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Why do I see mining bees in September?

In the past week I received two nearly identical questions about mining bees. Both writers wanted to know why they had mining bees in September while everyone says that mining bees come in the spring. Excellent questions.

DJ wrote:

All I read about these bees indicates they are usually around in early spring, but mine are here now and intermittently throughout the summer. Is that normal? I have a lot of flowering plants like catmint which all of my bee friends seem to love and I’m wondering if they are just visiting me longer because of all the pollen and goodies. I feel bad they have landed where they did because it is near where we walk for our hose and I am always walking on their little mounds of sand and soil.

Shortly afterward, Keith wrote:

I was never aware of mining bees until this past week when literally thousands of them were hovering over a bare area on the property. My question is most comments seem to refer to spring, and a relatively short span of activity. But this is early September! Does timing of activity vary that much with species, or is something else going on? I hadn’t seen the myriad of individual, small holes in the ground until I got down on my knees to look at/try to identify the fliers. From a standing position, it was impossible to see what they were because of their small size and rapid movement.

I love that these two people have enough confidence in their observations to question what they’ve heard about mining bees. And of course, they are both right. The species of bees that are active changes throughout the year, but some bees will be around as long as flowers are blooming.

Are they native, wild, or feral?

Any discussion about bees has to begin with the words we use to describe them. There doesn’t seem to be a standard, but you can categorize bees by how they got here.

For example, most of the bees here in North America are native to the continent and were here when the colonists arrived. But others have been introduced on purpose and subsequently escaped into the environment. These escapees became established, much like introduced weeds. Examples are wild populations of the European honey bee and the alfalfa leafcutting bee. Still other bees were introduced accidentally and were never managed, such as the European wool carder bee. All three of these categories can be referred to as “wild.” The opposite of wild are those that are currently managed, such as most European honey bees.

Common names are confusing

When it comes to identifying bees, I again think it’s the names that confuse people. For example, many people use the term “mason” bee to refer to bees in the genus Osmia, but in a larger sense, mason bees are any bees that collect building materials from their environment. So that makes leafcutting bees and wool carder bees masons as well.

Likewise, the terms “mining bee,” “digger bee,” and “sweat bee” each comprise hundreds and sometimes thousands of different species. So when one person describes what he considers a mining bee, it probably isn’t the same species that someone else is calling a mining bee. These names are based on broad descriptions of behavior more than anything, so they are not names of specific species.

Sometimes there is a bit of correlation that develops over time. For example, the term “mining bee” is often used to describe bees in the genus Andrena, while “digger bee” is used for the genus Anthophora, but both are large groups of bees that dig small holes in the ground. The genus Andrena alone comprises 1300 species.

What people need to realize is that Earth is home to roughly 20,000 named species of bee and probably another 10,000 to 20,000 unnamed ones. So when you use a label like “digger bee” you have to understand that the word encompasses a wide range of bees and bee behavior.

Mining bee are not limited to spring

Going back to the original questions, both DJ and Keith mention hearing that mining bees are around in the spring, but their bees are out in September and intermittently in the summer. All I can say is they are very observant.

In truth, different species of bees become active at different times of the year. A species can become active in late winter, early spring, mid spring, late spring, early summer, mid summer, late summer, early fall and so on. Each species is different and each one has a very specific time when it becomes active.

Unlike honey bees which do not hibernate, most bees spend the majority of their lives in the nest either as a larva or a pupa. The time spent in the nest varies with species, but as a rule of thumb, you can imagine bees spending about 10 months in the nest and two months as active adults. When we say bees “become active” we mean the adults emerge, mate, lay eggs, and gather provisions for their young. Once this work is done, the adults die and the next generation is on hold for 10 months until next year.

Species come and go

So when DJ says her bees are active intermittently, what she is seeing is different species coming into their active period at different times of year. Of course, nature is complex and nothing is easy to pigeonhole. For example, there are species of bees that have two life cycles in one year. Other bees—like some of the bumbles—appear to have longer active periods because they live in colonies which persist for months. And the real outliers, colonies of honey bees, do not have a dormant or hibernating stage at all. But for most species, the life cycle is less than 2 months of activity followed by 10 months holed up in the nest in an immature form.

Bees become active when the flowers they evolved with come into bloom. So the mix of bees changes with the mix of flowers. That means if you were to inventory all the bees in your backyard on May 1 you would have a very different list than you would on a different date, let’s say August 1. Honey bees would be on both lists, and maybe some of the bumble bees, but the others would be different. Even if you were to compare inventories one month apart, say May 1 and June 1, you would see a big difference. Just as the flowers change, so do the bees.

Spring brings lots of variety

I agree that people say mining bees are active in the spring and then disappear, and I’m sure I’ve said that too. The reason, I think, is that many more species are active in the spring than in the fall, just as many more flowers bloom in the spring. But that doesn’t mean there are no mining bees the rest of the year. Bees are all over the place, and many of them find flowers the rest of us barely notice.

The same applies to mason bees. When people say masons are only active in the spring, they are talking about specific species, maybe Osmia lignaria or Osmia aglaia. But there are also very early masons, late spring masons, summer masons, and so on.

