Blandford Fly

I've just had the following enquiry (paraphrased for brevity from an email from OUMNH) and I'd grateful for replies/comments to any of the points raised; and/or perhaps a trustworthy reference that can help.

Thanks , Ivan  

I've just suffered my first Blandford Fly bite of the season. These insects are a plague here in NW Oxfordshire, and susceptible being fairly near a body of water.  They seem to be striking earlier than usual this year – from memory, May is more typical.

I know their range tends to follow the Jurassic outcrop from Blandford Dorset out to the coast in East Anglia – but I'm not sure what the width of their pathway is?  Do they attack people in Oxford, for example?

I've tried all sorts of repellents, but haven't yet found anything that seems to work.  Do you have any suggestions?

What is the lifecycle of these pests? Do you know why these bites raise such a huge reaction in some.  Who might be particularly susceptible and why? And is there any mileage in seemingly crank advice, like eat marmite?


Hi Ivan, can't help with any personal knowledge I'm afraid, but just in case you haven't already discovered it there's some background information here:

The repellant that works best for me is Smidge, which seems to deter a range of biting insects but I don't know whether it works on blackflies specifically.


Hi Ivan,

The fly you are talking about is Simulium posticatum. It is called the Blandford fly because it is a minor public health problem in Dorset where there are many clinical reports of reactions to the bite of this blackfly that does not really occur with other Simulium in the UK. It is also called the Stonesfield stinger or Woodstock fly in Oxfordshire, which is the only other area where bites are a problem.

Like other Simulium the larvae and pupae can be found in flowing water only, the larvae attaching to rocks, stones or trailing vegetation to feed on microscopic organisms and particles in the water - attempts have been made to try to control the larvae in streams and rivers using insecticides (on particles) or the bacillus BTI (granular).

The distribution is limited, Crosskey & Crosskey ( 2002, Dipt Digest 9, 25-60) in their fantastic and comprehensive survey of SE England found it in Dorset, Oxfordshire (around Oxford, R. Cherwell and R Thame, see also Williams 1991, Entomologist, 33-36). There are records from Surrey and Sussex but not biting humans.C&C did not find it out in E Anglia nor did Rory Post in his studies.

The most effective repellent is probably anything containing DEET and DMP - tedious to use. In Canada where Simulium are a real problem (like midges in Scotland) people resort to wearing hats with veils! There is very little evidence to suggest that eating marmite, etc has any real effect on repelling biting flies. Lots of ideas have been put forward with little effect.

As to why this species is more of a pest with the wheals it generates in some people will be down to a) the components in the saliva and b) the differential reaction of people (delayed hypersensitivity).

hope this helps