I came across this guide on how to differentiate between Bees and Wasps.  I have been planting flowers for the past year to attract bees and starting noticing different types of bees.  Lo and behold, possibly half of the ones I was observing were actually wasps.  PS.  Wasps are beneficial insects too, since they eat pests.  I learned quite a lot from this UC Berkeley guide below.  Enjoy!

From: http://nature.berkeley.edu/urbanbeegardens/list.html

Bees Vs. Wasps

Many gardeners and other urbanites often refer to bees and wasps interchangeably. As you become familiar with the organisms in your yard environment it is important to learn to distinguish bees and wasps as each of these insect groups has very different lifestyles. Bees are interested almost exclusively in pollen and nectar from your plants, and they are adapted evolutionarily to use these specific plant parts for energy (nectar) and to provision their offspring (pollen plus nectar). Wasps, in contrast, are mostly predatory and visit your garden searching for small prey items like caterpillars. Occasionally, small slender wasps can be observed taking nectar from selected flowers only, for example, from species of Eriogonum (shown at right), the buckwheats. In almost every case, these are beneficial wasps looking for a drink of nectar. They have no interest in the pollen. In fact, they don’t have body parts adapted for pollen transport as do bees.

The yellowjacket wasps (see above photo) are most often confused by urbanites. Yellowjackets are not bees! These wasps are predatory in habit, which means they hunt and feed on other living organisms, mostly other insects. Often, they fly around plants and even land on flowers where they look for prey items such as caterpillars. However, these wasps have also taken a liking to human food, especially meat and soft drinks. You may have already noticed that encounters with yellowjackets usually occur whenever we eat food outside. We can guarantee that you will never see an authentic bee eating a burger or hot dog.

If you study the photos in this website you will begin to be able to distinguish between bees and wasps. Note especially the great amount of fine hair found on almost all bees in contrast to the sparse hair on wasps. It is their hairiness that makes bees so important to pollination and plant reproduction: these hairs are designed to pick up pollen and carry it from one flower to the next.

Finally, as mentioned elsewhere in this website, female bees and female wasps have stingers that are used in defense. Some wasps species also use their stingers to paralyze prey items, which are then used directly for adult food or later for food for their offspring, in the case of social wasps. When close human encounters with bees and wasps occurs, stings may result but this almost always happens when the insect feels threatened. This is even true in the case of the famous Africanized honey bee (or killer bee), which behaves more aggressively than most other bees and wasps in defense of their hives.