Sunday, May 26, 2013

Mining Bees

One of our neighbors has a stretch of lawn where I noticed a lot of mining activity last year and again this year around the same time (early May). I could tell they were ground bees of some sort since you could see them flying and hovering around the mounds of dirt. We pretty quickly determined they were harmless when the dogs walked through an area we thought was free of them, but turned out to have some holes. The bees didn't try to sting the dogs (unlike those sweat bees that sting the heck out of you if you accidentally mow over their nest). It seemed to me the area they covered this year had doubled over last year and they were definitely much more densely packed than last year. The entire area covered maybe fifteen by thirty feet.

Unlike honey bees, mining bees do not have nests containing many bees, but live in individual burrows. I guess you can still call it a colony even though the bees live in single family homes instead of condos. They must burrow fairly deep because the soil around their holes is not topsoil, but the red clay from deeper down in the ground. They also must have some means of gluing dirt particles together into larger packages because the dirt around their nests was not single grains as you see around ant holes, but granular balls of dirt.

Mining bees range in size from about the size of honey bees to much smaller. The larger bees are furry and usually darker in color than honey bees. Some are brightly striped, while others are a shiny metallic green. Here, you can see one emerging from the entrance which is about a quarter inch in diameter.

Notice how many different "looks" there are to the bees in these photos. I'm not sure if some are male and others female, or whether several species were nesting in the same area. They also varied greatly in size. One odd thing while I was photographing them - when the sun was out, you would see them flying or hovering around the nest. When the sun went behind the clouds, you couldn't hardly find one.

Their tunnels consist of a vertical shaft with side chambers where the females deposits an egg on a food mass consisting of nectar and pollen collected from flowers. Some of these bees are very specific pollinators and if the plant they rely on disappears, so do the bees. The larva hatches, consumes the food mass and goes into a pupal stage, finally hatching into an adult bee early the following year. The bees overwinter in the ground, emerging the following spring to mate and start the entire cycle all over again.

One question that comes to my mind is, How in the world do they relocate their nest once they fly off? With hundreds of nest, all looking alike, they must have a unique "gps" system in order to get back home. 

Some females can be distinguished from males by a velvety patch of hair on the forehead at the base of the antennae.

Perhaps one of these two bees, which appeared to be fighting, went into the wrong nest. All activity ends after about three or four weeks and they disappear for another year. There are something like 1300 different species of mining bees altogether. They are beneficial as pollinators and as aerators of the ground and not being prone to stinging, I would hope there would be little incentive to try to eliminate them if they happen to nest in your area.

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