Evidence of carnivory for harvestmen in Belize based on stable nitrogen isotopes and fecal samples
Abstract
Harvestmen are generally considered to be omnivores. In contrast to most other arachnids that are fluid feeders, harvestmen are capable of ingesting solid food particles and may consume invertebrates, small vertebrates, plant tissues, fungi, and detritus. However, for most species, quantitative diet data are lacking. Stable nitrogen isotope analysis provides a means to measure the contribution of these materials to the diet over the time scale of tissue turnover, and thus quantify trophic position. Examination of fecal material can provide additional evidence of recent feeding, which can further complement field observations and isotopic analyses. We investigated the diet of Erginulus clavotibialis (F.O. Pickard-Cambridge, 1905) (Arachnida, Opiliones, Cosmetidae) in western Belize, using stable isotope analysis and scanning electron microscopy of fecal samples. We also examined nitrogen isotopic ratios for carnivores (scorpions and spiders), herbivores (grasshoppers and katydids), and preliminary measures for two other harvestmen species, ants, and termites. Erginulus clavotibialis had δ15N signatures similar to scorpions and spiders, indicating carnivory. Nymphs and adults (females and males) of E. clavotibialis did not differ significantly in their trophic level despite possessing chelicerae and pedipalps that differ substantially in relative size and morphology. Fecal samples contained considerable evidence of arthropod consumption, as fragments of legs and exoskeleton were evident. Our study provides an initial quantification of harvestman diet and documents that E. clavotibialis is primarily carnivorous.
M. H. Schaus, V. R. Townsend Jr., S. A. Wiltshire, M. C. Metro "Evidence of carnivory for harvestmen in Belize based on stable nitrogen isotopes and fecal samples," The Journal of Arachnology, 53(1), 54-61, (17 July 2025) https://doi.org/10.1636/JoA-S-23-031
