Damselfly larvae change their hunting tactics when they detect chemical cues from larger dragonfly larvae

07 05 2026

Researchers from the Faculty of Biology, University of Warsaw, investigated how damselfly larvae change their hunting behavior when chemical cues from a larger predator appear in the water. The study shows that predation risk does not necessarily reduce the number of prey consumed, but it can clearly reshape the hunting strategy itself.

In nature, the mere risk of being eaten can change animal behavior. Prey may reduce movement, use refuges more often, or invest energy in other defensive mechanisms. Such responses, however, are not cost-free: they can reduce the time available for foraging or require additional energetic investment. For this reason, they should be activated mainly when the threat is real. In aquatic environments, chemical cues are especially important. These are substances dissolved in water that provide information about the presence, density or state of a predator. In aquatic food webs, the situation can be complex: the damselfly larva Ischnura elegans, which hunts water fleas Daphnia magna, can itself become prey for the larger dragonfly larva Sympetrum sanguineum. It therefore functions as a mesopredator.

The researchers wanted to test whether Ischnura elegans larvae respond differently to different concentrations of chemical cues from a higher-order predator and to information released by a stressed predator. Previous studies suggested that cues indicating predator stress may sometimes suppress prey defensive responses, because such a predator may be less likely to hunt. It was not clear, however, whether a similar mechanism operates in mesopredators and whether it affects their own foraging.

The experiment used damselfly and dragonfly larvae collected from urban water bodies in Warsaw, as well as Daphnia magna from a laboratory culture, which served as prey. The researchers prepared four types of water: a control medium without predator cues, water with a low concentration of predator kairomones, water with a high concentration of these cues, and water with a high concentration of kairomones combined with disturbance cues released by stressed predators. They then recorded the behavior of 30 larvae while hunting in containers with an open arena and a refuge. Instead of measuring only the time spent hiding, they used behavioral network analysis, which allowed them to track how larvae switched between resting, moving, hiding and actively searching for prey.

Fig. Schematic view of the experimental container in which the behavior of a damselfly larva hunting Daphnia was observed. An artificial plant placed in the center served as a refuge, while the surrounding space formed the open arena of the experiment. The figure comes from the discussed publication: Prey Foraging Patterns in a Complex Landscape of Fear, Sysiak et al., 2026.

All treatments containing chemical predator cues changed larval behavior. The animals switched more often between different activities and used the refuge more intensively. Under both low and high kairomone concentrations, the key behaviors were those performed at the refuge element from which larvae could observe prey and make short movements. When disturbance cues from a stressed predator were also added, activity shifted even more strongly toward the safer part of the refuge, including the artificial plant. Despite these behavioral changes, the number of consumed Daphnia did not differ significantly between treatments.

The most interesting result was therefore not how many prey were consumed, but how the larvae achieved that outcome. A similar final number of eaten prey could result from different hunting strategies. Without predator cues, calmer and more evenly distributed behavior was effective. Under perceived threat, short movements from the refuge or quick excursions into the open arena became more important. The number of prey consumed alone therefore did not reveal the full picture of fear-induced behavioral change.

The larvae did not treat disturbance cues from the higher-order predator as information about reduced risk. On the contrary, they responded with greater caution. The authors suggest that this may result from the close relationship between the studied predators and their similar interpretation of danger cues.

The study shows that the effect of fear on foraging is more subtle than a simple measure of prey consumption would suggest. Predation risk may not change hunting success, but it can reorganize the entire behavior of a mesopredator. The article Prey Foraging Patterns in a Complex Landscape of Fear was published in Ecology and Evolution. The authors are Monika Sysiak, MSc, Dr habil. Barbara Pietrzak and Dr habil. Andrzej Mikulski from the Department of Hydrobiology, Institute of Ecology, Faculty of Biology, University of Warsaw. The study was funded by the National Science Centre, Poland, under project 2018/31/N/NZ8/03800.

Cover photo. Sharp Photography, sharpphotography (CC3.0)