Question
What are the bugs that eat leaves?

Answer
Johnston,

Many different insects feed on leaves. Some insects like aphids tap into the leaf's vascular system and feed on plant sap (see http://www.livingwithbugs.com/aphids.html for a picture of aphids). Some insects like Japanese beetle chew leaf tissue for food (see http://www.livingwithbugs.com/japanese_beetle.html for a picture of Japanese beetles). Of the millions of species of insects I would guess that more than half directly use leaves and other plant parts for food. If you have a specific question about a particular insect post a follow up.

Jack DeAngelis
http://www.livingwithbugs.com