Digger Bees

Question: Hello,
I live in a townhouse, in Gaithersburg, MD, and my front yard is all composted soil, no grass, just plants and is about 20 feet x 15 feet including the walkway.  Later this spring I used a spade to loosen the soil and at the same time my neighbor laid down new mulch (her yard is mainly mulch with a few plantings).  All of a sudden we had dozens of digger bees.  I think the digger bees came from her mulch.  I looked at your extension website and they said not to harm the digger bees.  The digger bees chewed the roots of almost all my primroses as there was nothing blooming at that time and the primroses all died.  When I was trying to prune away the spent flowers the primroses all came away in my hands.  Per online non-chemical methods to get rid of them was sprinkling cinnamon, using peppermint oil, and finally laying down a heavy layer of mulch but none of them were of any use.  The digger bees dug holes in the soil and created a ¼ inch muddy hold on the surface.  Finally I had to resort to use of chemicals but of course by that time all my primroses were gone .  The bees didn’t stay in my neighbor’s yard and they all migrated to my yard.  They didn’t go to her neighbor on the other side which has grass and other neighbors to the left of her all have grass yards.

My questions are:
•	I thought that the digger bees only dig when there is grass so why did they come to my yard?
•	How do I prevent the digger bees from appearing next year?
•	I’m really mad at the digger bees for destroying my primroses when I have propagated for years and I don’t want them back.  How do I prevent them coming back?
•	Why didn’t the digger bees go to her neighbors on the other side which all have grass yards?

Attached are photos of the exteriors of my house and my neighbors’ house to give you any idea of the space we are dealing with.  The digger bees are now gone but I don’t relish their appearance next year.  Any ideas for what I can do to prevent them coming back.

Thank you!
Zeba

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied June 22, 2023, 11:03 AM EDT
response: Hello Zeba,  Ground-nesting bees, which comprise the vast majority of our native solitary bee species, were not responsible for the demise of the Primrose, nor did they arrive via the mulch since they cannot use mulch for nesting. It would be hard to diagnose the cause of damage for the plants after they'd already died and without pictures of their symptoms, but root or crown rot, drought stress, vole feeding damage, or a chewing insect pest (perhaps beetle grubs) are more likely. The timing of the two occurrences is either coincidence or otherwise unrelated to the bees themselves, even if something was wrong with the mulch or soil in that area.  Home remedies are not reliable for insect repellency or treatment and are discouraged because they may cause other environmental harm. The bees were likely taking advantage of loosened soil for nesting since they have a harder time digging burrows in very compacted soil or in soil covered with a barrier like mulch. (Mulch would help prevent the formation of a burrow, but if the burrow was already there and then covered with mulch, the bees will reopen the nest entrance if they can.) If the bees appeared suddenly, it's possible a group of juveniles was already present in the soil from the year prior and had just matured and emerged, flying around to find mates before starting their own burrows. Male bees die soon after mating as they do not participate in burrow construction or providing for the young.  It is correct that solitary bees are highly valued pollinators and should not be eradicated if at all possible since they have little suitable habitat left in natural areas. Once females have started forming burrows to provision with pollen for their young, it may be hard to get them to leave, and any disturbance of their activities by using a repellent (not that any would work well in this case) or insecticide spray would doom the baby bees in burrows to starvation since they cannot acquire their own food. A soil-applied insecticide might also risk harming other insects if absorbed by nearby plant roots. The period of activity for adult ground-nesting bees is relatively brief (a few weeks, typically) since most species rely on the blooms of a very particular group of plants that won't be blooming all summer, so once they are finished stocking the burrows with food for the larvae the adults leave or die off. Since they do not sting people to defend their nests, and since these burrows can actually benefit soil and root health because of its soil aeration, management of ground-nesting bees is not needed or recommended if it's possible to live with them.  If the bees didn't stay in the neighbor's or nearby yards, it could have been because the soil there was less suitable for nesting (maybe too poorly-drained or too compacted from foot traffic) or they may have applied insecticide (grub control, anything) or some other pesticide to the yard. Even products not intended for insect control (like weed killer or a fungicide) can have harmful impacts on bees. There are hundreds of species of bees found in Maryland (plus solitary wasps that nest in the ground too, but don't sting people) and their nesting habitat preferences will differ, so without knowing which type these were, it's hard to say what exact conditions they prefer. Therefore, it's hard to say what conditions will discourage them from coming back, but as we've mentioned so far, compacted soil (which is not good for plant roots) and soil covered in a barrier like mulch that's hard for them to dig though is not likely to appeal to them. A living groundcover is also not generally what they seek to nest under, as most prefer exposed soil.  If you see more of the bees (granted, this might not occur until next year when the new generation of adults emerge), sharing photos with us of the bees themselves and the style of burrow (with a soil pile next to it, for example) is helpful for trying to identify them in order to know what conditions may be attracting them. You can try again with the primrose if you prefer, though generally they struggle in Maryland weather conditions (heat, mainly) and are not common components of area gardens.  Miri

