Back to work today, and as I was walking round to the gatehouse, I found this blackfly on the galvanised fence. Nothing unusual about that, except for the size – this fly is about a centimetre from nose to wingtip, positively majestic for an aphid!
I submitted an ID request to the Yahoo BugClub forum and got a great reply from the one they call ‘Mark’:
This is the large Willow Aphid - Tuberolachnus salignus Possibly the largest of the aphids in the world. It has had a sudden increase in numbers in the last few years.
He also included a link to the NatureSpot web site at www.naturespot.org.uk, which had this to say, in part:
Giant Willow Aphids are dark brown with a peppering of black spots but can appear grey from a white dust which forms on them. It is an unusually large aphid, measuring up to 6mm long. Adults of the species have a thorn-like tubercle which protrudes from its back. As with other species of aphid, some giant willow aphids are winged; an adaptation believed to emerge in reaction to environmental pressures. Found primarily in large colonies on the trunks and branches of willow and sallow trees, the aphids splay their back legs and kick in response to potential threats.
Although most common in the summer, this species can be seen in most months of the year, sometimes persisting into the winter. Giant willow aphids appear to reproduce entirely asexually. Thought to be widespread and fairly frequent in southern Britain at least.