Evidence for a directed southward autumn migration of nocturnal noctuid moths in central Europe

Insect migrations are spectacular natural events and resemble a remarkable relocation of biomass between two locations in space. Unlike the well-known migrations of daytime flying butterflies, such as the Painted lady (Vanessa cardui) or the Monarch butterfly (Danaus plexippus), much less widely known are the migrations of nocturnal moths. These migrations – typically involving billions of moths from different taxa – have recently attracted considerable scientific attention. Nocturnal moth migrations have traditionally been investigated by trapping and by observations in the wild, but in recent times a considerable improvement in our understanding of this phenomenon has come from studying insect movements using vertical looking radars. In order to establish a model organism to study compass mechanisms in migratory moths, we almost accidently encountered an extraordinarily directed flight performance in a Noctuid moth, the Red underwing (Catocala nupta) and revisited the migratory behaviour of the Large yellow underwing (Noctua pronuba). Interestingly, the orientation performance of the Large yellow underwing was impaired on humid nights. Both species performed flight behaviour under an unobscured view of the sky and a natural Earth's magnetic field. We found no evidence for a non time-compensated compass mechanism as it was suggested previously.