Adult
Emerald ash borer adults are small, metallic green beetles that are 1/2 inch long and 1/8 inch wide (smaller than a penny). Adult emerald ash borers emerge from beneath the bark of ash trees in May through mid-July, creating a D-shaped exit hole. Adult beetles are most active during warm sunny weather. They have a limited distance they can fly (1 mile to 4 miles) depending on the wind. Once they find a mate, the female can lay 60 - 90 eggs in the crevices of ash tree bark. Adult beetles will feed on ash tree leaves creating "notches" that does not harm the tree. It is estimated that adult beetles live up to six weeks after emergence.
An adult Emerald Ash Borer is ½ inch long and 1/8 inch wide, or just a little smaller than a penny.
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An adult Emerald Ash Borer feeding on ash leaves during the summer. The feeding creates "notches" of missing leaf material that causes minimal to no damage to the trees health.
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Eggs 
Emerald ash borer eggs are small (1 mm) and very difficult to find. Female adult beetles deposit them in the bark crevices, and larvae hatch from the egg. The larvae immediately chew their way through the bark into the vascular system of the tree.
Larvae (immature stage of EAB)
Emerald ash borer larvae are white and slightly flattened, with a pair of brown pincher-like appendages called urogomphi on the last abdominal segment. Their size varies as they feed under the bark on the ash tree's tissues and grow. Full grown larvae average 1.5 inches in length. EAB larvae feed in a S-shaped pattern, which is a diagnostic characteristic to this pest.
Different developmental sizes of Emerald Ash Borer Larvae. Notice that the last few segment have a "bell shape", which is another diagnostic characteristic.
The feeding galleries just under the bark.
Notice the "S" shaped pattern, which is another diagnostic tool.
Pupa
During the fall, the larvae will create a chamber inside the sapwood of the tree to mature in. They stay in this chamber until spring when the adults emerge from a pupa case and leave the tree completing the life cycle.
The emergence hole that is left after the Emerald Ash Borer adult leaves the tree.
Notice that the hole is in the shape of the letter "D", which is another diagnostic tool.