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93 days to go to National Insect Week

Hover flies, leaf-cutter bees and ‘no-see-ums’

In August last year LE contacted me from Shropshire about an insect invasion of her car port. There were seeming thousands of insects, which despite the open construction clustered under the roof and once they died needed shovelling up. The majority of these insects were flies and specifically hover flies which do not usually reach such numbers although there have been reports over the last decade of large populations which have usually associated with large numbers of prey species. A sample was forwarded to me and comprised 11 hoverflies of four species mostly without common names –
  7 male Marmalade flies, Episyrphus balteatus
  1 male and 1 female Scaeva pyrastri
  2 female Parasyrphus punctulatus
  1 male Syrphus ribesii.
The larvae of these hover flies feed on aphids and other small insects on plants and the adults act as pollinators so they are beneficial to gardeners and farmers. There was also 1 male flesh fly, a species of Sarcophaga, probably carnaria, whose larvae feed on carrion or dung and may well have been frequent visitors but probably in low numbers.

NN emailed asking whether I would be able to identify a 'tube' of dried leaves some 8 inches long and half an inch in diameter which fell out of a garden sun parasol when it was taken out for the first time at the end of May. The ends of the 'tube' were sealed, one end with a leaf and the other with a green 'wax'. At first this seemed like a botanical query but when presented with a photograph it became apparent that insects were involved, specifically a leaf-cutter bee. As roses are often chosen by leaf-cutter bees to build their nests it also seemed likely that we could identify the plant. The two most common leaf-cutter bee species are Megachile centucularis and Megachile willughiella and at that time of year the nest would contain pupae with imminent emergence of adults. Whilst the adults normally use leaf pieces to line the cells (cavities) into which they place provisions and then lay an egg, this is usually done inside an already made burrow/hole, in this case the female selected the inside of the parasol. My advice was that despite rose leaves not looking, perhaps, so attractive after a visit by leaf cutter bees, the bees are useful pollinators so I encouraged NN to place the nest in a shady spot and watch to see if any adults emerged. This he has done.

I have had a number of people anxious to know what is biting them even when they cannot see the culprits. There are always a number of possibilities but without an actual specimen it is impossible to say and when it occurs inside the home, I can only advise them to contact specialist pest controllers who can give expert advice on what might be present. There are often indications even if the insects are difficult to locate. These indoor ‘no-see-ums’ are a problem but one query was slightly different - M was concerned that his basement apartment had numerous insects that were crawling everywhere, including over his clothes. The beasts did not bite but their presence worried him, although he knew this concern was perhaps unrealistic. He moved to a new flat, on the 1st floor, and the problem remained. My first thought was book lice, which are very common, getting their name from the habit of feeding on fungi growing on the glue on book bindings in earlier days but are quite happy in a bag of flour. They are visible to the naked eye and whilst populations can build up, they are pretty harmless and cute. However, when M sent me samples, sealed in sellotape, I could find no book lice and could see very little with the naked eye. Under the microscope I could see dust mites (<0.5 mm), almost invisible to the naked eye but after some discussion it turned out that M had been in the jewellery business and had a very good magnifying glass. Problem solved, throw the magnifying glass away and the mites disappear!

Professor Jim Hardie
Director of Science / Entomologist in Residence, 
Royal Entomological Society

Did you know?

Curious courtship

Insects can have interesting mating behaviours including specific calls, movements and gifts.