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If you see a bumblebee now, it is most likely a common eastern bumblebee (Bombus impatiens), which are remarkably resilient: While most other bumblebee species are done for the season, with newly hatched and mated queens overwintering in or on the ground, waiting for spring to reemerge, this one forages on. It can be seen until November, if the weather stays warm enough. Even during summer droughts, when other bee populations shrink, common easterns persist.
Late in the summer or early fall, the queen bee in a colony lays fertilized eggs that are nurtured to become the next generation of queens. She also lays unfertilized eggs, which grow into male bees. When the male bees emerge, they have one job: to mate with a new queen, so she can produce the next generation of bees in the spring.
The new males and queens leave the colony and search for partners from different colonies. The males never return – you might spot one sleeping on flowers in late summer – and die within a few weeks. The females return to their original colony for food and safety. They search the terrain for any remaining blooms to help build up their winter fat reserves and live for about a year if they successfully start a nest in the spring. The worker bees in this year’s nest begin to die off as the temperatures cool and food decreases, though. Soon the old queen dies, too. All that’s left of the once-thriving colony are a few young queens who must survive the winter and start a new colony in the spring.
A colony often produces 10 to 20 males and queens. Once mated, the queens (carrying fertilized eggs) dig a shallow hibernation chamber in which to overwinter. Then the queens enter diapause (dormancy) by synthesizing alcohol molecules – think of it as bee antifreeze – to protect their cells from freezing. For common eastern bumblebees in Massachusetts, this slumber lasts for about four to six months beginning as late as mid-November and ending as early as mid-March; other species of bumblebees are dormant for up to nine months. A 2024 study showed that overwintering bumblebee queens can survive underwater, if the ground becomes flooded, for a week.
A queen bee becomes dormant quickly – about two weeks after reaching adulthood. She doesn’t want her body to age much. A queen and her sister queens often overwinter near the original nest. If one of the queens survives to begin a new colony in the spring, the colony passes on its genes to a new generation.
The queens emerge from dormancy in the spring when nighttime temperatures are warmer than 35 degrees Fahrenheit. The queens forage on nectar (sugar) for energy and look for a place to build a nest. If you see a bumblebee in spring flying low over the ground, stopping to explore crannies and burrows, you are probably seeing a queen looking for a good place to build a nest – often an abandoned mouse or chipmunk burrow.
Once a site is selected, the queen stockpiles pollen. When she has enough, she lays her first batch of eggs. The eggs hatch in about four days, and small female larvae (grubs) emerge to feed on the stockpiled pollen. The larvae grow, shedding their skin several times, for about two weeks, then spin cocoons. Inside, pupae develop for another two weeks. They emerge as full-sized female worker bees to begin collecting and storing pollen and nectar. These workers have underdeveloped ovaries, so only the queen can produce more offspring.
The queen now stays inside the colony, focusing on laying more eggs to increase the size of the colony. The colony grows throughout the summer. How much it grows depends on how plentiful the pollen and nectar is for eating, but it can potentially grow to 450 bees. In late summer or early fall, the queen lays the unfertilized eggs that hatch into males, stops producing worker bees and begins nurturing fertilized eggs into becoming new queens.
At first, the new queens stay in the nest and build up their fat reserves, attended to by workers. Soon the queens leave to forage and find a mate. They mate only once with a single male from among those patrolling the entrance to the nest waiting for a young queen to emerge.
Once the queens mate, the males die and the process begins all over again.
Late summer and fall is an important time for the young queens. They need to find enough flowers to build up fat reserves to carry them through the winter. The worker bees and queen from the original colony die as freezing temperatures arrive.
In spring, summer and fall, bumblebees help pollinate flowers by carrying pollen grains on its fuzzy hairs from the male part of the flower to the female part. Bumblebees are buzz pollinators: They grab onto a flower and vibrate their abdominal muscles, creating a buzzing noise and shaking free a large load of pollen. Some flowers need the buzz to release their pollen, but vibrating stomach muscles also generates heat that warms the bees – and because they can generate heat, the bumblebees can pollinate flowers at lower temperatures, lower light levels and in wetter or windier conditions than other bees.
Although common eastern bumblebees are easy to spot, native bumblebees that a decade ago were common in Massachusetts have become rare. Today there are only seven species in Massachusetts, down from 11 only decades ago. Three of these seven are at risk of disappearing in the next decade. You can help bumblebees by planting native plants that flower from spring to fall.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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