Fleas.
When fleas do very many grow,
Then ’twill surely rain or snow.
When eager bites the thirsty flea,
Clouds and rain you sure shall see.
Flies.
A fly on your nose you slap and it goes,
If it comes back again it will bring a good rain.
When flies congregate in swarms, rain follows soon.
When flies bite greedily, expect rain.