I've tried to find the specific page where it states it but it is a fact that it is against the law to send snakes through the postal service. The accept lizards but not snakes, I think turtles are a no no as well. And I just saw that poisonous spiders are also non mailable. That pretty mauch makes everyone sellin T's on line a law breaker as every single tarantula order I have ever gotten has come USPS. Check out his link if it works.
http://www.usps.com/cpim/ftp/pubs/pub52.pdf