Ants and other insects that crawl into an ear can be washed out by tilting your head, pouring water in and tilting head in other direction... you'll know there's an ant in there by the funny scratching sound in your head!
Doesn't occur that often in my experience and I only sleep in a tent when it's raining...

A Bear Vault keeps all critters out. I have a small one which doubles great as a stool in camp... especially good when the ground is wet... Great for washing clothes in as well