THE MATING-BEHAVIOR OF THE EARTHWORM LUMBRICUS-TERRESTRIS (OLIGOCHAETA, LUMBRICIDAE)

A field observation suggested that the mating of the earthworm Lumbric us terrestris L. might involve a pre-copulation behaviour sequence dur ing which prospective partners visit each other's burrows. This was st udied in laboratory investigations, where pairs of Finnish, field coll ected L. terrestris were observed directly and behaviour of groups of four or nine previously unmated L. terrestris of English origin was st udied by video-recording. In total, 15 full mating sequences were reco rded. Mate searching involved trail-following on the soil surface. Thi s was followed by a series of, usually reciprocated, burrow visits. Th e number of visits by an individual worm showed a high degree of varia bility (n = 1-17). A burrow visit typically consisted of anterior segm ents insertion, for a period of 30 to 50 seconds, but also deeper burr ow-penetrations, which sometimes lasted several minutes, were recorded . Resident worms, when visited, either withdrew below ground completel y or remained at the surface, with the first few anterior segments in view. Visiting worms normally retained their posterior segments in the ir own burrows. Visits were fewer when burrow openings were more widel y separated. Partners often maintained close contact while moving back and forth between the burrow openings and the pre-copulation phase ap peared as specific courtship behaviour. Uninterrupted, the pre-copulat ion behaviour sequences lasted from 11 to 22 minutes in video-taped ma tings and approximately 90 minutes in the single directly-observed mat ing. After a pre-copulation sequence, pairs adopted a static 's'-shape d copulation position of close ventral contact, during which both indi viduals bent their anterior segments away from the partner's body. Cop ulations lasted from 69 to 200 minutes (median length for video-taped matings 135 minutes). Other individuals often touched the copulating p air. Where this occurred, matings were shorter compared to those with no interference. We present a scheme for the mating of L. terrestris, discuss its different phases and propose a few lines for further studi es.