www.ukbutterflies.co.uk

I was sneaking up on a brimstone this morning and a fly joined in. Neither seemed bothered by the other and they remained like this for several minutes. Ive not seen this before, Is it common?


Dave

I guess you get used to it when you look like a leaf!

Simon

It is common to see hoverflies and other Diptera settling on the wings of Brimstones, particularly on mornings in April and May. The flies are probably attracted to the wings because they reflect solar energy very strongly - the heat is reflected back onto the body of the fly, and converted into energy. Brimstones also reflect ultra-violet very strongly, and this is probably detected very easily by passing flies.

Lots more about butterfly behaviour at :

I photographed this dusky large blue carrying a passenger last July:

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It was similarly unconcerned.

Guy