Suppose we discovered an ET that looked like a tarantula.... I would find it extremely disturbing to be faced with the prospect of trying to communicate with a tarantula if it were intelligent, but if it were merely an animal there wouldn't be any pressure. No more than any other species on earth. We could poke at it, take pictures, and it wouldn't know the difference. But if it were intelligent, I'd probably be a bit more careful. And, with the variety of life found on earth, given the Carboniferous Era oxygen levels, it may be quite possible to find a planet somewhere inhabited by a race of gigantic, and intelligent, predatory bugs. There are fossils on earth of 8-foot long centipedes. That's as big as a crocodile, with lots of legs used for grasping its prey (or maybe tools perhaps). On Earth, these things fed upon mammals. They still do in fact. If the small ones eat rats, the big ones probably ate wild boar, small horses, monkeys, pretty long list of possible foods...

Giant Centipede eats rats