A large cluster of bees hanging outside the hive at night can definitely be cause for a new beekeeper to worry. Afterall, why in the world are half my bees outside?! And it’s dark!
The good news is this is usually normal- just not something most beekeeping book mention.
Normal nighttime behavior
When it’s been a hot day, it can just be more comfortable for the bees to hang out (quite literally) outside. Imagine trying to rest in a hot stuffy house. Now imagine there’s a comfortable porch to rest on.
Some beehives don’t have good ventilation. Especially in these cases, the bees sometimes prefer to rest outside.
If there’s a high population, sometimes there is not enough room for all the bees to comfortably fit in their hive.
When it signals a problem
Bees hanging outside the hive in large numbers (for this application, anything larger than a baseball would get my attention) can signal the bees have poor ventilation, are struggling to keep the hive cool, or are overcrowded. Another thing to notice- Is this only happening on nights when the daytime temperature has been in the high 90s and 100s? Is so, this could likely simply be the cause of extremely high head during the day, and not something to be quite as concerned about.
How to reduce nighttime clustering
If the bees are overcrowded, add a super. This will give them more room inside the hive. You’ll know they are overcrowded when they have filled 7/10ths of their available space.
Improve the airflow in the hive. Consider using a screened bottom board, and a ventilated inner cover. If you have a solid or screened inner cover, consider wedging a stick between the inner and outer cover but only do this if the bees cannot get out the top.
Consider adjusting the hive placement. You want partial sun, especially in these cases morning. Full sun all day makes it harder for the bees to cool the hive.
For more information see my other posts about keeping bees in the heat.
Keeping Your Bees While on Vacation
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