Friday, 4 August 2017

Dragonflies 2: Common Darter

Territorial male Common Darter
One of the commonest dragonflies in the UK, especially in the south, is the Common Darter Sympetrum striolatum. One of at least 50 species of Sympetrum, Common Darters have a vast range extending from Western Europe across to Japan, and are often migratory. Other species of Sympetrum are found across the whole northern hemisphere, and in North America they are generally called Meadowhawks.

Unlike the various Hawker dragonflies, Darters hunt from a perch to which they regularly return, behaving in a similar way to Spotted Flycatchers. Except when breeding, they are often found away from the ponds that they usually use, along rides through woods where they often perch on twigs or the tops of shrubs. When away from the water they may occur in large aggregations. At the breeding pools, which are often warm and bare, and may be stagnant or even brackish, males are more territorial.
Mating wheel of Common Darter
One of the most noticeable oddities of the Odonata (the group that contains Dragonflies, Damselflies and their extinct relatives) is the odd way they mate. The most archaic insects such as silverfish reproduce by the male depositing his sperm in a packet called a spermatophore on the ground and leading the female to it. At some point in their evolution odonates switched to the male depositing sperm on the underside of their own bodies and the female then arching her body to pick up the spermatophore from a set of secondary sexual organs. The result is the characteristic wheel position pictured. After mating the male may disengage his claspers which up to that point have been holding the female behind her head, or in other species may retain his hold while the female lays her eggs to avoid the chance of the female mating with another male.
Ovipositing Common Darters
It takes about a year for the naiads to develop, and as with many dragonflies the males take several days to attain breeding colour. Until then they avoid the water and the resident males. The adults emerge from July and can be on the wing into November or even later.
Immature Common Darter
With their vast range Common Darters are not considered threatened by the IUCN, although changes in land use and pesticides may represent local threats. Natural enemies include larger dragonflies, orb web spiders, and especially birds – the Hobby for example is a specialist on dragonflies and other large insects.

(Images of mating and ovipositing from Wikipedia, others my own)

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