Bees consequently really do not like bees that come from other hives. We do get a weird phenomenon called drifting – when bees go out and collect nectar and pollen and come back loaded they can accidentally fly into the wrong hive.
A Quick Introduction To Why This Is Not As Easy As It Sounds
If you have a good strong hive, you can harvest young bees from that hive. These will often be on the edge of the brood nest or making wax in the supers. Look at the bees and if they are very fluffy, they are young.
How To Strengthen A Hive By Adding Bees To An Existing Hive
Dump all the bees from both hives in front of the stronger hive, put all the brood and pollen combs back in the one hive. With a bit of luck, the bees will combine. I find in my area this works about 80% of the time.