There are at least twelve species of carpenter bees occuring in the United States. Their nesting activity can vary; some prefer rotting decayed wood,and others the pithy or hollow stems of plants. Some species become economically important when they nest in sound structural wood. Carpenter bees which nest in wood are large 3/4 to 1 inch long. They are metallic blue-black and have green or purplish reflections and are covered with orange or bright yellow hair. Carpenter bees resemble bumblebees in size and coloration except for the top of the abdomen, which is black and usually has no hair. Bumblebees have some yellow hair on the top of the abdomen. Female carpenter bees also have a dense brush of hairs on the hind legs but bumblebees have unusually large pollen baskets.