DJ mentions the number of flowering plants she has and wonders if that is a cause for all the bees. Absolutely! Remember bees and flowers are dependent on each other, and where you find a lot of one, you will find a lot of the other. The more flowering plants you have, the more bees you will have, and not just in numbers but also in variety. That is why planting flowers is so important to bee conservation: more varieties of flower can support more species of bees.

Walking on mounds

DJ’s last question is about walking on the mounds, technically known as tumuli. If you go out of your way to destroy all the tumuli all of the time, you will do damage to your bee population. On the other hand, If you accidentally step on a few now and then, the bees will quickly repair the damage. Like many things in nature, it’s all a matter of degree. I recommend you use your yard normally and not worry about the mounds. I’ve seen soil-nesting bees in playgrounds, ball parks, picnic areas, backyards, and parking lots. They survive just fine as long as we don’t go out of our way to destroy them.

Keith mentions the holes in his yard are very tiny, while others claim they are quite large. But once again, the size of the hole is species-dependent. Of the 20,000+ species of bee in the world, fully 70% live in holes in the ground. That means there is an enormous variation in size, density, depth, seasonality, and soil types involved. The world of bees is anything but simple.

I don’t know if I clarified anything or not, but I love hearing from people who care. Most people ask how to kill them, so it’s a pleasure to hear from the others.

Rusty
Honey Bee Suite

A lasioglossum bee in September
Many ground-dwelling bees are active in fall. This tiny Lasioglossum female, commonly known as a sweat bee, is foraging on an Alyssum flower. © Rusty Burlew.

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Comments

DJ Baker
Reply

Thank you for this very clear and detailed answer to our questions. It has explained quite a bit. I have been careful not to trample the mounds as much as I can. They are everywhere, so it is sort of like playing “the floor is lava” but I find it amusing. I have been watching these little workers more closely since they arrived and the yellow pollen filled visitors are quite mesmerizing. Happy to have them around as long as they are here and hope to see them every year!

Thank you again. Great article.

Myrna Warren
Reply

We seem to have a bumper crop of yellowjackets attacking our honey bee hives this year. I learned from another beekeeper a non-chemical way to address this problem. Get some tuna-flavored cat food and put a couple of spoons full in a flat dish with a few drops of dish detergent and about an inch of water. Set it near the hives. The yellowjackets will be attracted to it and drown but the honey bees will not go to it.

Mike Forster
Reply

By the way, do any of these ground dwelling bees (other than bumbles) have a stinger?
I have assured worried mothers that their children are safe but I have nagging doubts too.

Rusty
Reply

Mike,

With very few exceptions, all female bees can sting. Most use their stinger for self-defense from predators. That said, most native species are not aggressive and most are so small their stingers can’t penetrate human skin. However, there are those that can pack a wallop if you were to endanger them. The males, of course, cannot sting.

Glen Buschmann
Reply

Thank you Rusty –

As I become somewhat better at recognizing all these different bees, my awe for their diversity only increases. The more I seem to recognize them the less I feel I know about them.

Thanks, GB

Li
Reply

Awesome! Thank you so much!

Beatriz Moisset
Reply

Wow! You did a great job, covering so much ground and explaining the intricacies of common names and varieties of bees.

Here is a list of non-native bees for those who are interested:
http://bugguide.net/node/view/8267#body

I envy those who have abundant bee nests in their properties.

Mike, I read about a school that discovered such aggregation of bee nests in their school yard and adopted the bees with great enthusiasm. I haven’t heard about any unhappy events. I wish I could find the link.

I discovered one aggregation next to a parking lot of a busy park. This was seven years ago and last I heard, they are going strong, more than forty nests, this year. https://www.facebook.com/beatriz.moisset/videos/4417380311997/

Rusty
Reply

Beatriz,

Thank you. I too am jealous of those who have aggregations of bees. But I do have a link to the “tickle bee” video in the Portland school yard. I frequently send it to people who are afraid of bees.

Alex T. Montes
Reply

I started 2 hives 1 month ago. One hive is doing well with a lot of activity and reproduction while the other is basically at a stand still. They are side by side yet the difference is notable.The queen in the lackluster hive seems to be ok and active yet no growth and very docile while the other hive is very aggressive and has started producing cells in a new frame. Any idea why and is there anything that can be done?

Thank you for any help you can provide. Thank you, Alex

Rusty
Reply

Alex,

I suspect you are seeing just genetic differences. You can always requeen.

Kay Baxter
Reply

The miner bees are in the ‘flower’ garden. Many many, many of them, and I feel guilty when I weed. All those homes I am destroying!! However, my garden is failing rather badly, embarrassingly so this year, (as in dead!) and I am wondering if the bees are playing any part in that. Root destruction? I certainly do not wish to do them harm, but I would like to dig out the bed and refurbish it with richer soil (that won’t be hard!!), and new plants. As I seem to have miner bees all year round it is not as if I can wait 12 weeks and they will be gone … Any suggestions gratefully received.

Kay (Baxter)

Rusty
Reply

Kay,

Tunneling bees do not hurt your plants, in fact the tunnels aerate the soil, which is a good thing. Bees are totally uninterested in roots, but they are part of a healthy ecosystem. Something else is bothering your garden. If you dig out the garden, you will kill the bees you dig out. There’s not anything you can do for them because moving them generally doesn’t work.

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