15th August 2010 continued- Hover flies

Large numbers of hover flies were noted at Hilbre on 15th, and it will be of interest to record the following comments by observatory member and insect specialist Dr. Gavin Broad verbatum :-
The invasion was of Episyrphus balteatus – often called the Marmalade Hoverfly (left). There were also quite a few of two other species, Syrphus ribesii (below) and Scaeva pyrastri. Both Episyrphus balteatus and Scaeva pyrastri are well known migrants as well as residents. On the East coast there are sometimes huge arrivals of E. balteatus and one year when I was working at Monks Wood they filled the countryside for many miles. I guess ours were probably migrants but it’s interesting that there were a lot of individuals of an ichneumonid, Diplazon laetatorius, which is a parasitoid of E. balteatus (and other hoverflies). It can lay eggs in the egg or young larva of the host hoverfly. That there were so many of the ichneumonid suggests that the hoverflies could have been home-grown (or a mix of a large emergence and an immigrant swarm). Or that the ichneumonids also move along with the hoverflies. The latter would be really interesting.
Keep an eye out for hoverflies!
photos BSB