Depending on where your hive is situated, the ground in front of the hive may be smooth enough for you to spot dead bees there. This is not necessarily any cause for alarm.
During the spring and summer, the worker bees only live about 45 days. And, the queen can be laying 1500 to 2000 eggs per day that produce adult worker bees just 21 days later.
So, at some point in the summer, in any given colony, there are going to be hundreds, if not thousands, of bees that are dying a natural death each day.
The worker bees finish out their life as foragers. But, their wings are only good for about 500 miles of flight. So, eventually, they will make a foraging trip from which they are unable to return to the hive. Here is a photo of an older forager. You can tell this from how worn her wing tips are. See the chips in the edges of her wings?
Honey bees are extremely fastidious. They remove any bees that die inside the hive. And, you may even see them flying off with the carcasses so that the odor of dead bees does not attract predators like wasps or hornets.
If a honey bee is inside the hive, and knows she’s dying, she will do her best to crawl out so that the colony does not have to consume resources to remove her. This is even true of a queen, which I have seen with my own eyes. (An incredibly sad sight.)
So, some dead bees outside the hive entrance is completely normal and natural.
If you see a pile of dead bees outside the hive, however, it usually indicates that one of your neighbors used an insecticide or herbicide, and your bees unwittingly brought it back to the hive – on the pollen or in the nectar – and it poisoned them. All the poisoned bees then crawled out to die.
This is why poisons – even just spraying Round-up on dandelions – is so devastating to the earth. The poison doesn’t just kill the bees that visit those flowers; it can kill whole colonies because they transport that poison back to their hive before dying themselves.