AS others have said, unfortunately the midge season mirrors the biking season up here May to Sept. (i'm sure there are probably some 'real midges' who claim to fly all year round and look down on the 'fair-weather' midges." />.)
The worst months are usually June, July & August. so May is probably a good time to come (quite often May can be the best month for weather too). The 'Skin So Soft' stuff from Avon is a good tip (at the Carbeth they used to always have some on hand for folk sitting outside in the evenings... quite amusing seeing all the rufty tufty bikers slathering themselves with Avon 'Skin So Soft' lotion " /> - bear in mind it's not a 'cure' ..if the midges are out in force you will still get bitten... but not quite so much) Smoking a fag also helps, but taking up smoking probably isn't the best of remedies!
To be fair the midges don't come out if there is a breeze and they don't like sunshine..... I have never been troubled by them whilst out riding ...the problem comes if you stop and sit outside at dusk in the evenings...even then it can vary from spot to spot ...depending on how close you are to water. You can be plagued at one place ...but a few miles down the road be fine.
Don't forget if you are up here anywhere near Glasgow on a Sunday (or north west of Glasgow) we are out riding most weeks, so feel free to join us for a day's fun.....or just to meet up if you prefer. We are normally out around Callander / Tyndrum / Glen Coe / Inveraray / Lochgilphead (Same goes for you and Mr H too, Mrs. H)