On Thursday and Friday, I worked with the US Fish and Wildlife Service to monitor populations of the threatened Ozark cavefish and the Benton cave crayfish in northwest Arkansas. We visited two caves, spending 7 hours in the first cave on Thursday and 3.5 hours in the second cave on Friday. (I'm deliberately not mentioning the names of these caves since they'd be easy to find if I did. Access to both of these caves is restricted to protect the animals living in them). The Ozark cavefish is found in less than 10 caves in Northwest Arkansas, but it is also known from sites in Oklahoma and Missouri. The Benton cave crayfish in found in only 4 caves in northwest Arkansas, and it is one of the rarest crayfishes in the world. In both caves, populations of these to species appear to be stable, with a total of 194 cavefish and 43 cave crayfish counted. Because unrestricted human visitation to these sites can greatly effect the populations by stressing animals and/or killing individuals by trampling, we only monitor every other year.