Pregnant Females Terrorise Coll.

What was it that ruined Queen Victoria's picnic in Sutherland in 1972? Well, of course, you all knew: it was the Highland midge: the same little creature responsible for a 20% loss of working days in forestry gangs and for a lot of headaches for the Scottish Tourist Board. In fact, the S.T.B. have come clean this year so that in their Practical Information for the traveller to Scotland under heading ‘Helpful Hints, between ‘Marriage’ and ‘Money’, we find ‘the Midge’. Here we are told amongst other things, that: ‘On warm, humid evenings, you may want to keep arms and legs covered.’(!)

Now, those of us who survived the vicious midge attacks of the earlier part of 1991 may regard the above advice as a bit weak but then many of the islanders commented on the unusual severity of midge hostilities at that time so it may just have been a bad year. Interestingly a very readable little book entitled ‘Midges in Scotland by George Hendry was published recently (1989) and the source of much of the following information.

Scotland boasts 34 species of biting midge but only 4 or 5 species regularly attack humans – the others prefer sheep, horses, cattle etc. Around 90% of attacks on humans are accounted for by a single specie – Culicoides Genghis Khanis. They’re just wee chaps – about 1.4mm wingspan – and in fact, the ones that bite aren’t chaps at all – they’re female. The males tend to hover in quite small swarms, into which the females fly and are mated. The pregnant female then needs human blood without which egg development is arrested and the minute amount required can be obtained for a single bite. The midge uses its mandibles to cut an opening in the skin, a tube is inserted and saliva is pumped into the wound to prevent blood clotting: blood can then be drawn out. Certain proteins in the saliva cause a mild allergic reaction and the release of histamine. This normal bodily defence allows the midge about 3 minutes feeding time. No 'poison' is involved: it just feels like it!

Naturally, a single midge bite is of little consequence to most people but a large number of hungry midges can deliver 2000-3000 bites per hour – although most victims will have withdrawn from the war zone long before then. Naive immune systems (i.e. tourists that haven't been to Scotland before) show little reaction at first, until the body becomes sensitised – after, say five days, when the response will be greater. Those who have experienced prolonged exposure to bites over a period of years may have ‘sluggish’ immune systems and show little response to attacks. A very small proportion of people show an abnormally vigorous response and can develop marked swelling from a single bite: they will typically show this same reaction to other biting insects as well. For most people however, a single midge bite is far less irritant than, say, a nettle sting and itching will decline rapidly after only about 10 minutes.

Proprietary brands of repellant all work to varying degrees depending on the concentration of the active ingredients – so read the cannister.

Midges commonly appear at the end of May and beginning of June although these are mostly non-biting males. Biting proper starts around mid-June and continues for about 12 weeks. Later midge bites are probably from another specie and less severe. The large, hovering swarms that can frequently be seen are also another specie (the dancing midge): these are the big 4mm jobs but they're all machismo and gold medallions and neither bite nor sting.

There are two important things to know about when avoiding midges. Firstly, the larvae need moist conditions and in consequence, midge populations are most marked in areas where rainfalls exceed 50” per annum. From the accompanying map we see that this means the West Coast generally - but notice the difference between Eastern and Western Coll! Because of this need for moisture, a particularly dry month will usually be followed about a month later by relatively low midge numbers: a dry Spring by a midge-free Summer. Prime sites can contain as many as 24 million larvae per hectare and such sites are often indicated by the presence of the Jointed Rush and Sphagnum and Polytrichum mosses. For instance, Staffa and Iona offer poor breeding sights as would predominantly rocky or sandy areas although midgey drifting can occur into such areas.

The second important factor is that midges don't like strong light and biting activity is triggered by fading light. For this reason, attacks occur early morning, evening, under cloud cover at any time of the day and in shaded areas like forests. Humidity is" unimportant: it just happens to be associated with cloud cover. Rain doesn't deter them, neither does temperature but they don’t like winds above about 5 m.p.h. and they avoid smoke and fumes. They can be found out at sea and above 1500 feet but the incidence declines. Perhaps because shade is preferred, midges seem to be attracted to dark materials, so dark clothes are not a good idea particularly if the wearer is sweating profusely. It seems likely that they home in on sweat and other secretions from a distance and then use their nasty little multifaceted eyes for close work.

It doesn't really help much to squash them but it makes you feel a whole lot better!

Now there are a few questions that can perhaps be settled in time for next year's magazine. Firstly, is there really a significant difference in rainfall between the East and West ends of Coll? If so, is there a parallel difference in the distribution of the Jointed Rush and Spaghnum moss? Thirdly, how do midge concentrations vary on Coll and between Coll and neighbouring islands? Contact has been made with George Hendry who may be able to advise as to how this last question particularly might be explored without too great a loss of life.

So that’s about it, except to add that the spitefully biting Scottish Clegg just loves warm, bright days.

Source: Midges in Scotland.
George Hendry;
Aberdeen Univ. Press,