responder: The Question Asker Replied June 23, 2023, 1:40 PM EDT
response: Dear Miri, Thank you for the detailed information you provided!  I should have taken photos of the bees and their burrows but my mind was so focused on getting rid of them that I didn’t think of it.  The reason I think that the bees destroyed my primroses is that I saw them going in at the roots of the primroses and when I went to prune the spent primroses the primroses just came up in my hands with the little roots they had left..  I have these primroses for at least 10 years and this has never happened before.  Also there was nothing blooming in my yard when the bees came, the daffodils, the hyacinths and primroses had already made their appearance and gone so there was no pollen for these bees to collect and to my thinking that’s why they went for the primroses roots.  There was a lavender beginning to bloom but I didn’t see these bees going in at the roots as much, because I think the lavender roots are more woodsy and primrose roots are more succulent.  But that’s my nonscientific brain trying to make sense of why the bees were so keen on the primroses.    Next time I will forgo all the dumb home remedies and chemicals and email you, with photos, immediately.      Thank you very much for such a detailed email. Zeba

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied June 23, 2023, 2:26 PM EDT
response: Hi Zeba,  You're welcome. That's quite alright, it can be hard to get good photos of those busy little bees anyway, but we'll see what happens with them next year when the new generation appears. Bees won't feed on plant roots (they can't use them as source of food) and while digging into the root zone might disturb a plant a little, we doubt this was what happened or would have been drastic enough by itself to kill a plant, especially given that this affected all of the plants equally severely. A soil-borne infection of the roots or some other explanation unrelated to the bees is more likely. Even if a nectar or pollen source wasn't available in your garden beds at the time, they can fly enough distance to find what they need (and sometimes they're actually collecting tree pollen beyond our notice).  Miri

responder: The Question Asker Replied June 25, 2023, 3:00 PM EDT
response: Hi Miri, The bees only effected my primroses (to my observation) and no other plants and now there are only about four primroses left.  Though there were burrows all over my non-grass yard I only saw them going into the root base of the primroses.  Literally there were hundreds of bees in my little yard.  My yard was not mulched at the time and even when I mulched it they kept going into the roots of the primroses.  They didn’t bother the clematis or other plants that had just started to emerge.  Why the heck did they appear when there were no plants for them to collect the nectar?  There are lots of trees where I live so maybe they were collecting tree pollen.  Is it possible they were another species of bee or wasp?  They didn’t bother or bite me just buzzed around when I was pruning my primroses.  I also read that these bees maybe eating Japanese Beetle’s grubs which I have had in the past and had to pull out my knockout rose bushes because the Japanese Beetles wouldn’t leave them alone for four years in a row.  I promise I will not use chemicals anymore on my front yard – it was just the exasperation with the digger bees that drove me to it.    Thanks so much for invaluable information.  I have learned so much more about digger bees and I want to thank you for taking the time to explain all their habits to me. Zeba

