June 10 -Syphacia obvelata

This pinworm is commonly found in laboratory rodents such as mice and hamsters, as well as wild rodents. Because they are easy to maintain in these lab animals, they are often used as model organisms to study the biology of pinworms and to test anti-nematode compounds. This species, like some other pinworms, are capable of "retroinfection" - if the host's feces aren't moving quickly enough out, the eggs can hatch, mature, and just migrate back up the intestine to join their parents in churning out more eggs. Typically, though, the eggs are accidentally consumed by a rodent when it is grooming and go through the life cycle the normal way.. Ah, phew- that's comforting.

Image comes from this page.