Black hairstreak forewings. The most conclusive way to distinguish the two is by the row of black spots accompanying the orange band which the white-letter hairstreak never has. They spend most of their lives in the canopy or in dense scrub, feeding on honeydew, and very rarely come down to ground level. Eggs are laid singly on young blackthorn "Prunus spinosa" growth and it is this stage which hibernates. Although blackthorn is the main foodplant, wild plum "Prunus domestica" and other "Prunus" spp are occasionally used. The caterpillar hatches the following spring, at the end of April, just before the buds open
Prunus subg. Padus "Padus" is polyphyletic and is therefore invalid as a genus, subgenus or anything else. In Finland and Sweden, the blooming of bird cherry ("Prunus padus", Finnish "tuomi") signifies the start of the summer for many people. In southern Finland, this normally takes place during the two last weeks of May or very early June. North Dakota State University agriculture information page about "Prunus virginiana" Prunus subg. Padus Prunus" subg. "Padus (bird cherries) is a subgenus of "Prunus", characterised by having deciduous leaves, flowers 12-30 together on slender racemes produced in late spring well after leaf emergence, and small, sour fruit