Friday, 9 November 2012

Flies of an Indian Summer

The last three or four days have been remarkably bright and dry so, despite a chill in the air, I sallied forth to investigate local patches of ivy for diptera -plus whatever else might be about.

In fact rather low temperatures had not deterred insects to any obvious extent. Along one south-facing hedgerow in Byfield Pocket Park (SP518529) the ivy flowers were being visited by specimens of the Common Wasp Vespula vulgaris and even Honey Bees Apis mellifera. There were also a couple of specimens of the Green Shield Bug Palomena prasina, though these were on the foliage and not interested in the nectar riches. The shield bugs were already turning from their bright green summer coloration to a dingy brown and, with this camouflage to provide protection, they will creep beneath dead leaves to overwinter. These bugs have few predators - their foul taste deters most creatures - but one pretty tachinid fly, Subclytia rotundiventris, is known to parasitise them. Another group of tachinids, Phasia species, are also known to be parasites of shieldbugs but most records are from continental Europe.

The ivy flowers were besieged by diptera; my specimens will stay in the fridge to be dealt with later. However, on November 5th one instantly recognisable fly was represented by at least three specimens; this was the Noon Fly Mesembrina meridiana, an insect which I associate with high summer. With its glossy black body and bright orange wing-bases this must be one of our smartest insects. According to D'Assis Fonseca it occurs up to September, so this is a remarkably late record.

So, it isn't just winter gnats providing interest through the winter months. There may yet be surprises.


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