Lord Campbell of Croy:
"My Lords, can my noble friend assure us that this fly, which sounds most pernicious, is neither a threatened nor a protected species?"

The Earl of Dundee:
"No, my Lords, the fewer the better."

The 'most pernicious' fly in question is the Blandford Fly, otherwise known as Simulium posticatum, which is only one of the thousand or more species of blackflies that belong to the taxonomic family Simuliidae. It is one of the forty or so such species that inhabit the British Isles and can be found across south-east England in "an arc running from East Anglia, through Oxfordshire to Dorset", with a particular concentration along the banks of the river Stour and is named after the town of Blandford Forum in Dorset which lies on that very river.

Each summer the female of the species lays its eggs in cracks high up above the water level on the steep and shady banks of the Stour river. There the eggs lie in a state of dormancy until the first spell of cold weather triggers the further development of the larvae within the eggs. By February, they are fully developed and await the arrival of the winter rains which causes the river level to rise, flooding the cracks and hatching out the eggs.

The hatched larvae swim out into the river and anchor themselves by a silken thread to a piece of vegetation on the river bed and proceed to feed on algae, bacteria and whatever bits and pieces pass by in the fast flowing river. After about eight weeks the larvae bein to pupate, and as it does so the larva spins a little silk pocket, so that when the pupa hatches a few days later it emerges inside its own little bubble of air which transports the fly to the water surface, allowing to immediately take to the air.

As a result during the months of May and June large numbers of the male flies gather together in huge swarms awaiting the arrival of the females. As with most blackfly species the female prefer to have a meal of blood to provide the necessary nutrition in order to bring their clutch of between 200 and 300 eggs to maturity. Each different blackfly species tends to have its own preferred host; in the case of the Blandford Fly, and herein lies the rub, their preference is for homo sapiens.

Thus during the 'biting season' which runs from early May through to the first week or two of July, thousands upon thousands of female Blandford Fly zoom about around a foot off the ground trying to satisfy their craving for human blood, biting into the nearest expanse of exposed leg they come across. Victims are said to experience a "painful stabbing sensation" whilst the fly's saliva enters the wound and causes "severe irritation, pain, swelling and blistering". The bites can cause serious lesions and there have been reports of arthritic reactions, although whether this is as a result of infection or allergy is uncertain.

The Blandford Fly is therefore classified as a 'nuisance species', in the same league as the Scottish Birch Fly, or Simulium reptans sometimes known as the 'super midge' which plagues Speyside in a similar fashion. Neither of which however is that serious a threat to life and limb, in contrast to their cousin Simulium damnosum, prevalent in Africa, which carries the parasitic worm Onchocerca volvulus, and is responsible for the onset of onchocerciasis otherwise known as 'river blindness' in its victims.

Neverthless for many years the Blandford Fly has emerged every May and plagued the good citizens of the towns and villages of the Stour valley. Naturally the call came for the authorities to 'do something' about the problem and eventually in 1972 Dorset County Council sought the assistance of the Freshwater Biological Association who commissioned one Robert Hansford to carry out a detail study of the fly. His extensive research suggested a number of ways in which the fly population might be controlled, many of which were tried, but none of which appeared to have any effect on the numbers which emerged each summer to nibble away at human flesh just as before.

It was not until the 1980s that the Centre for Ecology and Hydrology suggested that a newly discovered bacterium from the Negev desert in Israel, Bacillus thuringiensis var Israelensis, might prove to be a solution to the problem. This bacterium produces spores which contain certain enzymes which, when eaten by the larvae of the Blandford Fly, destroy their gut walls, leading to the rapid demise of said larvae. What was important about this proposed biological treatment was not so much that it killed the larvae of the Blandford Fly, but that it did not kill the larvae of any other species of blackfly. There being of course, a wide range of creatures who feed upon blackflies and their larvae, and it would generally be regarded as a bad idea to wipe out an entire ecosystem just to save a few people from getting bitten every year.

So in 1989 a trial treatment was carried out on a test area on the river which confirmed the theory and in 1991 the first large scale treatment of the river took place. This appears to have had the desired effect; whereas there were some 1,400 reported cases of individuals seeking treatment for fly bites in 1988 this had reduced to just 45 in 1999. According to Mike Ladle, a Fellow of the Freshwater Biological Association, "this is probably the best example of the use of a biological agent to control a pest, in an ecologically friendly fashion, anywhere in the world".

The independent brewers Badger Ales which is based at Blandford St Mary in Dorset (just to the south and on the opposite bank of the river Stour to Blandford Forum) brews a Blandford Fly Ale which is described as a "light coloured medium bodied ale with a low bitterness". Its main claim to fame is that it is flavoured with ginger, based on the local folklore which suggested ginger as a treatment for the bite of the Blandford Fly.


  • From a Press Release by North Dorset County Council - Blandford Fly Bites Minimised Following River Treatment dated 27 May 2004 and the attached article The Blandford Fly by Mike Ladle PhD. Fellow of the Freshwater Biological Association.
  • The Blandford Fly at
  • Onchocerciasis www.icp.ucl.ac.be/~opperd/parasites/onch1.html
  • Beware the 'Super Midge' http://www.mountaineering-scotland.org.uk/nl/54f.html
  • T. D. Healing, Arthropod Pests as Disease Vectors a paper delivered at the International Conference on Insect Pests in the Urban Environment at Cambridge University in 1993 See
    www.killgerm.com/downloads/Arthopods%201,%202%20&%203.pdf? http://lists.foodsafetyweb.info/SCRIPTS/WA-FOODSWS.EXE?A2=ind9911&L=foodsafe&P=21948