miked's picture

Miked's 220th spot submitted on 3rd August 2009

Observed: 2nd August 2009 By: miked
iSpot team
miked’s reputation in Invertebratesmiked’s reputation in Invertebratesmiked’s reputation in Invertebratesmiked’s reputation in Invertebrates
MG 1757

common blue or small blue. there were a few blue butterflies such as this one that were much smaller than the rest of the common blues on this chalky site

Species interactions

No interactions present.

Species with which Common Blue (Polyommatus icarus) interacts


Martin Harvey's picture


Mike, try scrolling down this page on UKbutterflies and comparing Small Blue with Common Blue:

Entomologist and biological recorder

miked's picture

Yes I had done that (checking

Yes I had done that (checking the uk butterflies website) before posting the observation and it seemed to be common blue what i really wanted to know was is it possible to have such a wide variation in size in the field and still be the same species? There were plenty of common blues both male and female and they were all of a similar size but then a few of this kind of butterfly that were significantly smaller, perhaps half or 2/3 the size of the rest of them.
Are there perhaps local races of common blue that are smaller?

Martin Harvey's picture


Okay Mike, I just thought you might want to put an identification against this one before we went further. It's certainly possible for insects to be smaller than usual in some circumstances, e.g. if there was a lack of food for the larvae, or if they are stressed in some other way during development. Some species are more prone to this type of variation than others. As far as I know Common Blue is not considered to be particularly variable in size - the books quote a wingspan range of 29-36mm, and while there are bound to be the occasional outliers that are beyond that range it would be considered unusual I think.

Common Blues out now are likely to be from their second generation this year, and the second generation is often a bit smaller than the first, but that doesn't explain why you're seeing a mix of sizes.

I don't see how your photo can be anything other than a Common Blue, the colour is wrong for Small Blue. But I don't have a satisfactory explanation for why there were two different sizes in the College Lake population.

Entomologist and biological recorder