Oookay, am I the only person who would spy? SERIOUSLY. If you guys got this ability it would be a massive waste. I would spy, sneak, steal, play pranks, do all sorts of things. Well maybe not steal big things, but sweets and stuff -- not from my friends, but from other people. I have the courage to be honest! Don't judge me!
Yes, I would be terrified of bugs. Yes, I would be terrified of birds. If I saw them coming I would crap myself, but you said the power can be controlled, so I would simply wait for said bird/bug to get close enough then BAM! Massive again. [Insert some drawn out insect/animal cruelty.]
Finally I agree with the flying thing. I would spend hours flying, but it'd have to be somewhere safe so that a bird doesn't get me from behind.
...Urgh, imagine coming across a big spider when you're that size? That would be horrifying. You'd see their eyes and the hair and their whole bodies in detail.
*Throws up*