Mourning cloak feeding on tree sap
An engineer asked me if butterflies can use thermals and air currents to help them fly. The answer is yes. Both the Monarch Butterfly, Danaus plexippus, and the Mourning Cloak Butterfly, Nyphalis antiopa, have been observed to gain altitude on thermals. David Gibo* reported several observations of Mourning Cloak Butterflies interacting with thermals. The Mourning Cloaks were flying close to the ground in a linear fashion, when they switched course to fly in a circle. The Mourning Cloaks ceased beating their wings and continued to rise in altitude while traveling in a circle. One observation occurred over a hot parking lot. Hot parking lots are known to generate thermals. The Butterflies were observed to soar to a height of 20-25 meters without flapping their wings. At higher altitudes, Butterflies can use directional air currents to more rapidly travel substantial distance.
*David Gibo. 1981. SOME OBSERVATIONS ON SOARING FLIGHT IN THE MOURNING CLOAK BUTTERFLY IN SOUTHERN ONTARIO. NEW YORK ENTOMOLOGICAL SOCIETY LXXXIX(2): 98-101.
