The Monarch butterfly Danaus plexippus (Linnaeus, 1758) in the Strait of Gibraltar (Lepidoptera: Danaidae)

The distribution of the Monarch butterfly Danaus plexippus (L.) has been studied in an area close to the Strait of Gibraltar (southern Spain). The butterfly presents a fragmented distribution related to that of the Asclepidaceae Gomphocarpus fruticosus and Asclepias curassavica, which are the food-plants of their larvae and the main nectar source of the butterflies. Sixty-three patches with different combinations and abundance of one or both species have been located. During 2008 the Monarch butterfly was located in 36 of those patches, in variable numbers, up to 100 individuals flying simultaneously. Within these high-density patches, larvae not only completely defoliated the annual investment of plants, but also consumed flowers, fruits and apical steins. As a consequence, butterflies dispersed to other more favourable fragments. The appearance of this species in different localities of the Iberian Peninsula should be related to a metapopulation dynamic with dispersing individuals moving between patches. Sporadic arrival of individuals coming from other continents can not be excluded.