Damselfly (Zygoptera): appearance, life cycle, behaviour and distribution

Anatomy and identification

Damselflies have two pairs of membranous wings, a long slender abdomen and large compound eyes that are widely separated on the head. Unlike many dragonflies, the forewings and hindwings of damselflies are similar in shape and venation. When at rest many species hold their wings folded together over, or along, the body; however, a few families rest with the wings spread. Adults have legs adapted for perching and seizing prey but are not built for walking across surfaces.

• Size and form: generally smaller and more delicate than dragonflies.
• Eyes: clearly separated on the sides of the head.
• Wings at rest: often closed together above the abdomen, though exceptions exist.
• Colour: ranges from metallic blues and greens to dull browns; sexual dimorphism is common.

Life cycle and development

Damselflies undergo hemimetabolous development (incomplete metamorphosis). Eggs are typically laid on or near plants in or beside water. The aquatic stage is an essential part of the life cycle, during which the immature form—called a nymph or naiad—lives in freshwater habitats. Nymphs breathe through internal or external gills and are active predators of other aquatic invertebrates. After several moults the nymph climbs out of the water and completes a final moult to emerge as a winged adult.

1. Egg: deposited on submerged or emergent plants, or on damp substrates.
2. Nymph: aquatic and predatory, growing through successive instars.
3. Emergence (eclosion): final moult from nymph to adult.
4. Adult: aerial stage focused on dispersal, feeding and reproduction, usually near water.

Habitat, feeding and behaviour

Damselfly nymphs live in a variety of freshwater habitats including ponds, lakes, slow-moving streams and marshes. The adjective aquatic applies to their immature stages. Both nymphs and adults are carnivorous: nymphs eat aquatic invertebrates and small tadpoles or fish fry when large enough, while adults catch flying insects on the wing. Many species display territorial behaviour in males, perch regularly, and perform courtship flights or displays prior to mating.

Adults frequently stay close to the water where they hatched, forming loose aggregations or roosting in vegetation. Their vision is adapted to detect movement, and their rapid take-off helps them avoid predators despite their bright coloration.

Distribution, diversity and evolution

Damselflies have a long fossil record, with relatives traceable to the late Carboniferous period in some interpretations. Modern damselflies are grouped in about twenty families and many hundreds of genera and species worldwide. They occur on every continent except Antarctica; see resources on their geographic distribution for regional lists and guides. Different families are adapted to particular habitats: some prefer running waters, others still waters, and a few occupy unusual habitats such as temporary pools or brackish marshes.

Ecological role and conservation

Damselflies are important both as predators and as prey. Nymphs help control populations of aquatic invertebrates and are themselves eaten by fish and amphibians. Adults form part of the diet of birds, spiders and larger insects. Because nymphs require good water quality and suitable aquatic vegetation, damselflies are widely used as indicators of freshwater ecosystem health. Habitat loss, pollution, invasive species and changes in hydrology can reduce local populations; conservation of riparian zones and water quality supports damselfly diversity.

Distinguishing damselflies from dragonflies

Key differences include eye placement (separate in damselflies, commonly touching or closely set in many dragonflies), wing shape and venation differences, and typical wing posture at rest. Flight style also differs: dragonflies often fly faster and with greater agility, while damselflies are more fluttering and may remain closer to vegetation.

Further information, identification keys and regional field guides are available from entomological texts and conservation organisations; for general overviews consult sources on insects, the order Odonata, and specialist treatments of dragonflies and damselflies. For summaries of the life cycle and aquatic ecology of odonates, and for explanations of terms such as nymph, see introductory materials and regional guides.