Spanish investigators have discovered that dragonflies are capable of parthenogenesis, form of asexual reproduction where growth and development of embryos occurs without fertilization by a male. Up until now, dragonflies had been the only insect not considered capable of this type of reproduction.

"We have now confirmed the exception to the rule. In all other insects, from butterflies to beetles and flies, at least one case of parthenogenesis had been found", said Adolfo Cordero, a biologist from the University of Vigo and worldwide authority on dragonflies.

The discovery was made during a series of visits by Cordero and his team to the Azores, a group of nine islands that lie in the Atlantic, some 1500km off the coast of Portgual.

The group took larva samples of the Ishnura hastata species of dragonfly, which they already suspected of living in communities made up entirely of females, and bred them in their lab, producing nine generations of dragonflies, 2000 female infant insects in total.

This species of dragonfly, which surprisingly reproduces in a "normal" way everywhere else in the world, is found on eight of the nine islands that make up the Azores archipelago. The only island it is not found is La Graciosa, where there is hardly any fresh water.

Cordero has just started collaborating on a project with the San Francisco University in Quito to find out if the same thing occurs with these dragonflies on the Galápagos islands. This particular species of dragonfly is found from southern Canada down to southern Colombia and is relatively common in the Caribbean islands too.

The scientists do not know if the dragonfly arrived in the Azores already able to reproduce this way, or whether it has evolved the ability in the absence of male members of the species since its colonisation of the Azores.