California’s bumble bees are vanishing

In a recent survey of California’s bumble bees, only 17 species were found, making up just 68 percent of the estimated species diversity of the state. The last survey of bumble bee populations was carried out in the 1980s. The current study, conducted by researchers at UC Riverside (UCR), was a long overdue follow-up to investigate where bee populations are now.

Besides being beautiful creatures with their own lives and role in the universe, scientists remind us that bumble bees also pollinate some $3 billion worth of crops every year in the United States. The plants that are pollinated by bees include spicy peppers, delicious tomatoes and tart cranberries.    

The UCR team, led by entomologist Hollis Woodard, surveyed 17 sites throughout California comprising six different ecosystems where an abundance of bees had previously been found. The researchers tried in four additional locations in southern California but were only able to find ten individual bees at those locations.

“Although we found that relative to other sites the mountains are home to the most diverse bumble bee populations, even at those sites we also failed to find some species that used to be there,” said Woodard. 

One of the most common bees, the western bumble bee – which is also an important pollinator – was not found anywhere during the survey. “We didn’t find it even once,” said Woodard. “If it was okay, we should have seen it.”

Over half of the bees collected were one species, the yellow-faced bumble bee (Bombus vosnesenskii) making it the most commonly found species in the survey. Even still, this bee has shrunk in population size as well. 

“Even the most dominant species has lost a lot of suitable habitat since the last large-scale survey,” said Woodard. “The winner is not doing great.”

In an attempt to limit their damage to the already imperiled insects, the scientists collected just 100 bees at each site, a relatively small number for this type of survey, 

A recent court decision put four species of bumble bee on California’s state endangered species list, but none of these species was found during the survey. These bees were already on the federal endangered species list. 

“Generally, the state list directs more action toward more local measures. It’s good for them to be covered under both,” said Woodard. “I hope the state listing also encourages Californians to feel like they have a stake in helping the bees survive, because bees certainly help humans survive.”

Now, we can only hope that the listing isn’t too late to protect these bee species, which may or may not be already gone.

The study is published in the journal Ecology and Evolution.

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By Zach Fitzner, Earth.com Staff Writer