Return of the repellent midges

When the sun comes back, we have lift-off

When the sun comes back, we have lift-off. Suddenly, an almost empty air fills up with glittering wings, as flights long delayed or held to low altitudes by wind and rain are released to boisterous heights by that great air traffic controller in the sky. Bumble-bees resume optimum schedules, butterflies their headlong indecision, hoverflies their rapt and brilliant mapping of important points in space.

And the sweat fly, Hydrotaea irritans, gathers in a cloud around my head as I kneel, stoical among the onions, tugging up clumps of horsetail, that primitive and useless fly-whisk of a weed. (No, nothing's useless: the ample silica in horsetail stems would help shore up my varicose veins, if I had any).

Even the sweat fly, nuzzling my neck and ears for water and salts, is one of the Earth's necessary "decomposers", its grubs recycling all manner of garden grot. But, as a smaller and far ticklier relation of the housefly, it also makes itself a particular nuisance to deer, swarming round their heads as their antlers are growing through the velvet, and making them stop grazing to shake their heads. This may be why red deer take to the breezier heights in summer - and why deer farmers start thinking of fly repellents.

The real menaces among flies seldom look the part, while the ones we shy away from are invariably harmless. Back in April, there was a notable hatch, widely remarked, of the St Mark's fly, Bibio marci (named for its sudden spring appearance on or about St Mark's Day, April 25th). It is very black, very hairy and flies with dangling legs - an appearance that caused some panic to early weekenders at Lough Neagh. But the fly was merely out for its beneficial business of pollinating flowers.

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My bête noir among flies that do, in fact, puncture and poison is really more bête gris. The cleg, creabhar or horse fly, otherwise Haematopota pluvialis, is a nondescript mottled grey and utterly silent in its approach.

The bane of all Irish naturalists, it particularly harrassed Robert Lloyd Praeger on his botanising summer hikes.

"Why," he wondered bitterly in The Way That I Went, "do they so frequently hunt in droves of half-a-dozen to a dozen?" The cleg is abroad from now until September, and while I put up with the inevitable, itchy bites of midges and mosquitoes in spring and early summer, those of Haematopota can raise swellings like major bruises. Thus, any news of new, non-toxic repellents that really work is of more than passing interest.

In Scotland, Dr Alison Blackwell in the Centre for Tropical Veterinary Medicine at the University of Edinburgh has become a leading authority on the ecology and behaviour of Culicoides species - the biting midges that Scotland shares with Ireland (and most of the world).

The Highland biting midge, Culicoides impunctatus, is the chief attacker, and compels outdoor workers like foresters and vets to use powerful chemical repellents applied liberally over long periods.

The key chemical, contained in varying concentrations in most over-the-counter brands, is a plastic polymer abbreviated as DEET (N,N-diethyl-m-toluamide). This, with long exposure, has been implicated in adverse reactions in the nervous system, immune system and skin, and has been cited as partly responsible for psychological effects associated with "Gulf War syndrome". As Dr Blackwell described in a recent paper for the Veterinary Bulletin, the search for safer alternatives has worked through all kinds of herbal repellents against midges, mosquitoes and clegs, including the essential oils from plants such as lemon-grass, eucalyptus, cypress, lavender, rosemary and thyme. (I regularly use citronella oil, mixed into an aqueous cream base).

But now attention has focused on oil distilled from the leaves of bog myrtle, Myrica gale, whose attractive, spicy scent is even now wafting across cut-away bog throughout our western counties. This low, wiry shrub, with fruits like tiny pine cones, is raideog or railleog, and its fragrant branches have had long, traditional use as a moth-repellent in Irish linen-cupboards.

According to Alison Blackwell, field trials proved the Myrica oil to have "repellent activity equal to that of DEET" - a claim, indeed - and a commercial repellent using it (Callanish Myrica) has secured a patent application.

It certainly sounds rather more pleasant than another new plant-based repellent just patented in North Carolina, which uses the juice from tomato stems. Much as I love tomatoes, the juice that stains my hands green when I pinch out unwanted shoots on the plants in the greenhouse has a pungent smell I can't wait to wash off.

However, according to New Scientist, it works much better than citronella, even against ticks which carry Lyme disease, now spreading in Europe. This information coincides with a paper in the current Irish Naturalist's Journal that maps the known distribution of Ireland's six tick species and the animal hosts that carry them.

In America, it is the deer tick that carries the Lyme disease spirochaete, Borrelia burgdorferi. In Ireland, ticks have transmitted both this microbe and louping-ill virus to both animals and humans. The best-known Irish tick, Ixodes ricinus infests all land mammals (including cattle and sheep) except the otter. Another, Ixodes hexagonus, which causes painful bites to humans and is a vector of Lyme disease in Germany, is confined mainly to hedgehogs, of which we would have more if badgers didn't kill them, often picking up the tick in the process.

Poor badgers - not alone do they need vaccinating against TB, they must now be sprayed with green tomato juice. . .