Among other things, I am a beekeeper... First step is to identify what you have. Honeybees tend to make LARGE colonies, with lots of bees coming and going at the same time. However they are generally quite mellow unless you are seriously in their flight path, or are disturbing the hive - I can stand next to my hives and watch the traffic w/ no gear and no problems - I've also run around with the weed whacker directly in front of the hive entrance, again no issues.... However if you go rapping on the side, you are likely to get nailed, and when they sting, it releases a pherome that tells the other bees "Enemy here - ATTACK" so you may get multiple stings if you get any... (If attacked, leave the area rapidly, and attempt to break the line of sight - go through some bushes or around a corner to get out of sight of the hive.)
Honeybees are typically fairly small, about 1/4"-1/2" long, and will generally have a banded tail, alternating dark gold and black to solid black - they will have a visibly fuzzy thorax (where the wings attach) Bumble bees and carpenter bees are much larger, tend to be fuzzy all over, and have a brighter yellow and black coloration. They also tend to be fairly non-agressive.
Wasps and yellow jackets often, but not always, have a bright color pattern, and will generally be smooth with little or no "fuzz" - they tend to be very agressive. The difference is that bumble and honey bees are vegitarians by nature, and sting only as a last resort or to protect the hive - stinging is fatal to a honeybee so its the last thing in the world she wants to do. (Only the sterile female worker bees will sting - the males can't) Thus the only time a honey bee will sting is if it feels trapped (i.e. you are stepping on it) or if you are trying to get into the hive...
Wasps and yellow jackets are predators, and the sting is part of their hunting equipment - they can sting as many times as they want to, so they tend towards what I call the "Dirty Harry" attitude - "go ahead, make my day" They are more likely to be ground nesters though.
If they are honeybees, they are extremely valuable to have around, and are generally protected critters, you don't want to kill them if at all possible. At the same time they probably aren't great to have in a kid's play area. Some beekeepers will be interested in catching them to put in a hive, others may charge you. The important thing in either case is to get all the bees you can, and to block up the entrance so that it's no longer a potential home for another swarm to move into...
If they are not honeybees, pesticides are a good idea, the other varieties aren't terribly useful to humans, and aren't endangered...
Given that you say they are nesting in the ground, I'd be inclined to think they are some sort of wasp or yellow jacket, possibly something like a bald-faced hornet (hornets are also NASTY....)
As to the stuff they are carrying back to the nest... If they are predatory, it is likely catapillars or other insects that they have killed and are bringing home to raise their young on. If they are honeybees, it is likely pollen.
Honeybees collect pollen as they go from flower to flower. They scrape it off and pack it into structures called "pollen baskets" on their hind legs. They bring it back to the hive in these baskets, so when they land, it looks like they have a pair of footballs on their hind legs (and the pollen balls are about that scale) These pollen balls can vary amazingly in their color, depending on what kinds of plants the bees are foraging on - I've seen white to yellow, to green, red, and even black...
If you have the room for it (and it doesn't take much) beekeeping is one of the easiest forms of animal husbandry there is, and it's a very useful thing to do as it will greatly increase the yields of all the flowering plants and vegetables in your area - about 1/2 the stuff you see in the grocery store is pollenated by honeybees... (and locally produced honey is much better for you than the over processed store bought stuff...)
Gooserider
