What does EAB Look Like?
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Emerald ash borer has four distinct life stages:

Adult

Emerald ash borer adults are very small, metallic green beetles. Only 3/8 - 1/2 inch long and 1/16 inch wide (about the size of a cooked grain of rice), they can easily fit on a penny with room to spare! Adult emerald ash borers emerge from beneath the bark of ash trees late May through mid-July, creating a D-shaped exit hole as they chew their way out of the tree. Adult beetles are most active during the day and prefer warm, sunny weather. They never wander far from where they exit a tree (less than one mile) in search of a mate. Once they find a mate, the female will lay 60 - 90 eggs, one at a time, in the crevices of ash tree bark. The adult beetles will feed lightly on ash tree leaves, but do not cause much harm by doing so. The adult beetles live a total of three to six weeks.

Eggs

Emerald ash borer eggs are very small (1 mm), difficult to find and are rarely seen. Female adult beetles deposit them in the bark crevices and as larvae hatch from the egg, they immediately chew their way into the tree.

Larvae (immature stage of EAB)

Emerald ash borer larvae are white and slightly flattened, with a pair of brown pincher-like appendages (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. They wind back and forth as they feed, creating characteristic S-shaped patterns called galleries under the bark (starting in the phloem and extending into the xylem layers). An example of this is shown in the picture above. Larvae will feed under the bark for one or two years (longest in healthier trees), and can survive in green wood, such as firewood, even if the tree is no longer standing.

Pupa

In autumn, after one or two years of feeding under the bark, larvae will create a chamber for themselves in the tree's sapwood. They stay in this chamber over winter and pupate in the spring, turning into adult beetles. The adults emerge from the pupa case and then emerge from the tree, completing the life cycle. The pupae, like the larvae, cannot be seen unless bark is pulled away from the tree.

EAB Look-alikes

There are numerous metallic green insects common to Wisconsin that could easily be confused with emerald ash borer. For more information on these look-alikes please view the "related documents" below and visit the University of Wisconsin - Madison's emerald ash borer webpage. (Please note that the six-spotted tiger beetle may appear to have any number of spots, including zero).



Related Documents
MI Extension Bulletin about emerald ash borer look-alikes and native borers. Images included.
EABlookalikesE2939MIBulletin.pdf

More emerald ash borer look-alikes. Don't confuse these insects with EAB. MI Extension bulletin.
EABlookalikes2E2944MIBulletin.pdf

Still more EAB look-alikes. Wisconsin DNR.
EABlook-alike.pdf

A drawing of the EAB life cycle, with pictures and descriptions. A. Wagner, USDA APHIS PPQ
EABLifeCycle.pdf


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Related Images

When EAB adults exit the ash tree they leave behind tiny D-shaped holes (about 1/8 inch).


Fourth instar (full-grown) emerald ash borer larva. 1.5 - 2 inches long. WDNR Photo by Shane Lishawa


An adult emerald ash borer is a small metallic green insect, only 1/2 inch long and very narrow. These adult beetles are rarely seen because of their small size and because they are only present for 3 - 6 weeks each year.



An adult emerald ash borer on a U.S. penny

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