Fruit flies have individual unlearned preferences in smells they prefer and choose to fly primarily in the air with that smell.
Fruit flies learn whether smells lead to reward, punishment, or neither.
Fruit flies retain memories for at least three hours.
These are rather small but I never think of fruit flies as thinking, learning, deciding, or remembering. It makes it pretty impossible for people to argue that cows and chickens don't think when even fruit flies do.
Writing memories with light-addressable reinforcement circuitry
Adam Claridge-Chang, Robert D. Roorda, Eleftheria Vrontou
I also read in an article that they respond to peer pressure when choosing a mate, although I can't find it at the moment. I don't think the size of an animal is relevant to their intelligence; bees and ants are intelligent but compare their size to pigs, humans, dolphins and elephants!
"Treat others as you wish to be treated."
- The Golden Rule
"No snowflake in an avalanche feels responsible."
"Be the change you wish to see in the world."
- Mahatma Ghandi
"Even dust piled up will grow into a mountain."
- Japanese Proverb