Spiders are pretty common. And could certainly have been something gained via fighting in Amazonia, because there are some very wacko things down there, including - and I'm going off memory, here, so forgive me if I'm wrong - a spider that lays its eggs in the Brazilian kiwi (the one from Dunk's Will) which, if eaten, induce some pretty serious hallucinations. It was featured in either the Missions adventure book (not so sure) or else Predator and Prey (more likely).