Snakes can be pretty much anywhere. There have been numerous reports on the DIS of snake sightings at WDW.
If WDW has to warn us about every possible act of nature via wildlife, then the signs would be everywhere.
Florida is home to brown recluse spiders and black widows, 6 types of venomous snake (another site said 5 in the WDW area), and wild boars! Yes, wild boars live on WDW property.
[Sure enough, there's multiple tours you can pay- right near WDW- to take you boar hunting! or gator hunting, "in the swamps of Kissimmee from an airboat", if you prefer. You can also hunt coyote. You don't have to go far from WDW.]
What about rabies? May 26, 2016- rabid deer found in Sarasota, FL. Another one was issued for Pasco in April, and Tampa in Feb (these are a bit from WDW, but still - that's 3 in FL this spring so far)
What about the armadillos? They harbor leprosy, and are fairly common in the WDW area they are also very hard to keep out, because they burrow under fences and climb over them. I think WDW must have removed many of them, because a few years ago we saw them all over WDW, but more recently we haven't seen them.