Hedgehogs usually/typically eat vegetables seems like a reasonable translation to me

I said "A hegdehog usually eats vegetables" but it wasn't accepted. A/the is not even distinguished as different in Korean

usually is not '보통', normally, typically, generally is 보통. usually is 자주 or 주로

Hedgehogs usually eat bugs, worms etc.

I think it should be either "(A hedgehog/ hedgehogs) usually eat vegetables."