Nyssodesmus python is a large (up to 100 mm--four inches--in length) millipede which is quite common in Costa Rican rainforests. Almost always seen in pairs, a male "rides" a female. This simple form of mate guarding prevents the female from mating with another male. Copulation occurs within a few hours of a male mounting the female, but the male and female may stay together for several days. Adolph and Geber (1995) found that 69% of these millipedes were paired at any given time, and that solitary animals were receptive for mating.

Nyssodesmus python are abundant and visually obvious. Predation seems, however, to be infrequent. A potent chemical secretion composed of cyanide and benzaldehyde protects them from would-be predators. In addition, their exoskeleton is calcified, making it much harder than that of a typical arthropod.