Wednesday, 12 September 2012

In search of thunder

The chances are that you will be familiar with ‘thunderflies’, those tiny dark insects that are most evident during the muggy warmth of hot, late summer days. Look around the framed pictures in your house and you might even spot the body of one that has insinuated itself behind the glass of a treasured picture. You might have swallowed more than one if a keen cyclist or jogger, or had one get caught in your eye while out on a walk. For their size, these diminutive insects can be disproportionately annoying! But how much do you really know about them? Did you know, for example, that they belong to an order of insects known as Thysanoptera (which means ‘fringed wings’) or that they are commonly called thrips? If you did, then were you aware that the singular of ‘thrips’ is ‘thrips’ and that there is no such thing as a ‘thrip’?

Size matters when it comes to our interest in insects; size and economic value. We humans rarely take much of an interest in something as small and seemingly insignificant as thrips, unless it happens to impact on our way of life. Thrips, and there are somewhere in the order of 150 species known from Britain, include species that are pests of agricultural products, from glasshouse crops to cereals, peas and even onions. Some feed on plant leaves, their populations sometimes reaching levels where severe damage is caused to the plant, which may become stunted and turn yellow. The damage occurs because the thrips suck out the liquid contents of the leaf cells, occasionally inadvertently introducing a damaging virus to the plant in the process. Others feed on flowers, extracting the contents of pollen grains, or feed on fungi, often out of view beneath rotting bark.

Those most commonly encountered in the field tend to be the ones that feed on flowers. The dark adults often stand out against the brightly-coloured background of the flower. Earlier in the year you may have noticed black thrips on ox-eye daisy. These are likely to have been feeding, mating or egg-laying, the eggs deposited into the florets. At this time of the year, look on heather or bell heather for other species.

While you should be able to be able to recognise a thrips for what it is, taking the identification further (to family or species level) is particularly challenging. A high-powered microscope is essential, together with an identification key and hours of patience. It is perhaps better then to appreciate them in a generic sort of way, as tiny insects whose countless numbers are testament to a successful way of life. You might even come to admire the success of such a tiny creature.

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