Late Season Flies

Tony White has sent me the following article on cluster flies and ivy. I remember when I worked for what is now Tata Steel Europe in Corby that at this time of the year my office and other offices at the corners of the building were plagued by hundreds of cluster flies Pollenia rudis as these flies emerged from the surrounding grassland and sought overwintering quarters in the spaces above the false ceilings.

 Ivy flowers and Pollenia species

Shelley reminds us that “The yellow bees in the ivy bloom” (Prometheus Unbound), but there are lots of diptera to interest us too, with ivy's nectar providing the last great feast of the year for many species.

Prominent among these are species of Pollenia and an excellent online key is to be found by looking for “Cluster Flies of North America”. Although it is a key to Canadian species it covers all British species with the exception of Pollenia amentaria and P. viatica (the latter species being easily recognised by its almost-black abdomen). Using this key I have been able to record Pollenia angustigena

and P. pediculata from ivy in the Byfield area (as well as the ubiquitous P. rudis) and it seems likely that these species are quite widespread and much under-recorded.

Now where can I find a reliable key to Calliphora species!

Tony White

Some of last week's flies.
 

On Thursday morning I was at Grendon Lakes and noted large numbers of muscid flies sitting on tree trunks and foliage in full sunshine. They were very wary but I obtained three as a sample. They keyed out to be the common muscid Muscina levida, all males. I am not sure whether these were mating swarms or just a plentiful fly finding opportunities to warm up. Several Eristalis hoverflies were visiting ivy and on the few hogweed plants that were still in flower some other species were present. The most notable of these were Cheilosia soror but I also found a solitary Platycheirus that keyed out to P. splendidus. This species is primarily a Spring species and the specimen I took was a female, so it might be P. scutatus. This latter species is much more frequent in the Autumn and females of this group are only dubiously separable, so maybe it is better recorded under the aggregate name. At the same site, Jeff Blincow showed me an elongate bright metallic green soldierfly, which was the Autumn-flying Sargus bipunctatus.

Leaf Mines

Autumn is a good time to look for leaf mines. A number of groups of insect have larval stages that feed in leaves, leaving a characteristic trail. As many leaf miners are specific to one or few species of plant, it is often possible to identify the insect from the pattern of the mine and the species of plant. These websites are useful guides to identifying leaf mines.

http://www.leafmines.co.uk/index.htm

http://www.ukflymines.co.uk/index.php

Amongst the flies, the family Agromyzidae is the main group that make leaf  mines. Some hoverflies 
also have leaf mining larvae. Notably Cheilosia caerulescens is a miner of house leeks Sempervivum. 
It has not yet been recorded in Northants but has been found in Bedfordshire. Look out for mined 
leaves of house leeks. Visits to garden centres may be productive as it is thought that the fly entered
Britain in imported plants.

When the weather is not suitable for finding adult flies, looking at leaf mines is a good way of 
recording species. Last week I found Agromyza filipenduli on meadowsweet, Liriomyza eupatorii
and Phytomyza eupatorii on hemp agrimony and Agromyza alnivora on alder leaves at Yardley
Chase.

Phytomyza eupatorii leaf mine on Hemp Agrimony

 Agromyza alnivora leaf mine on Alder

Agromyza alnivora leaf mine on Alder. The larva is visible as a small dark object at the top of the mine (not
the larger brown blotch)

Late Summer Diptera

Towards the end of the Summer, the weather has been more conducive to hoverflies. In particular there have been very good numbers of Eristalis species visiting plants such as Wild Angelica, Wild Carrot and Hemp Agrimony. As the Ivy comes into flower this too attracts a lot of species.

Eristalis species visiting Wild Angelica near Yardley Hastings.


I have had several reports of Volucella inanis and a couple of reports of the even larger hornet mimic Volucella zonaria in Northampton.

Volucella inanis at Boddington Meadow Nature Reserve.

The hoverfly Rhingia rostrata has recently colonised many parts of Northants. It tends to be more frequent in Autumn, although I did note it a couple of times in the Spring. It can be separated from the more common Rhingia campestris by having all-yellow legs and no black edges to the abdominal segments.

Rhingia rostrata at Rothwell Gullet Nature Reserve.

Autumn also brings out a number of cranefly species. The most prominent is the long-palped cranefly Tipula paludosa. This can emerge in large numbers from damp grasslands and frequently enters houses.

Tipula paludosa at Rothwell Gullet Nature Reserve.

Restarting the blog

I am afraid I forgot all about the blog and it was only seeing the excellent Northamptonshire Birds blog run by Neil and Eleanor McMahon that reminded me. Anyway I intend to get it going again so if you have any Diptera news or photos do let me know.

This year has been very poor for Diptera but the past couple of weeks or so have seen something of an improvement and maybe the season will turn out to be interesting. Particularly notable are the large numbers of hoverflies visiting umbellifers, especially wild angelica and wild carrot. Many of these are Eristalis species, mainly E. pertinax and E. arbustorum but the other common species are present if you look carefully. In my garden, marjoram is also attracting a lot of hoverflies at present. At least 10 species of Hoverfly have been around over the weekend. Also in my garden I have been invaded by the weed Soapwort Saponaria officianalis. It is a nightmare to control. However it has added a new fly record to my garden list as its leaves are mined by the Agromyzid fly Amauromyza flavifrons.