, which is referred to as a labium. It sits among the mouthparts, alongside the mandibles, labrum, maxillae and hypopharynx.

How fast does the labium move during a strike?

In the globe skimmer study, the protraction and retraction of the labium during prey capture was estimated at 187 ± 54 ms. Full labial extension during capture was measured at 63 ± 24 ms.

Do dragonfly larvae learn how to catch prey?

The prey-choice study reports that previous diet had no effect on the success of capture and handling time. It connects this to a limited role of learning in the ability to process prey.

What kind of prey do dragonfly larvae prefer?

The sources describe prey selection as tied to energy and nutrition. Optimal foraging theory predicts a preference for the highest energy per unit time, but prey selectivity may also depend on previous diet and nutritional demands.

Why does the labium need sensory structures?

The morphological details suggest that the labium is a complex grasping mechanism with additional sensory organs that serve some functionality. The study shows sensillae on the palpi, but the sources leave their exact role open.

For the way these larvae breathe in the water, see how dragonfly nymphs breathe underwater. For the adult insect’s flight, see how dragonflies fly with four independent wings.

Sources

• Prey Capturing Dynamics and Nanomechanically Graded Cutting Apparatus of Dragonfly Nymph. PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC7865395/
• Prey selectivity and the effect of diet on growth and development of a dragonfly, Sympetrum sanguineum. PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC6839516/