What is the lowest form of life that engages in play?

Dolphins, chimps, puppies, kittens, and bunnies play. I’m pretty sure bugs do not play. Do mice? Chickens? Lizards? Frogs? Fish?

For purposes of this question, let’s set aside epistemological concerns and assume that ethologists (or pet owners, farmers, hunters, or whoever happens to be observing these creatures) can correctly identify play behavior when they see it.

Anecdotes welcome. Jokes/puns about “lowest form of life” are not (so don’t answer “men”).