Pronged clubtail  (Gomphus graslinii)

Classified as Near Threatened (NT) on the IUCN Red List 2007 (1), and listed on Annex II of the Bern Convention and on Annex II and IV of the EU Habitats Directive (2) (3) (4).

This colourful dragonfly is a typical member of the Gomphidae family, commonly known as ‘clubtail dragonflies' for the enlarged area at the tip of their abdomen. Like many other members of this distinctive family, this species possesses light green to yellow colouration with black stripes, and widely separated eyes (2) (3) (5).

Known primarily from south-western France, but also from the Iberian Peninsula (Spain and Portugal) (1) (2) (3).

The pronged clubtail is found in and around large rivers in hilly landscape with slow-flowing sections, and also in brooks up to 400 metres above sea level. The damming of rivers creates slow-flowing sections, favoured by the pronged clubtail (1) (2) (3).

Odonata species start their life as aquatic larvae, passing through a series of developmental stages or ‘stadia’ and undergoing several moults as they grow. Before the final moult (emergence), metamorphosis occurs in which the larvae transform into the adult form. Adults complete their metamorphosis after emergence and undergo a pre-reproductive phase known as the maturation period, when individuals normally develop their full adult colour (3) (6). Virtually nothing has been published on the pronged clubtail’s social, reproductive or feeding behaviour, but certain details can be inferred from what is known about related species in the same habitats and climatic areas. Eggs should hatch 10 to 60 days after deposition and the larval period should spread over two to three years, passing through 11 to 15 stadia. The larvae hunt hidden within the sand or leaf litter detritus at the surface of the sediments. Emergence is rapid, and the adult flight period for the pronged clubtail lasts from June to the beginning of September (2) (3) (7).

Most of European Gomphid species don't defend territories and are easily observed on the ground or perched in the vegetation. In the pronged clubtail, a fairly low aggressiveness is obvious between males. Females lay eggs alone, not being guarded by their mate, touching water by the tip of their abdomen during a typical confused flight, so that eggs will detach easily and fall to the bottom of the river, where a mucus envelope fixes them to the substrate (8) .

Adult Odonata feed on flying insects and are often generalised, opportunistic feeders, sometimes congregating around abundant prey sources such as swarms of other insects (6).

This clubtail dragonfly is threatened by water pollution, changes to stream structure, and summer droughts. Summer droughts have become increasingly frequent and severe in recent years, drying up many streams and rivers in some areas, and leading to an associated rise in pollution of the remaining waterways (1).

There is a need to preserve water quality throughout this species’ range (1).