Wintering Bumblebees

[Dan Williamson]

Someone called me a couple of days ago with several bumblebee hives that they purchased for pollination of their blueberries. They wanted to know if I wanted to try to winter some of them. I know NOTHING about wintering bumblebees.

I don't have time to go get a book and do alot of self-educating about this as she wants me to do it now!

Can someone give me a quick tutorial on what it takes? Do you refrigerate them or how do you handle them?

I'm completely ignorant.

[Kieck]

Short version: you don't overwinter bumblebee hives.

Bumblebee queens live a single season, and they "found" (start) new colonies each spring. To overwinter bumblebees, you need to refrigerate mated, new queens. In the spring, you attempt to confine them to the domiciles (hives) until they get enough comb started that they're likely to return when they're given their freedom. Obviously, while you have them confined, you'll need to provide them some honey and pollen.

But, if the colonies are free, you could take them and leave them outside over winter. Often, new queens (maybe not the same species, but bumblebees all the same) will find old nests and use the materials available to start a new colony.

[Dan Williamson]

Short version: you don't overwinter bumblebee hives.

Bumblebee queens live a single season, and they "found" (start) new colonies each spring. To overwinter bumblebees, you need to refrigerate mated, new queens. In the spring, you attempt to confine them to the domiciles (hives) until they get enough comb started that they're likely to return when they're given their freedom. Obviously, while you have them confined, you'll need to provide them some honey and pollen.

But, if the colonies are free, you could take them and leave them outside over winter. Often, new queens (maybe not the same species, but bumblebees all the same) will find old nests and use the materials available to start a new colony.

So I'd need to find the new or A new mated queen and try to refrigerate them. I don't even know what this lady has... I just know she paid $1200 for bumblebee colonies and wants to try to overwinter them. I think she only knows slightly more than I do....

[Kieck]

Right. Bumblebees produce new queens late in their season. For "early-season" bumblebees, new queens may appear as early as July.

Once the new queens appear, they mate with the males. The mated queens will attempt to overwinter.

After producing the new queens, the old queens die. The workers eventually disperse, although they may remain more-or-less loyal to their nests for a period of time.

Following a period of dormancy (also known as "winter" around here), the new queens attempt to locate suitable nesting sites, set up a "honey pot" and a few cells, and start raising workers. Unlike honey bees, while the queen (the only one -- she has no workers at this point) is establishing the colony, she must do the foraging for her larvae. She provides all the care, she collects all the pollen and nectar. Once the first workers emerge (typically, these workers are much smaller physically than later workers), they take over some of the brood-rearing duties, particularly foraging. In some cases, though, queens will continue to forage periodically along with their workers.

The real trick in trying to manage bumblebees is convincing them that the domiciles (hives or boxes or whatever) that you provide are suitable nesting sites. Some queens will use them. Some will abandon them as soon as you provide an opening for them to leave. And some will simply wander around and around in their confined space without ever becoming "broody" and trying to start a colony.

[Dan Williamson]

Interesting...

So the new mated queens will not stay with the original nest? She will move on and look for another location? I was thinking (probably wrongly) that at least one newly mated queen would stay with the same nest and start up a new colony come spring.

I'm thinking I'm way over my head on this one.... I should probably tell her I don't know enough about it to attempt it.

[Kieck]

If the original location is "good" enough, future queens will likely reuse it. However, those queens are just as likely to have come from other nests as from that location.

If the location is protected enough, a queen may attempt to overwinter in it.

However, those queens run a terrible risk. The minimum openings to bumblebee hives must usually be larger than minimum openings to honey bee hives. That leaves them vulnerable to mice, and other creatures. Now add a little honey to that, some dried leaves and other materials, and some fatty insects (bumblebees, either in the form of maybe a few dead workers or a new queen or two), and those places attract rodents like nothing else.

To make it even worse, the scent of mouse or other small rodent urine actually seems to entice queen bumblebees to select sites with the smell as nesting sites. Bumblebees often nest in old mouse nests or squirrel nests or similar rodent homes. So rodents might be even more likely to move back in. If it was suitable for rodents once, it likely will be again.

If the woman is giving you the hives, I recommend giving it a try. Just let her know that it's unlikely that the bumblebees will re-establish colonies in those hives. What have you got to lose? (And, as someone who keeps some bumblebees, the experience can be amazing.)

[Dan Williamson]

So would you recommend finding a place and leaving the nest in a sheltered spot or trying to refrigerate and then place out in the spring?

[Kieck]

I would simply leave the nests outside (in some sort of sheltered spot). If some new queens were readily at hand, I might try carrying them through diapause (dormancy) -- but let me warn from experience that doing so is more difficult than it may seem. Temperatures must remain low enough to sustain that diapause (once they "break" diapause, they are unlikely to become dormant again), and moisture control is a huge issue. Too wet, and the queens are likely to die. Too dry, and they die as well.

For diapause conditions, if you try it, five months at 35-40F (2-5C) with 60% relative humidity seems to work well. Diapause of three months or less will likely require the artificial use of carbon dioxide to cause the queens to break dormancy.

[Dan Williamson]

Thanks Kieck. I don't have the resources to try to winter them at controlled temps and humidity.

Managing bumblebees is something I want to learn more about. I need to get a book and check into it better. I have some outbuildings old hog sheds that might be good places to try placing some nests in.

Thanks again for the info.

[MichaelW]

According to Delaplaine's ABJ article, you should be able to place the boxes in an unheated building, at least 10X10 with one window. Put out a feeder. Pollen may or may not be necessary?. The virgin queens will mate within the building. Sounds like you would have plenty of bees for diversity. Below the window put a small pile of leaves. The mated queens will congregate at window and end up burrowing in leaves to over winter. Collect mated queens in vials to overwinter in fridge use those to start.

I wouldn't recommend "releasing" the bees as they often carry diseases not present in native populations. You also may be introducing a non-native bumblebee species.