De Zwervende heidelibel (Sympetrum fonscolombii (Sélys)) in Nederland in 1996

In the first half of June 1996 a remarkable invasion of S. fonscolombii was observed in The Netherlands and adjacent countries. Three months later tenerals and exuviae were found at many locations. A total of 167 records of atleast 570 adults at 82 localities scattered all over the country are presented. Earlier records are known from only ten sites but do include reproduction. Habitat preferences and observed sexratios are discussed. The unusually easterly tendency of British records and the numerous occurence in Western Europe suggests a more eastern origin of the invasion in 1996 than seen in earlier years. Colonisation is suggested as the most likely explanation for the invasion, analogous to frequent colonists among the butterflies. The invasion occured simultaneously with that of two of these, the Painted Lady (Cynthia cardui) and Silver Y (Autographa gamma). It is unknown whether remigration of invasion offspring has occured.