Bees crawling around on ground out front a hive can be only a few things.
- starving
- poisoning at forage site.
- disease or pest. Examples are virus such as xBPV or pest trachea mite, that mini tracheal mite is rare nowadays due to varroa mite controls also killing it but the tracheal mite can still be prevalent and show up in hives not treated for varroa.
- temporary ailment, eg: nosema, dysentery, poor nutrition (eg fermented syrup) can ground them until the pipes are purged and they feel better
- cool temperature, particularly at ground level. Chilled bees cannot fly. Heavy loaded bees coming back from foraging that miss their landing or land to rest, get chilled in low lying cold air near the ground, cannot get up.
To figure which you have there:
- Scoop up a handful of these bees. Put them on the lid of a hive in the sun and watch them. If they get active in a few minutes and readily fly away once they warm up, there it is; chilled. If after 5 minutes they are still crawling and difficulty flying, then your hive is sick and needs attention.
- also try holding a bee down and lightly squeezing the mid area of her abdomen down against the lid. Works best if she is lying on her side. Do not kill her, just apply steady pressure. If clear liquid oozes out of their mouth, there is a flow on and they are fully loaded. If streaks come out the other end of the bee, they are sick with belly aches. If nothing comes out either end, they are likely sick with a virus or poisoned.
- check the resources inside the hive. Ensure they have plenty of food (honey/pollen) to ensure they are not starving.
Lastly, be conscious of the season to determine whether to be concerned or not. At end of the summer the large mass of the old worn out summer bees dies off. Mostly they fly away and do not come back. If flight weather is poor they crawl out or are tossed out and expire on ground in a light carpeting out front. 1000+ old bees a day would be normal at that time of year.
Hope that helps.