Why?

MariaBBB

May 10, 2010 1:43pm

There are several reasons for this. Many Nymphalids including Hamadryas, Prepona, Panacea and the Red Admiral Vanessa atalanta habitually bask high up on tree trunks, with wings outspread, and head downwards. They often appear to be observing the activity below them, and males certainly use these high vantage points to watch out for females flying below them in the forest. An additional advantage of adopting this position is that sunlight hits the wings more squarely, allowing the butterflies to warm themselves more quickly.

Another reason is linked to aerodynamics. Studies have demonstrated that butterflies get greater "lift" if they take off from a head-downwards position. The butterflies probably make use of the heat reflected up from the leaf litter, and in conjunction with the more efficient head-downwards take-off, can become airborne more easily on the cold but sunny days of late winter and early spring.