The only obstacle that stands between George McGavin and a verdict over whether he has discovered the smallest winged insect in the world is a pile of 11,500 dead arthropods waiting to be sorted.

The irritating thing is that he believes he has already spotted and collected the tiny insect. But a being of such size is easily lost - two such insects could perch together on one of the tiny dots that line a penny's circumference.

The insect, which Dr McGavin, an entomologist, gathered in north Tanzania, has also been seen by royalty. For, by coincidence, the Duke of Kent, honorary president of the Royal Geographical Society, was at that moment visiting the project, which is run by the RGS and the Tanzanian government's department of wildlife.

Dr McGavin works by spraying an environmentally friendly insecticide at trees and then catching the insect fall-out in sheets that have been suspended underneath.

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"To show the Duke of Kent what I was doing I sprayed an Acacia Senegal," he said. The Duke seemed interested, so Dr McGavin hunted around and found "an old optical instrument, whose eye piece had no scale", to show off some of his finds. While he was doing so, he noticed that one insect, from the Mymaridae or wasp family, really was particularly small. By comparisons with other insects, he worked out that it was 0.21mm long, and carefully stored it with the other 11,499 that came out of the same tree.

Back at the university museum at Oxford, where Dr McGavin has been working on the myriad of insects he collected in Tanzania, many of which are previously unknown species, long searches failed to yield the insect. "We have been through all the tubes and the smallest I can find is 0.25mm," he said.

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He has several theories. Perhaps his rudimentary measuring system in Tanzania led him to exaggerate the as-yet-unnamed insect's smallness.

Perhaps his preservative has swollen the insect slightly. Or perhaps, as it is so small, it is clinging to the back of some larger neighbour and has evaded discovery.

It could be that 0.2mm may be as small as insects get. Water and air may be too viscous to be managed by a tinier system. As it is, tiny insects' wings are designed to row, rather than fly through the air.

But, says Dr McGavin, "the general trend over time has been to become small, to avoid enemies". As the search goes on it looks like this one has succeeded.

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