How to tell a carpenter bee from a bumblebee

Carpenter bee appearance:

Carpenter bees have a bare, shiny abdomen that's all black. They measure about 1 inch long. The thorax on some carpenter bee species is yellow; other species have a white, black, brown or blue thorax. 

Bumblebee appearance:

A bumblebee's head, thorax and abdomen are all fuzzy. The thorax has a thin yellow band, and the abdomen is yellow and black. Bumblebees can range from 3/4 inch to 1.5 inch in length.

Carpenter bee nests:

Carpenter bees make their nests in wood, drilling a hole and then turning 90 degrees to excavate a tunnel in which to lay eggs. 

Bumblebee nests:

Bumblebees build their nests close to the ground, in places like compost heaps, wood or leaf piles, or abandoned rodent holes. 

Carpenter bee colony:

Carpenter bees are solitary bees and do not form colonies. They live in small nests constructed by one female who bores into wood to lay her eggs in several small cells. 

Bumblebee colony:

Bumblebees are social insects that live in colonies of 50-400 bees. There is one queen, and the other bumblebees gather food to serve her and care for the developing larvae.

Carpenter bee habits:

Carpenter bees hover around wood siding, decks, eaves and fences to excavate a nest or feed the larvae inside.

Bumblebee habits:

Bumblebees visit flowers to collect pollen and nectar. They can make flowers release pollen through the fast vibration of their wings. 

Carpenter bee aggression:

Male carpenter bees are known for "buzzing" the heads of humans in an aggressive manner, but they cannot sting. Female carpenter bees can sting if the nest is threatened.

Bumblebee aggression:

A female bumblebee can sting, and will do so repeatedly without losing its stinger. Bumblebees are typically not aggressive unless the nest is threatened.