There are about 250 known species of bumblebees worldwide, and around 40 of these Bombus species are native to North America. The US Forest Service and the Pollinator Partnership published this free online guide to Bumble Bees of the Western United States. It's a wonderful resource, although I must admit I'm still trying to identify the species in my own yard; we seem to have quite a few!
Bumblebees use a process known as sonication or "buzz pollination" to vibrate the pollen out of flowers. That rather high-pitched buzzing that bumblebees make when they visit a flower? That's the sound of sonication - To the naked human eye, it may look and sound like much ado about nothing, but there's an awful lot going on - The bees are vibrating their flight muscles to generate forces up to 30 G that loosen and blast pollen right out of flower species that hold their pollen close in anthers with tubes (poricidal anthers). Because of this, they're able to pollinate a number of food crops that honeybees, who can't sonicate, aren't able to access. Sonication is necessary to pollinate a variety of food crops, including eggplant, tomatoes, blueberries, and cranberries. Bumblebees are an increasingly important commercial-scale pollinator used by many farmers much more industrious than I. See this Leonard Lab web page devoted to Buzz Pollination for much more in depth information, and watch the video below for a quick education in sonication.
Bumblebees can sting, but they'll most likely choose not to. Until I started my Bombus research, I didn't know they could - They can, and apparently their stings are quite painful. They're such sweethearts by nature, I've been playing and gardening around them all my life without a single sting (something I can't say for the honeybees, yellow jackets, and wasps I've crossed paths with).
You can pet bumblebees if you're daring and respectful. You must use a very gentle touch, but you can stroke their fuzzy backs while they're at work on flowers. They'll put their hind legs on your finger if you're annoying them. Native Plants & Wildlife Gardens has safe bumblebee handling tips in this article. Bees have pretty high stakes sex lives. If you're so inclined, you can watch Isabella Rossellini's Green Porno episode about honeybees; much of this applies to bumblebees, too. In a bumblebee colony, each queen lives just a single season and sends out daughter queens as her last act, to sleep the winter away before waking in the spring to build their own colonies.
It appears that bumblebees are also suffering population losses, with some species like "Big Fuzzies" all but disappearing from their traditional ranges. The Smithsonian has more information in this article about what we know and what we still need to learn.
In better news, it's possible to invite bumblebee colonies to your own backyard habitat. Bumblebee.org has directions on building your own nest boxes and improving your hyper-local habitat to attract and support local bumblebee colonies. So, here's to bumblebees. They may not make honey, but their hard work brings us other delicious gifts. We need them and they need our attention and support.