Saturday, April 10, 2010

Solitary Bees Part I

Solitary Hornfaced Bees pollinate a Callery Pear in Western North Carolina, Spring 2010
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When people think of Hymenoptera - the order of insects that contains ants, bees, and wasps, we generally think of social creatures that operate in a hive or nest environment, with various individuals living their entire lives dedicated to one single task - whether it be defending the nest, finding and delivering food, or simply reproducing over and over again. Our most well-known species within the order certainly fit the bill - honeybees, sugar ants, yellowjackets, just to name a few. These are highly specialized species with highly specialized social skills.
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Just as interesting is that there are hundreds of species of bees that contact another adult of their species only once a year - perhaps once in a lifetime - with the sole purpose of reproducing. These bees live the rest of their lives alone, and because of that we call them "solitary bees." What we've just started to learn in the last 50 years is that these bees are more durable, efficient, effective, and even more speedy pollinators than European honeybee - a species used for human agriculture for well over 2,000 years. As you may have heard, the honeybee - used to pollinate over 100 commercial crops worldwide - is in great danger, thanks to an aggressive mite called "Varroa" and a disease (perhaps a fungus) called "hive collapse disorder." For this reason, people are starting to look at our other bees, and whether they can be managed to help produce food for humans.


Carpenter Bee (a large solitary bee) pollinates a Redbud shrub in our Baltimore yard
- Spring 2010
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Let's take a look at a solitary bee that you already know - the Carpenter Bee. In mid-latitudes (most of the continental USA for example), the large, slow black buzzing bee that you may encounter in spring flower gardens (or under your deck if you are a landowner!) is not a bumblebee at all - but a Carpenter Bee. Bumblebees form small colonies holding less than 100 bees - but they are colonies nonetheless. Carpenter bees drill holes into soft, old wood, including lumber, to lay an individual egg and to provide the egg with food for after the hatch.
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Carpenter bees have naturally evolved to emerge in early spring and take advantage of spring flowers before many other pollinators have emerged from hibernation. In areas where a lot of high quality nesting habitat exists (like my neighbor's rotting, abandoned garage), Carpenter bees will intentionally nest near their relatives - while never providing for or defending their "sisters' " nests. Wikipedia states that the bees will occasionally work together, but it seems rather dubious. Carpenter bees are used in some areas to pollinate food crops with wide, open flowers.

Bumblebee - a large, social bee - on Hyssop var. Black Adder in our yard, Summer 2008.
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Note the difference between the Bumblebee and the Carpenter Bees above and below.

Carpenter Bee on Common Milkweed - Northern Maryland, 2004.
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Our modern agricultural system is so intensive that every year, hives of honeybees are moved across the United States from orchard to farm to orchard to help pollinate food crops. This costs farmers millions of dollars per year. Always interested in "efficiency farming," the USDA conducted a study in the late 1970s to confirm the accepted thought that honeybees are the world's best pollinators. They found out that humans had been wrong all along.
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In a move that could best be described as somewhere between "haphazard" and "suicidal," the USDA Research Farm in Beltsville, Maryland introduced a new, highly efficient solitary bee into the United States - the Japanese Hornfaced Bee. How could the USDA be so reckless? Well, as it turns out, one Hornfaced Bee does the work of ONE HUNDRED honeybees. The Hornfaced Bee has expanded its range throughout the Mid-Atlantic and possibly into the Great Lakes states. Logically valid concerns exist about the impact these bees could have on other (native) solitary bees, but almost 30 years later, no negative impact has been observed (except that an accidentally imported Japanese predator wasp has found the Hornfaced...as well as its American relatives). And yes, they are for sale, but please, buy genetic stock that has already been introduced to your region! A picture of two Hornfaced bees can be found at the beginning of this post.
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The Hornfaced Bee is known as Osmia cornifrons, and as it turns out, North America has a few Osmias of our own that do a pretty amazing job of pollination (though perhaps not quite at the level of the Hornfaced). I've been managing different types of "bee condos" for solitary bees for several years, and these girls have just showed up in the last two years....can't quite identify them:

A Mason Bee (of some variety) delivers food to the drilled out stump I provide for them in our Maryland yard. Last year, they used every cavity!
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In my next post on this topic (unless someone requests more pictures of our mystery bee here), I'll discuss the effects that good management of solitary bees can have on your garden and fruit trees, and some "lessons learned" on how to increase the use of your property by solitary bees.
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Thanks for stopping by, as always!

3 comments:

biobabbler said...

Ooh, the prospect of drilling one of our less beloved trees full of holes for mason bees is attractive. What size drill bit did you use?

Swamp Thing said...

I've mixed it up with 5/16, 1/4, and 3/8. Seems no rhyme or reason why they choose one or the other.

If you drill into a live tree, it's a one-year deal - around the time the bees hatch, the tree will start to close the wound itself.

Dead trees & old lumber are the way to go.

biobabbler said...

Great. Thanks very much. Snag drilling it is. =)