Apparently it is summer, although our atmosphere doesn’t seem to agree; this damp grey-ness might well be the new normal as a result of climate change so don’t get your hopes up that it will be better next year. Anyway, summer is a time for insects and some of the most eye-catching and interesting of all are the Odonata – dragonflies and damselflies – most of which are on the wing from May through to October.
I was walking on Ashdown forest a few weeks ago in bright sunshine (that was our summer) when I came across a peaty pool fed by a wee brook in a valley. At the far end of this pool were two large dragonflies, whizzing around at great speed and clattering into each other with a crackle of wings as they seemingly jousted for territory. They were a little too far off to identify confidently, though I suspected what they were, however a little farther on the walk I came across several more coffee-coloured ponds. Parading around each pond were more dragonflies – with fat blue abdomens, clinching them as Broad-bodied Chasers Libellula depressa. Being Chasers they sat obligingly on rush stems and darted out over the water at regular intervals; whilst perched I could see the beautiful intricacy of these insects bodies and wings – marvels of engineering that are more like mechanical models than real living organisms.
- Libellula the genus name rather boringly just means ‘dragonfly’ but the specific name ‘depressa’ refers to the shape of the adults abdomen which is fat when seen from above but side-on is rather skinny.
- Males and females look nearly identical when first emerged, both sporting golden-brown abdomens with yellow spots on the side, however the males quickly develop a bright powdery-blue ‘pruinescence’.
- Broad-bodied Chasers can easily be told apart from other chasers by their fat bodies with yellow spots on the side and the dark triangular-patch at the base of each wing.
- The larvae are also rather bulky looking and spend 1-3 years underwater feeding on other larvae, water insects, tadpoles or even small fish which they catch with extendable grasping mouth parts.
- Adults can be seen on the wing from May through to August, peaking in June, they can often be found far from water as they sometimes migrate great distances in search of new territory.
- They have a distinctive behaviour which separates them from hawkers; they will sit on a perch (usually a water-side plant stem) scanning the sky for passing insects, on spotting one they will shoot off to inspect it and then either catch and eat it, chase it off if it is a rival male or mate with it if a female, they then return to the perch.
- This species has a range covering most of Europe, central Asia and the Middle East. In Britain it is found throughout southern and central England and Wales but is absent from the north.
- The colouring of the females has been suggested to be a form of Batesian mimicry; the yellow patches, broad abdomen and golden colour seem to resemble a hornet which it can be mistaken for at a distance – predators (mainly birds) tend to focus on colours and patterns so the great size difference is not a problem.