Harvestmen (Opiliones) represent a diverse group of arachnids, with more than 6,500 species described worldwide; see here for a complete list. Everyone seems to be familiar with these animals which have an oval/round body and long-long thin legs; this why their English common name: ‘daddy-long-legs’. However, there are short-legged species as well. The harvestman fauna of the La Selva Natural Reserve (Costa Rica) consists of about 40 recorded species, half of which remain unnamed yet (Proud et al., 2012).
One of the interesting and commonest species of La Selva is Prionoistemma sp. (family Sclerosomatidae). This species has a small round pink body with black lateral spots and very long legs. Harvestmen usually spend the daytime on the trunk of large trees, at their bases, while during the night time they actively walk up and down the trunk and also over the undergrowth vegetation. When someone approaches them, the creatures begin to shake all over on their thin legs becoming almost invisible for a spectator.
The majority of harvestmen are omnivorous feeding on a variety diets, and seem to be effective predators. On the short video given below it is seen that this Prionoistemma male is feeding on a jumping spider (family Salticidae). The jumping spiders are very active and effective diurnal predators, with sharp colourful vision. Very few predators are capable of capturing them. How on the earth could this harvestman have seized the jumping spider remains a mystery. I’ve never observed this myself earlier.
Proud D. et al., 2012. Diversity and habitat use of Neotropical harvestmen (Arachnida: Opiliones) in a Costa Rica rainforest. – ISRN Zoology, doi: 10.5402/2012/549765