Sunday, July 3, 2011

The island bluetail damselfly

Island bluetail damselfly (Ischnura genei)
The island bluetail damselfly is a delicate insect known in Maltese as damigella. It is closely related to the more robust dragonflies. 

It lives in valleys with running water and near ponds, pools and reservoirs. 

It is a weak flyer and does not stray too far from aquatic habitats on which it depends throughout its life cycle. Like dragonflies the damselfly lays its eggs in water. The larva spends its entire life under water feeding on smaller organisms.

Two forms of this species are found in two colour forms: green and reddish-brown. Both forms can occur in a particular place and the colour might a result of different environmental temperature during the larval stage of the damselfly. 

In other insect species larvae that are developing later in the season, when the temperature is higher give rise to brown adults which are thus better camouflaged in the dry summer vegetation. As far as I know this has not been investigated in damselflies but a future study might show such a link.

Like dragonflies, it has very interesting courtship and mating habits, quite different from that of other insects.

The genital opening is near the tip of the tail, but before mating the male transfers his sperm to an accessory genital organ on the underside of his abdomen, just behind the thorax. 

He then finds a female and seizes her by the neck with a pair of claspers situated at the hind end of his body. They then fly in tandem and settle, linked together in this way.

When mating takes place, the female bends her body around under the male’s body and the sperm is transferred for fertilization.

Damselflies and dragonflies use different methods to lay eggs. Some insert them in the plants of aquatic plants or in vegetation at the water’s edge. 

Others fly over the water and drop them, while others dip the abdomen into the water to wash the eggs off the tip. Some species remain in tandem whilst the female is laying.

Their larvae or nymphs spend all their time under water hunting smaller animals. A hunting larva stalks its prey to within a centimetre or less, than shoots out the labium and seizes its prey with its claws. 

The victims are mostly insects, but large well-grown larvae can even catch tadpoles and small fish. The labium is a segmented organ, found in all insects below the mouth. In dragonfly larvae this organ bears a pair of pincer-like jaws near the tip and is elongated and hinged so that it can be extended in front of the head.

This article was published in The Times on 20.04.2011

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