Bumble Bees by Becky Colwell, Master Gardener

Posted by on January 16, 2019

Bumble Bee
all photos by Becky Colwell

Years ago I would see bumble bees in my yard, then they seemed to disappear. So, three years ago when I started noticing them again I was excited to see their return. This led me to doing a little research. Bumble bees, genus Bombus, are in the order Hymenoptera (bees, wasps, ants), family Apidae along with honey bees, carpenter bees, squash bees, southeastern blueberry bees and cuckoo bees. They are also ground nesters but are not totally solitary like the other native bees. I think this is one of the most interesting facts about bumble bees.


They are a semi-social bee having a colony during the summer months and then becoming solitary during the winter months. Here’s how it works: When the young queen comes out of hibernation in the spring she looks for a nest which needs to have several cavities, such as an abandoned mouse or other rodent nest. Inside the nest she starts preparing for her brood by building wax pots that she fills with pollen and honey. Then she builds a bigger cell for her brood. So in the early spring the bumble bees you see are the queens foraging to get their nests ready for her egg laying.


Queen Bombus nevadensis

Here is a queen Bombus nevadensis foraging at Huffaker Hills trail collecting pollen & nectar from sierra onions in early May. Once her nest is readied she begins laying her first brood, about 6 eggs that will become sterile female worker bumble bees. Until these workers emerge the queen will continue to forage. After the workers take over foraging, the queen remains in the nest laying eggs while the workers take care of everything else to keep the nest alive.


As summer begins, the bumble bees we see are the workers, which are smaller than the queen. The life span of a worker bumble bee is only a few months. All summer long the queen stays underground laying eggs to add workers for the survival of the nest. The colony can grow to about 200 worker bumble bees through the summer.


When summer is ending, the queen lays male eggs as well as female eggs. These female eggs become queen bumble bees and will mate with the male (drone) bumble bees. All of the worker bees, the old queen and drones will die at the end of summer. Only the recently mated queen bumble bees remain and will sleep in secluded hideaways through the winter. Next spring the queen will emerge and start establishing her colony for the next generation of bumble bees.


So now as we enter fall, the only bumble bees you are likely to see would be the recently mated females fattening up on pollen and nectar to get them through the winter months – as the bumble bee in the photo is doing visiting my butterfly bush at the end of September.


Another interesting fact about bumble bees is that they are very effective at pollinating tomatoes due to their buzz pollination. Large greenhouses that grow tomatoes year round use queen bumble bees to keep us in tomatoes. All they need to do is provide the queen with a box for the nest, a supply of sugar water as tomatoes only provide pollen and let the bumble bees fly freely within the greenhouse. So the next time you’re eating tomatoes in the middle of winter, be sure to thank a bumble bee.


Reference:
Bee Basics An Introduction to Our Native Bees; by Beatriz Moisset, Ph.D and Stephen Buchmannm, Ph.D.; A USDA Forest Service and Pollinator Partnership Publication.

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