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Western bumble bee recovery?

August 3, 2014

There have been several tweets lately reporting Bombus occidentalis sightings. This is exciting because this once abundant bee has been absent from much of its range  for the past 10 plus years. For example, when I surveyed the Bumble Bees of San Francisco in 2003 & 2004, I found none, yet this bee was one of the most common San Francisco bees historically.

Although we don’t have a smoking gun, California’s leading Bumble Bee expert, Robbin Thorp, has long suspected a fungal pathogen, Nosema bombini. This invasive pathogen was likely introduced to North American bees by the commercial bumble bee industry when they shipped bees from the US to Europe then back again. If B. occidentalis recovers, it will be fascinating to learn if it has evolved resistance or if something else is happening.

It is too early to call this a recovery, but this is positive news for sure. There is a crowd-funded citizen science campaign starting up, which is really neat. There is also a citizen science reporting site called These citizen science efforts will be really important to document the recovery if it indeed happens, and I encourage you to join in. I’m really rooting for this bee, and hope that someday I can see it in California again!

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