A soft layer of hair expands the surface area of a fishing spider allowing it to “walk on water” as it seeks its prey. Capturing a bubble of air, the spider submerges breathing though its book lungs, as it hunts for fish and aquatic insects. It may remain silent on a rock above the water’s edge detecting subtle ripples across the water. As its fore legs sense vibrations, it lunges towards its prey injecting it with venom. I first encountered these impressively large spiders while backpacking through the heart of the Osa Peninsula, Costa Rica. On our recent expedition to Belize, we kayaked through a series of underground caves encountering fishing spiders, roosting bats and “Pica Culas” or Ass Biters, a small voracious fish that shares the same family as the Red Bellied Piranha, Characidae.