The world's leading expert on midges has been left scratching her head after the ravenous beasties suffered a huge drop in numbers.

Alison Blackwell, of Dundee-based Advanced Pest Solutions, said the number of the biting insects caught in traps across Scotland were well down on July catches in previous years.

But she was unable to explain the decrease.

Alison, whose company runs the Scottish Midge Forecast, said: "We had some big catches in June, in some places around double what we had for June last year, but they have reduced significantly this month.

"I don't really know why the numbers have tailed off, but I suspect there has been a warm dry spell when we would normally expect the second generation to emerge, which has delayed the second hatch.

"Where we've had quite a hot spell, followed by not enough rain. I suspect there have been a few deaths. But I'm still expecting them to appear - just later than usual."

The larvae of Culicoides impunctatus - the scientific name for the Highland biting midge - overwinter in the soil and begin to emerge as adults in May and June the following year.

These adults then lay eggs that develop relatively quickly to give a second emergence of adult midges in July.

And a third hatch can occur in September if the second half of the summer is particularly warm.

Alison said a carbon dioxide trap in Inveraray, Argyll, had caught around 500,003 midges each night in June, but only 20,000 per night this month.

Only 8,500 were recorded on July 19.

A similar trap in Gairloch, Wester Ross, had picked up around 34,000 per night in June and an average of 4,200 this month.

But Alison said numbers were beginning to pick up, with 76,700 captured in Inveraray on Sunday night.

The midge forecast, which provides advice for hikers and others taking part in outdoor pursuits based on the weather forecast and catches from traps across Scotland, will run until the end of the midge season.