Tuesday, July 10, 2012

Insect collection update: the year of the Bombus

Indiscriminate cuckoo bumble bee (Bombus insularis)
Last year I started an insect collection in order to document (and learn) all the insects visiting our garden. This project has been so much fun and such a rewarding endeavor.  I am constantly amazed by the abundance and diversity of insects using our garden, and I am always fascinated by the ecological interactions going on in our little yard.

Last year I was obsessed with bee mimics- a variety of species, genera, and families that mimic bees and wasps.  The ecology of these animals, and deception they employ, are really fascinating.  This year, I am fascinated by bumble bees (Bombus species)- the gentle giants of Hymenoptera. 

There has been a lot written about many pollinators, and even bumble bees in particular.  Many species of bumble bees have declined for a variety of reasons- and many of them are the usual suspects- habitat loss, climate change, pesticides, etc… but another thing that intrigues me about bumblebees and their conservation is their nesting requirements.  This relates directly to conventional landscaping.  Bumblebees nest in the ground in underground burrows, so, more than anything, they need access to the ground: bare dirt they can burrow in to. This behavior puts them at odds with lawns, which cover most landscapes.

Bumble bees are not alone in being affected by lawns, indeed most of our native bees (over 75%) nest in the ground. However some species nest above ground in hollow cavities- holes formed by woodpecker drilling, from other insects boring into trees and even in hollow stems of plants like milkweed (Asclepias speciosa). These are the cavity nesting bees, like mason bees (Osmia species), that nest in bee boxes. For our other native bees (like bumble bees), bare ground is what they need. But unlike most of our native bees, which are solitary nesters, bumble bees are social and live in colonies.

The original mason bee box
Everyone likes bumble bees, and along with ladybird beetles and butterflies they are probably the best known insects in the garden (and most liked). But I realized I knew very little about them, despite that they are large, colorful, and easy to observe. Surprisingly, bumble bees can be hard to identify, and this speaks to their social nature and community structure. Within a species, males, workers and queens are often very differently colored, and are even present at different times of the year. Combined with the fact that there are local variations and over 20 species in west-central Montana, even though they are large and easily observed (and captured) they can be tough to identify.

So far I have collected and identified 12 species in our garden. Most of these are pretty common species, perhaps with the exception of the western bumble bee (B. occidentalis). Though locally common, the western bumble bee is in decline throughout its range and has even been locally extirpated, making it a species of concern throughout its range now. Historically they ranged from the Pacific coast east into Rockies and south to New Mexico.

Although several guides and resources are available, there is no one guide that is perfect for species found here in Montana.  As a result, in order to identify bumble bee species  I have been using a combination of guides including this key from Discover Life,  a guide to Bumble Bees of the Western United States by the US Forest Service, a guide to bumble bees in North America by bumblebee.org  and other online resources, like bugguide.net.  Even with all these resources I still have some questions, and I still have a couple of specimens I have yet to satisfactorily identify.  This is not to scare people off- it is a lot of fun learning about them and identifying them and many are actually quite easy to identify.  One of my best references has become my own insect collection.

The interesting thing is all the diversity that is out there, and all the interesting behaviors and ecology.  And all this can be found in your own backyard, provided you remove some lawn, plant some native plants, and take a look at what happens. So, last year, for me it was all about the mimics, and this year, bumble bees have my interest. Fortunately, there are hundreds of more species in my garden to keep my attention for years to come.


  1. I just want to be clear that the Xerces Society did not publish Bumble Bees of Western United States. That guide was published by the USDA Forest Service with funding from others. It was written by Jonathan Koch, James Stange and Paul Williams. Please change the attribution on this page. We do however have a bunch of good information on bumble bees at www.xerces.org/bumblebees. And we are VERY interested in any sightings of the western bumble bee as its status is in question and population trends are alarming.
    Rich Hatfield
    The Xerces Society
    bumblebees (at) xerces.org