Aspects of the Natural History of the Arboreal Harvestman Cynorta marginalis (Opiliones: Cosmetidae) Inhabiting a Costa Rican Forest

Abstract

Relatively little is known about the natural history of the cosmetid harvestmen that inhabit the forests of Central America. The primary objective of this study was to investigate habitat use among adult Cynorta marginalis. In the field, we established 15 transects (40 m in length) and sampled them repeatedly in the morning (0830–1100 h) and evening (1800–2300 h). During 45 morning and 35 evening surveys, we captured and marked 146 males and 112 females. Only three individuals (all females) were recaptured over the course of the study, indicating that the population size at this field site was relatively large. Heavy rains significantly reduced the surface activity of adults (1.1 individuals per transect during heavy rain vs. 3.7 individuals per transect during light or no rain). Harvestmen most commonly used leaves (65% of captures) or tree trunks (31%) as perches, and rarely occupied branches or the leaf litter. Only 18 adults were observed with leg injuries, with two individuals having damage to multiple legs. Perch height was significantly lower during the evening (110.9 cm at night vs. 155.1 cm during the day). Adults were most commonly found alone (85%), however, we observed several harvestmen in male-female pairs (8%), same sex pairs (4%) and heterosexual groups (3%). Although we did not observe reproductive or aggressive behaviors in the field, we observed intraspecific interactions under laboratory conditions and found that some individuals (15%) engaged in courtship suggesting that the sharing of perches by male-female pairs may be related to reproductive activity.