Bumble bees spend most of their lives underground

By Julie Banken
WSU Chelan/Douglas County Master Gardener

Bumble bee in underground home
Bumble bee queens spend the winter hibernating in shallow burrows in the soil. – Provided photo/Julie Banken
bumble bee on stick
Bumble bees are one of many species of native ground-nesting bees that play a vital role in pollination. They tolerate cool temperatures and are among the last pollinators at work in the fall. – Provided photo/Julie Banken
Julie Banken
Julie Banken WSU Master Gardener intern – Provided photo/WSU Master Gardeners

Last month, when my son and I were harvesting our potato crop, we were surprised to dig up a bright yellow bumble bee.

Bumble bees are known as creatures of the air, not animals that live in the soil next to earthworms. However, these native bees actually spend more time under the ground than above it. These “humble bees,” as they were once known, deserve recognition for the indispensable role they play in the garden ecosystem.

Bumble bee queens like the one in our potato bed spend the winter months hibernating alone in shallow burrows in the soil. After emerging in the spring, they establish their nests in empty cavities in the ground. Rodent burrows, rock piles, and vacant space at the bases of bunch grasses and sedges are their favorite spots.

Once a nest site is chosen, the queen gets busy. She flies from flower to flower for food, traveling up to a mile away from her home base, pollinating a wide variety of plants as she goes. She carries pollen and nectar back to her nest in the ground where she deposits it into tiny wax chambers appropriately called honey pots. The queen lays an egg on top of the food bundle in each honey pot, and, like a bird, will protect her eggs and even keep them warm until they mature into full-grown adults.

It takes about a month for the queen’s offspring to develop into working females. Once her daughters are able, they take over the tasks of the growing colony, allowing the queen to remain in the nest to lay eggs. The daughters care for the queen, build more honey pots, forage for food, store up provisions, and help care for the young. The more pollen and nectar they gather, the more daughters the queen can produce. By the end of the season, colonies have on average 50 to a few hundred bumble bees living and working in their underground home.

In the fall, male bees emerge along with new queens. The social life in the colony comes to an end as winter approaches. Every bee in the colony dies, in fact, except the young, newly mated queens. They dig new burrows in the soil and remain underground until spring, when the cycle starts all over again.

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Honey bees get all the glory, but wild bees like the bumble bees are actually more efficient pollinators. They can fly in temperatures as low as 45 degrees Fahrenheit, so they are able to pollinate the first flowers that bloom in the spring and the last flowers that bloom in the fall. They are also able to do something honey bees can’t do: they vibrate their wings until a flower gives up its pollen in what’s called “buzz pollination.” Tomato, potato, and blueberry plants require buzz pollination to create their fruit.

Bumble bees are not the only bee species to live underground. There are over 400 native ground nesting bees in Washington alone, including alkali bees, sweat bees, digger bees, mining bees and plasterer bees. Unfortunately, many of them are threatened or at risk of extinction due to habitat loss and exposure to toxic chemicals in the environment.

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Home gardeners can play an important role in protecting our native bees by providing them an inviting place to live and work.

Here are a few ways to make your landscape bee-friendly:

  • Avoid tilling the soil in the fall. Harvest your potatoes early!
  • Incorporate a wide assortment of flowering plants into your landscape so the bees will have food throughout the spring, summer and autumn. When deciding what plants to add to your yard, remember that native bees like native plants best. Visit the Pollinator Garden at the Leavenworth Fish Hatchery in person or online for ideas.
  • Leave the leaves that fall in your garden and flower beds to provide cover for the insects living below.
  • Create nesting habitat for ground nesting bees by not using plastic or fabric weed barriers. Instead, apply layers of organic mulch to keep weeds at bay.
  • Above all, keep your yard free of toxic chemicals found in herbicides and pesticides. If the label says “systemic,” then the poison intended for pest insects will end up inside of plants’ pollen and nectar, and ultimately will be ingested by pollinators and fed to their young. Avoid the risk of inadvertently introducing harmful chemicals into your yard by purchasing plants from nurseries that do not use systemic pesticides.

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A WSU Chelan and Douglas County Master Gardener column appears weekly in The Wenatchee World. Julie Banken is a Master Gardener intern. To learn more, visit bit.ly/MGchelandouglas or call (509) 667-6540.