Tree Bumblebee Life Cycle

The Tree Bumblebee

The Tree Bumblebee Life Cycle is quite a short one. It usually lasts from March until early July. These bees are very aggressive in defence of their nests. Tree bees are also very sensitive to vibrations in and around the nest. The bees will attack and sting to protect the nest often without provocation. It is advisable that if you believe you have one in a bird box, or around the soffit area of your house, to stay away from the nest area. Normally you only notice these bees when the drones start swirling and dancing around the entrance to the nest. Some of the information on this page is based on my observations and thoughts while dealing with Tree Bumblebees in a pest control capacity.

Tree Bumblebee

Tree Bumblebee
Tree bumblebee

Tree Bumblebee Synopsis

The “Tree Bumblebee”, “Tree Bee”, “Russian Bee” (Bombus hypnorum) is a recent addition to the UK. comes from the forests of Siberia and has spread throughout Europe. It was first found in the UK in 2001, in Landford, Wiltshire and is now present in most of England and much of Wales.In 2013 it reached southern Scotland.  The Tree Bumble Bee probably came to England in a container of goods. This is one of the first bumblebee species to be seen in the spring. This bee has spread quite rapidly, the reason for this is that the nest life cycle starts in March/April and has finished in early July leaving next years Queens to forage and increase their area before they go into hibernation. Native bumblebees nest life cycle ends in September and the Queens from these nests need to go into hibernation quite quickly.

My own personal view for this is that as the bees come from Siberia originally, which has a short summer, the bees have had to have a quick life cycle.  In this country, they awaken from hibernation in late March and the nests start to die off in late June early July. Also, the Siberian winter will kill off a lot of Queen bees due to the deep cold and length of time the Queen bees need to hibernate for. Our winters do not decimate the numbers of Queens, in the same way, leaving a lot more of them to procreate the next year. Consequently, this is a hardy bee and can be seen even on cold days.

Tree Bumblebee
Tree Bee Identification

Tree Bumblebee: Identification

Bumblebees can be identified from the colour patterns (banding) on their fur. Bombus hypnorum’s banding is unique amongst the UK species.The thorax can be yellow through to reddish brown, the abdomen is black and tail is white or grey. This colour banding makes this bee very easy to identify along with its size. Queens, workers and males all have a similar colour pattern but they differ in size.

Tree Bumblebee Life Cycle

The Tree bumblebees awaken from hibernation in March or early April and set about the task of finding a nest site. Unlike our native bumblebees which are predominantly ground-nesting bees, this bee likes to nest above ground. The Queens do “nest searching flights”, looking for somewhere snug to set up home. With this species, the flights are often along vertical surfaces of your house. In woods or forests they would normally choose a hole in a tree (hence the name Tree Bees) but in the UK they are very much at home in residential areas, bringing them into close proximity with humans.
Typical nesting sites are bird boxes, the soffit areas on a house, holes in a wall and occasionally compost bins. Over the spring of 2017, I have encountered tree bee nests in the ground. Tree bumblebee will often use old birds’ nests, the insulation in lofts and even old wasp nests. Indeed I have seen Tree Bumblebees and Wasps using the same entry point into a cavity wall.

Tree Bee Nest

Tree Bee Nest

Once a nest site has been identified the queen starts constructing the wax pods and lays an egg in each one. The nest is a collection of wax pods built haphazardly, intertwined in the nest are bits of straw and grass clippings. One of the pods is used to store nectar from flowers giving them a small food supply.
The Queen starts the task of raising the young until they are ready to take over the duties of caring for the nest and foraging for food. A typical nest can have between 150 to 400 bees in it at its height. Some of the workers grow quite large much larger than our native bumblebees and can easily be mistaken for queens.
Tree bees are very defensive of their nest and will sting if they perceive a threat to it. Unlike a honeybee, the tree bumblebee can sting multiple times similar to a wasp. They are also very sensitive to vibrations in and around the nest area. If you have a tree bee nest on your property be sure not to disturb it or get too close, remember they will sting often without provocation.
On a side note over the course of my work in pest control, I have met people who have been stung by these bees. Every time the sting has been around the face, including one I received on the ear. This suggests they follow the carbon dioxide in your breath. A tip for you, if you are being chased by tree bees try and hold your breath it may just help you avoid being stung.
The nest continues to grow through April and May and at some point from the middle of May onwards new Queens and Drones are produced. I am not sure what exactly happens, but in our native bumblebees, worker bees start laying their own unfertilized eggs. These eggs will become drones.The Queen then kills the grubs from these eggs, causing the workers to attack the Queen and eventually kill her. This allows drones to be produced and with the Queen dead the remaining eggs she has laid become Queens.
The drones then leave the nest never to return their only function now is to mate with Queens from Most people don’t know they have a Tree Bumblebees nest on their property until they see them dancing or swirling around the entrance to a nest. If you look carefully you can see other bees going to and from the nest these are ordinary workers carrying out their daily tasks.
The drones can’t sting but they can look formidable with up to 30 joining in the dance. The virgin Queens give off a pheromone which attracts the drones. Again if you look carefully you can see the drones flying between nests looking for an opportunity to mate.

The process of mating is actually quite savage, the drone jumps on top of the Queen as soon as she leaves the nest (she can mate with multiple drones). Once a drone has mated he dies. The reason for his death is that when he mates with a Queen he inserts his endophallus (bee penis) in her. The endophallus then breaks off killing him. Underneath the nest, you may find dead bees these are drones which have mated and expired. The Queen keeps the endophallus inside her ready to fertilize next years eggs.
Once a virgin Queen has mated she will build her body reserves up and then hibernate ready for the next year’s cycle. This is the main reason they have spread so rapidly the nest has died in July and the surviving Queens have the rest of the summer to expand their area, unlike a native bee where the nest will only die in September or October. On a few occasions, these Queens will start another nest.

Tree Bumblebee Predation

Bumblebees and honeybees are open to predation by the Wax Moth. I have seen wax moth grubs inside a tree bumblebee nest. The wax moth lays its eggs in the nest, the grubs eat the wax and grubs of the host bees. The Pied Hover Fly uses a similar technique only it attacks a Wasp nest. I have not seen Pied Hover Flies inside a bumblebee nest. Wasps will attack our native Bumblebees and Honey Bees and as mentioned earlier I have seen both Wasps and Tree Bumblebees using the same entrance hole to access the nest.

Tree Bumblebee Final Thoughts

Because this is a relatively new bee to the British countryside we still have a lot to understand about its habits and life cycle. I know a few beekeepers who are not happy about this bee mainly because they get a lot of phone calls about it. If you think about non-native species (grey squirrel, mink, American Signal Crayfish, etc ) they usually become a problem to our native wildlife. Only time will tell with The Tree Bumblebee. It is becoming a very common bee and we don’t know if it will have any impact on our native bees.

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Please visit  The Wasp Expert to view incredible videos of wasps and their life cycle.