The rusty patched bumble bee was added to the federal endangered list in March 2017. (Johanna James)

The Plight of the Bumble Bees
By Joan Schnabel
May-June 2017 Big River Magazine

A few years ago I heard Dar Williams sing a song called “Johnny Appleseed” by Joe Strummer. One line stuck in my head: “If you’re after getting the honey, hey then you don’t go killing all the bees.”

Substitute the fruit or vegetable of your choice for honey, and the advice is the same. And while it may seem obvious, apparently it’s not. Bees of all kinds, including honey bees and bumble bees, are dying in unprecedented numbers. Everyone who is fond of eating should be concerned. On March 21 the rusty patched bumble bee became the first bumble bee species to be placed on the Endangered Species List.
There are 21 species of bumble bees in the eastern United States. Bumble bees are native to North America, in contrast to the familiar, though imported, honey bees. Both kinds of bees gather pollen, a source of protein and fat, and nectar, a source of high-energy carbs. Bumble bees can also convert nectar into honey, but do so only in small amounts, just enough to get the colony through a few days of bad weather.

Although 90 percent of the bee species in the U.S. are solitary, bumble bees are considered “eusocial,” meaning they form colonies. Unlike honey bees, only young queen bumble bees overwinter, another reason they do not need to store large amounts of honey.

In the spring, lone queens emerge from hibernation. They forage to collect nectar and pollen, find a nest site, then begin laying eggs fertilized from sperm stored since mating the previous fall. After workers hatch, the queen stays in the nest. In late summer males and new queens hatch and disperse, the males to mate and the new queens to overwinter alone. Then the workers, the new males and the old queens die.

Shake that Abdomen!

Bumble bees are important pollinators. Without them we would not have tomatoes, eggplant, blueberries, cranberries and many other plants. These plants all require “buzz” pollination, or “sonication,” something honey bees can’t do. Buzz pollination requires a bumble bee to redirect her flight muscles from her wings to her abdomen and then contract those muscles to produce a strong buzz, or vibration, that shakes the pollen loose from a flower and onto her fur. She then grooms herself, moving the pollen into “baskets,” called corbicula, on her hind legs. Fortunately, the pollen she misses is carried on her body and rubs off onto the next flower she visits, pollinating a variety of wild plants and important crops.

Bumble bee populations are not doing well. The decline of several wild species began about the same time as the decline of commercially bred western bumble bees, raised to pollinate tomatoes and sweet peppers grown in greenhouses. The presumed cause was the Nosema bombi fungus, perhaps spread to wild bumble bees sharing foraging sites with commercially bred bees. And while correlation does not imply causation, the introduction of neonicotinoid pesticides parallels the precipitous decline in the bees. Studies of honey bees show that neonicotinoids applied to seeds have increased preemptive insecticide use. Bumble bees may be even more vulnerable than their cousins to toxins. In the spring there are no worker or male bumble bees. Each potential colony consists only of a queen who needs to go out to forage. If the queen dies, there will be no colony. Bumble bees nest in the ground exposing them to even more pesticides.

Common to Rare

The endangered rusty patched bumble bees, Bombus affinis, have completely black heads. Workers and males, but not the queens, have the namesake rusty-red patch in the middle of their backs. Size cannot be used to identify bumble bees, because a bumble bee’s size depends on the nutrition it received while it was a larva.

Rusty patched bumble bees originally lived in the tall grass prairies of the Upper Midwest and Northeast. They were found in 28 states, Washington, D.C., and 2 Canadian provinces. Since 2000 their range has decreased to 13 states, including Illinois, Iowa, Minnesota and Wisconsin, and one province. They are now inhabiting only about 0.01 percent of their original historic range, according to the U.S. Fish and Wildlife Service (FWS), which says they are “on the brink of extinction.”

The FWS estimates an 88-percent decrease in the number of populations (Populations of B. affinis consist of tens to hundreds of colonies.) and an 87-percent loss of territory. Historically there were at least 926 populations, but by 2000 that number was down to 103. Of those 103, many have not been reconfirmed since early 2000 and may no longer exist. In 2010 no bees were seen at 41 of the “current” sites, and by 2015 bees were absent from 75 of the 103 known sites. Although previous sites were known to have up to 1,000 bees, the maximum seen recently at any one site was 30, and 95 percent of the populations found had five or fewer bees.

Several factors contribute to this loss. As mentioned, pesticide use has grown and new pesticides have come on the market. Habitat loss and habitat degradation are rampant. Grasslands that remain are small and isolated. There are fewer hedgerows. There is less crop diversity, which leads to shorter flowering times. Rusty patched bumble bees tend to emerge earlier in the spring and remain active later in the fall, and so depend on a variety of plant species throughout the season. The emergence of the bees from hibernation and the flowering of the plants they depend on may no longer be in synch. Corn and soybean monocultures have become more dominant at the expense of the hayfields so loved by the bees. Climate change may also be playing a role. Extremes of temperature and precipitation also take a toll on the bees.

As their numbers decline, rusty patched bumble bees also become vulnerable to the damaging effects of smaller populations. A “diploid male vortex” occurs, which basically means that as the population decreases the proportion of non-viable or reproductively impaired males increases, which further decreases the population.

Do Something

There are a few things we can do:

• Grow native plants in your yard.

• Plant some early-flowering shrubs.

• Grow a garden.

• Buy plants and seeds that you know have not been treated with neonicotinoids or other insecticides.

• Make a pest of yourself and ask at the garden stores to stop using pesticides and fertilizers.

• Leave some unmowed brushy areas in your yard.

• Don’t rake up all your leaves. Hibernating bumble bee queens need winter habitat, so leave some bare ground and cozy rodent holes for nesting.

• And if you are so lucky as to have bumble bees in your yard, don’t crowd them.Mark off where they seem to be nesting in the ground and avoid that area. They are much more docile than honey bees and only sting if you bother their nest. They have smooth stingers so they do not die after stinging. The new queen will most likely not use that same area the following year.

• If you’d like to take a more active citizen-scientist role, join Bumble Bee Watch. And keep hoping that the rusty-patched recovers before it’s too late.

Joan Schnabel is a physician and a raptor educator who lives in Iowa City. Her last story for Big River was “Living with a Vulture,” November-December 2016.

"Bumble bees of the Eastern United States" poster from the Pollinator Partnership (Click on image for printable pdf)

©2017 Big River Magazine