Updated: 8th February 2021
Finding dead bees can cause concern, but
if you have found dead bees in your yard, garden, beneath a tree or
simply on the pavement, there are various possible
explanations, depending on the species and circumstances.
Sometimes, the causes are natural rather than sinister. All creatures live then die, either due to age, disease, weather, natural predators and so on. If you are concerned about pesticides, please see the links at the bottom of this page.
However, most individual bees have very short life spans – some species as little as a few weeks. The only exceptions within a colony are the queens. You can read more on my page: How Long Do Bees Live?
In my experience, the majority of people tend to report specifically seeing dead bumble bees, that is, with the exception of beekeepers, who report dead honey bees – we’ll get to that in a moment.
If you have found dead bees – usually up to around ten, all within a confined area, and you believe they are bumble bees, then most commonly this is part of the normal bumble bee colony life cycle.
Individual bumble bees may die in the nest from time to time. This could happen due to being fatally harmed whilst defending the colony against a predator visit. It could be down to age or disease. When this happens, other members of the colony will clear out the dead members from the nest in order to preserve hygienic conditions within the nest1.
This results in a noticeable handful of dead bees around the same location. Although there will be a nest nearby, you may not have noticed it - yet, so have a look around.
Bumble bee nests can feature in a variety of places: high above ground (even in bird boxes), but also underground in abandoned rodent holes, or in clumps of grass.
One year, my sister found dead bees by her pond. When I asked her for further information, it turned out they were bumble bees. They had made a nest by the water’s edge, and on closer inspection, the dead bees were found around the entrance. More than likely, the bees had been removed from the nest as part of normal hygienic activity on the part of the colony.
All this may seem rather sad, but it is worth remembering that at the end of the season, only the new bumble bee queens will live and establish new colonies the following year, whilst the rest of the bumble bee colony will not survive. (A few exceptions are being reported and there are differences in some warmer climates).
If you have found many dead bees around the base of a tree, check whether the tree is a lime.
To quote an excerpt from 'A Sting In The Tale' by Professor Dave Goulson (also author of Bumblebee Behaviour And Ecology):
So it seems some lime trees (notably non-native ornamental species,) are toxic for bees – or at least have narcotic effects, with some species of lime believed to be more harmful for bumble bees than honey bees.
Other Dead Insects?
Alternatively, has the tree been sprayed with pesticide? If so, it could be a case of acute poisoning (rather than chronic poisoning), and you may see other dead insects around the same area.
If you suspect poisoning, I recommend you collect evidence – dead specimens, photographs, and any information you can about the use of pesticides at the location, then report it to your local authority, or health and safety directorate. Some countries have specific places where wildlife poisonings are meant to be reported – check this with a relevant government body. Neonicotinoid pesticides are a particular cause for concern.
Have you found a dead bee (a single specimen), perhaps on the ground or even on a plant? Again, the reasons could be perfectly natural, for example, because of the age of the bee, or due to predator attack or internal parasites or disease.
Some bees can be mistaken for dead, when in fact they are resting or sleeping.
If you find a whole
colony of dead bumble bees – i.e. in the nest, then it is likely that this is
due to the invasion of a predator or parasite, and there may be visible signs
of this, such as silky webbing (wax moth).
If you come across an infested nest, sadly, there is generally little you can do to help the bees at this stage.
I have written separate pages for the following:
bumble bees with missing head or body
Honey bee colonies are meant to survive the winter (see Where Do Bees Go In Winter.
However, finding a few dead honey bees is perfectly normal. Again, dead bees (due to natural causes or disease) are automatically removed from the nest or hive as part of hygienic behaviour, which is triggered via a 'death pheromone', oleic acid which is emitted by dead colony members, and detected by live workers2.
During the winter, there will usually be more casualties, and this is known as ‘winter mortality’.
Sometimes, honey bee colonies will succumb to inclement weather conditions during 'cleansing flights' - they leave the hive for a short while, but unfortunately they can get caught out if the weather suddenly turns against them. This was the case in the photograph at the very top of the page, when in fact, many bees were found dead as a result of a snow storm.
This is significantly different from the exceptional losses reported in recent years, with beekeepers losing around 30% of colonies or more due to colony collapse disorder (although this ‘condition’ is a term used to describe a number of phenomena, with variations in definitions and symptoms reported).
a system for recording collapses, and it’s important to record these
However, it is my personal view that the impact of pesticides should also be considered, since they may significantly weaken the colony and make them more vulnerable to diseases.
Although you may be saddened by the sight of dead bees in your garden or yard, the reasons are often natural. If you suspect other causes, it may a good idea to alert the relevant authorities in your area.
With regard to insecticides, it is best to avoid using these in your garden, including on your lawn, since they can poison bees, and indeed, may also cause harm to other beneficial invertebrates.
1. Bumblebees, Their Behaviour and Ecology. Goulson, D. (2003); Oxford University Press, ISBN 0-19-852607-5.
2. McAfee, A., Chapman, A., Iovinella, I. et al. A death pheromone, oleic acid, triggers hygienic behavior in honey bees (Apis mellifera L.). Sci Rep 8, 5719 (2018). https://doi.org/10.1038/s41598-018-24054-2
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