Williamson's Weekly Nature Notes June 17 2009

The photograph here by Brian Henham of Chichester taken on the Downs makes the tiny little female look like a giant. But she is our smallest butterfly in Britain. She is wee. So you may miss this little jewel as you walk across the Sussex chalk hills in summer.

No wonder small blues are called Cupido minimus. Small though they are, they are quite large compared to Europe's smallest butterflies like the Little tiger blue, or the Odd-spot blue.

Even smaller still is the Grass jewel of southern Greece, which has a wing span of less than 14 millimetres. Our Small blue has a wing span of 20mms.

Be wary of rather under-sized Common blue females which I have noticed sometimes never get anywhere near the 25mms of their bigger sisters.

Small blues easily give themselves away by the colours on top of their wings. The photograph here shows the lovely sky-blue of the underside. As soon as its wings open you are looking at a blob of soot. The top side of the wings is brown.

Where to look for our Small blues? Till the end of June and once again in August with the second brood, look on warm steep banks of old downland turf. Cuttings of new roadworks are sometimes favourite, like that on the A27 near Shoreham.

There is another such in Cornwall. So the steep banks of old hillforts across the chalk downs could be the place were this tiny tot might make your day.

But colonies come and go. One year there are thousands at a particular location, the next year hardly a one.

The foodplant for its caterpillars must be present: the caterpillars needing the leaves and especially flowers of kidney vetch. This plant is fairly common. In the photo, our female of the week is refreshing herself with nectar from a bird'sfoot trefoil flower.

Britain once led the world in science. So it is no surprise to find that the Small blue was first identified and named with the taxonomic handle of Cupido minimus in 1795.

The popular name given was the Bedford blue, and by others, the Little blue. Interesting to see that the latter name has now been adopted as the correct name.

You might see it here and there in the UK as far north as Caithness. A good spot is just south of Aberdeen. It even lives across Russia and in to Siberia, if you are ever lucky enough to go there.