The Two-tailed Spider or Tree Trunk Spider, Neotama mexicana, is a member of the Family Hersiliidae and ranges from the United States to at least Peru and across northern South America.  They have very long spinnerets on the rear of the abdomen, and are cryptic while sitting on lichens on tree trunks.  This habit is so common that for years we simply called them lichen spiders.  When disturbed, they move very quickly.