butterfly drink England english ephemeral feed fly Great Britain insect invigorate Lepidoptera life natural nature nourishment perch Pieridae Pieris rapae refresh rhopalocera roost small suck summer Surrey sustenance transient white animal antenna Arthropoda british compound eye dainty delicate eye fragile hindwing Insecta leg Leptidea sinapis rare rest scale scales scarce sit tiny underside vein venation wing wood white