Giant Resin Bee

I've seen them here (Philadelphia, PA) only in the last two years.
The males hang around the nest but are not aggresive and can't sting anyhow.

http://bugguide.net/node/view/15541 - really nice living shots on this website- worth seeing
by Beatriz Moisset

Identification
They have a cylindrical body ranging from 1/2 to almost one inch (14 - 24 mm) in length, which is longer than most other bees in North America. The females tend to be larger than the males. The head and abdomen of the giant resin bee are black. Dense yellowish-brown hairs cover its thorax. Their wings are dark, but still transparent.

Season
June to september in North Carolina.

Life Cycle
The female bee nests alone and begins by preparing a cell in an existing tube or narrow cavity, using resin and sap collected ... read morefrom trees. Other materials such as bits of rotten wood and mud are also used in nest construction. Next she collects pollen and carries it to the nest on the underside of her hairy abdomen.

After completing several pollen collecting trips, she lays an egg on the pollen ball in the cell. Then she seals it, and prepares another cell. Continuing in this fashion, one female can complete about 10 cells. If the entrance of the nesting tube is directly exposed to the outside, the tube may be noticeably sealed with a resin, wood and sometimes mud cap. After the eggs hatch, the larvae feed on the pollen and spend the winter within their cells. The larvae pupate in late spring and the adult bees emerge that summer.

Remarks
They are opportunistic and nest in existing wooden cavities, rather than excavating their own.