Ischnura elegans | Blue-tailed Damselfly

Introduction

The Blue-tailed Damselfly (Ischnura elegans) is one of the commonest and most widespread damselflies of Europe, a small, slender insect of ponds, lakes, canals and slow rivers that can be seen from late spring through summer. Males are powder-blue with a striking blue band on the final segments of the abdomen, while females come in several colour forms—blue, violet or greenish—which makes the species look more variable than it is. Tolerant and adaptable, it is often the damselfly that turns up in the smallest garden pond, and it is an excellent beginner’s species for anyone learning the group.

Taxonomy

Ischnura elegans belongs to the family Coenagrionidae, the narrow-winged damselflies, and is one of several similar small species in its genus. It is told from its relatives by the broad blue “tail light” on the tip of the abdomen and by the pattern of the thoracic stripes. It shares waters with the larger dragonfly fauna, including the Emperor Dragonfly, though it stays low among the stems while the dragons patrol overhead. No subspecies are widely recognised across its European range, but the female colour forms have long interested naturalists.

Physical Characteristics

Adults are small, with a body length of about 3 to 3.5 centimetres and a wingspan near 4 centimetres. The wings are clear and narrow, held together above the body when at rest. Males are pale blue on the thorax and abdomen, marked with black bands and a conspicuous broad blue segment near the tip; females vary from blue to violet to olive-green, all with the dark wing spots and a pale wing base. The eyes are blue-green in males and duller in females, and the legs are black. Freshly emerged adults are pale before the colours deepen over a day or two.

Habitat

Blue-tailed damselflies use still or slow fresh water of almost any size, from tiny garden ponds to lakes, canals, ditches and gently flowing rivers with plentiful emergent vegetation. They need upright stems—reeds, rushes, sedges, iris—on which to perch, mate and lay eggs, and they tolerate shade and mild disturbance better than many species. They meet the European Pond Turtle and the Common Frog at the same weedy margins, sharing the healthy pond edge with a wide freshwater community.

Diet

Adults prey on small flying insects—midges, gnats, aphids and tiny flies—taken in short darts from a perch or in slow handling flight just above the water. They are useful predators of nuisance insects around ponds. The larvae are aquatic hunters of water fleas, mosquito larvae and other small invertebrates, lurking among pond weeds. Both stages link the underwater nursery to the air above, feeding and being fed upon within the pond ecosystem, and the species helps keep the water’s invertebrate life in balance.

Reproduction

Mating follows the typical damselfly tandem: the male clasps the female behind the head and the pair form a heart-shaped “wheel” as she curves her abdomen to receive sperm. They then fly to waterside plants, where the female slits open soft stems and inserts eggs underwater, often with the male still guarding. The larvae live among pond vegetation for several weeks to a few months before climbing a stem to moult into the adult. There is no care after egg-laying, and the adults live only a few weeks through the summer.

Conservation

The blue-tailed damselfly is abundant and rated Least Concern across its range. Its adaptability—using garden ponds, canals and even brackish ditches—means it is less threatened than specialist species, but it still suffers where ponds are filled in, heavily stocked with fish that eat the larvae, or smothered by pollution. It benefits from leaving marginal vegetation un-cut, from creating new ponds, and from reducing pesticide runoff. Because it is so common and visible, it is a handy, everyday indicator that a pond still supports a healthy aquatic community.

Fun Facts

• Females occur in several colour forms: blue, violet and greenish.
• The male’s bright blue “tail light” gives the species its name.
• The mating pair forms a neat heart-shaped wheel in the air.
• It is one of the few damselflies happy in tiny garden ponds.
• It rests with its wings pressed straight together above its back.