It's a fair point, but I guess we would recognise them, especially if carbon-based.

Think of another issue. We evolved in 6 million years. Assuming it takes 4 billion for the planet to form and organisms to form, that means there's 8 bln years where civ can start. What's the chance that they are at a similar tech level as us? Really small.

Do you stop to talk to an ant on a field trip?