I'm still looking into the "ISTA Certified Packaging" requirement, but in the meantime, I found this on a U.S. Postal Service website:
9.3.3 Small Cold-Blooded Animals
"Small, harmless, cold-blooded animals (except snakes and turtles) that do not require food or water or attention during handling in the mail and that do not create sanitary problems or obnoxious odors are mailable (e.g., baby alligators and caimans not more than 20 inches long, bloodworms, earthworms, mealworms, salamanders, leeches, lizards, snails, and tadpoles)."
found at:
http://pe.usps.com/text/dmm300/601.htm#wp1064884
However, I have had NUMEROUS experiences with USPS "Overnight" service actually taking more than one day... So I would personally not recommend shipping a live animal with them...
-- Celeste