Monarch

The Monarch butterfly, Danaus plexippus (L.) can be found at Fermilab beginning in June and sometimes in great numbers in late summer, early fall. It is one of the few butterflies that migrates. The butterflies that travel south in the fall overwinter in the south. They may reproduce in the southern wintering grounds or enroute to the North in the spring. The butterflies you see in the summer at Fermilab are not the same individuals that left there the preceeding fall, but their offspring. Two or more summer generations may be produced in the North and then the fall generation returns to the same wintering grounds even though it is three or more generations removed from that of the previous winter. The principle wintering grounds are in Mexico, but some monarchs overwinter in Florida, Cuba or southern California.