OK, I asked my partner about this (senior reader/professor in microbiology and parasitology). Main work on mosquitos (malaria), although early work on tsetse (trypanosomiasis) – really nasty little beggars btw – but, although they are different species there are some similarities.
Any errors in what follows are my faulty memory, not the source of the information.
Midges are attracted by CO2, heat and odour. The person that knows most about them is Alison Blackwell (I hope I have the name right), now retired, but the expert on Scottish midges. Look up a web site called Smidge
https://www.smidgeup.com . They have a map of midge levels. Apparently they measure the levels of midges by catchers with dry ice (CO2) and then weigh them. In kilos sometimes.
Miscellanea: midges have biting mouth parts rather than the sucking ones of the mosquito (biting and sucking…let’s not go there, sounds like a Frankie goes to Hollywood lyric). Whilst mosquitoes carry many diseases to which humans are susceptible, midges are mostly a hazard to livestock (bluetongue for example), although there is something in south America that affect humans and a midge is one of the transmission vectors.
Anyway, these Smidge people market a product as a repellent. I cannot vouch for it myself, as I have never particularly been troubled by the blighters, despite having travelled around the west of Scotland quite a lot. But that is perhaps, as my partner delicately pointed out, because I was either sailing, or in a pub, restaurant or night club. I wonder if the Ritz in Rothesay is still going. Possibly the worst nightclub in Scotland, Or would that be Room at the Top in Livingston, or Fat Sams in Dundee. Actually the list is endless, and I digress…