What is a distinguishing feature of damselflies?

A distinguishing feature of damselflies is their possession of three gills at the end of their abdomen. This characteristic is significant because it sets damselflies apart from other similar insect groups, like dragonflies, which do not have such specific gill structures. The three gills are typically flat and serve as an adaptation for respiration when these insects are in their larval aquatic stage.

In contrast, dragonfly nymphs have different respiratory adaptations, such as internal gills or labial masks, which contribute to their feeding strategy. Other features mentioned in some options, like hooked prolegs or the ability to construct tubes, are more representative of other insect types, such as caddisflies, and do not apply to damselflies. Thus, the presence of three gills is a clear and defining characteristic unique to damselflies among other insects in similar habitats.