Why Are There Dead Bees and Pupae in Front of My Hive?

One of the most unsettling events is to walk up to your hive and see dead bees or pupae littering the entrance or the ground underneath the hive. In some situations, this can be normal, while in others it’s a very sad result due to a number of factors.

Dead adult bees: It’s common to see a few dozen adult dead bees in front of your hive. However, it’s almost always indicative of a bigger issue if you see hundreds. Bees have a short life span, so bee death occurs every day at certain times of the year. Anytime a bee dies inside the hive, it is pulled out and thrown in front of the hive. On warm winter days, it’s common for workers to pull dead bees out of the hive. At any time of year, however, this should result in only dozens of dead bees, not hundreds. 

Possible causes of hundreds of dead adult bees:

1. Starvation: A starving hive, primarily in the winter, will result in hundreds of dead bees. Quickly look at your hive, even if it’s cold, and assess their food stores. If they are out of honey during a warmer season, feed immediately. If it’s cold, see “Late Fall and Early Winter Feeding.”
2. Significant Varroa infestation: Hives dying from Varroa mites will quickly lose the adult bee population. Test your Varroa levels. If they are above two to three mites per 100, you need to take action, but that’s not enough to cause a significant amount of adult bee death. If your mite count is in the teens or above per 100 bees, that could be the cause of the die-off. Quickly treat the hive, taking into consideration the time of year and your options.
3. Pesticide sprays: If your hive has plenty of food and low Varroa mite levels but still has hundreds of dead bees, it usually means they were sprayed. In this case, there isn’t much you can do other than let them recover with time. You can give them small amounts of syrup mixed with an essential oil or probiotic mixture and a few ounces of pollen substitute to help them, but usually they have to recover on their own. One way to tell if your bees died from poisoning is to see whether their proboscises (tongues) are sticking out and wings spread wide. Poisoned bees often exhibit these symptoms.
   
4. Too cold: If a small or weak hive gets too cold, adult bees on the outside of the cluster can die, resulting in hundreds of dead bees in front of the hive or on the bottom board. In northern climates where extended extremely cold weather is prevalent, it is expected that, on the occasional warmer day, workers will break cluster and remove the natural die-off. If snow is on the ground, it can be a bit unnerving to all of the sudden see a few dozen dead bees showing up on the bright white snow. It is, however, just part of the process of keeping disease out of the hive.

Dead pupae: It’s not as common to see dead pupae in front of hives. If you see only one or two, pay attention during your next inspection to see if there are more. If there are dozens, it indicates a problem. 

 Possible causes of dozens of dead pupae:

1. Starvation: If the hive has larvae or pupae and has almost no honey stores, they will cannibalize brood or pull them out of their cells if they can’t feed them. If your hive is almost weightless, this is probably the cause. Feed them immediately according to the season (thick syrup for cold weather or thin for warm conditions). 
2. Significant Varroa infestation: Like dead adult bees, finding an abundance of dead pupae could be from an overinfestation of Varroa mites. Testing and treating as mentioned above is your course of action.
3. Chilled brood: If brood gets too cold, it will die and workers will remove it. This is typically seen in three circumstances in the spring when nights are chilly but not during winter.

1. In early spring as the amount of brood outpaces the number of adult bees available to warm it—usually only see this during a more severe cold front

1. After splits when sufficient adult bees were not given to the split to keep the brood warm

1. After a hive has swarmed, leaving insufficient bees to keep the remaining brood warm

In any of the above cases, bees pull the dead larva out of the cells once it dies.  

4. Pesticide sprays or mite treatment: This is a bit rarer, but if a fumigating mite treatment is put in a hive when the temperatures are extremely hot, it can cause some brood death. Some fungicide and pesticide sprays that make it inside the hive or are in pollen that is fed to developing bees can also cause brood to die. Feeding Global pollen substitute can help give the bees an alternative protein source as they work through the contaminated pollen.