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied June 26, 2023, 4:49 PM EDT
response: Without images of the bees in question we can't make any more guesses about what they were doing in such close proximity to the primrose plants, except to say that it's highly unlikely they intentionally damaged any roots. Yes, it's possible they were a ground-nesting wasp, though in this situation they would not be one of the species likely to bother people (like Yellowjackets) as they are nesting singly. They would not be Cicada Killer Wasps, as they don't emerge that early (and they're unmistakably large), and probably were not grub-hunting wasps as they tend to appear later in the season than these did as well.  Ground-nesting bees and wasps can appear without nectar plants in the immediate vicinity because they will fly a certain distance (maybe halfway across the neighborhood, it really depends on the bee) to forage for the flowers that suit their needs. If they are wasps, the adults will visit flowers for nectar but the rest of the time they are looking for insect prey for their nest, so the presence of flowers nearby isn't a deal-breaker for them. Some bees are very particular about what plant nectar or pollen they can use. As we mentioned before, it might be that your yard had less chemical exposure and just the right type of soil for their nesting needs that allowed them to nest in your yard but not the nearby yards.  You're welcome, and feel free to send us pictures of the bees/wasps if they appear again in the future.  Miri

responder: The Question Asker Replied June 28, 2023, 2:05 PM EDT
response: Dear Miri, Thank you for all the help and information you provided. Next year I will be ready with my camera to capture these insects and photos of their nests. Take care, Zeba

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied June 28, 2023, 4:28 PM EDT
response: You're welcome!

responder: The Question Asker Replied May 02, 2024, 6:06 PM EDT
response: Hello Miri, It’s me again with my bee problems!  I had tried sending a video of the bees but apparently the file is too big to send…I will keep trying.  Though you can’t see the bees but you will see how fast and furious they are.  By furious I mean their speed not how aggressive they are and I have not been stung by them.  However I was able to trap a couple of them in a netting and then sprayed them with insecticide until they died and would like to mail you those so you can examine them further.    Could you please send me your postal address so I can mail them to you?    Hopefully you will tell me how to get rid of them!  They are only in my front yard, not my neighbors.  I have no lawn just mulch and plants and they are now congregating under the new hydrangea I just planted.  They are so many of these bees.    Thank you so much! Zeba

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied May 02, 2024, 6:18 PM EDT
response: Hello Zeba,  The Ask Extension platform only accepts image files, though you could send us a link to a video you took that you put online elsewhere. As you noted, though, we probably won't be able to determine much identification-wise from a video since they will be moving too fast. If you can film a bee landing and entering its nest, that might be more useful for ID since it won't be moving as much.  We do not generally accept samples, and would not want to receive insects that were sprayed with insecticide (which also probably should not be sent through the mail). If you would like to capture a couple live bees intact, you can put them in the freezer to euthanize them safely and then take photos of them that way, where they are clean, dry, and well-lit, all of which are important for identification. Images need to be in focus (the bees in the bag are not, unfortunately) and posing the bees next to a ruler would be very helpful. (It can also give the camera something detailed to focus on.)  With a new set of clearer images and unaltered bees, we can see if our entomologist can recognize them. It doesn't change much about our prior recommendations to discourage their nesting in that location, however, nor does it change the fact that they should not bother or sting anyone while they are active. We encourage gardeners to let native solitary bees nest undisturbed if at all possible, especially since they are not active for the whole season.  Miri

responder: The Question Asker Replied May 05, 2024, 4:46 PM EDT
response: Dear Miri, Thank you for all the suggestions below.    The bees are moving too fast, almost swarming, so it’s hard to film them much less catch them digging into the roots of the plants.  You don’t see them land on a plant or burrow into the yard they are that fast.  You don’t actually see them, just hear them buzzing and little dots zipping around.  You don’t get to see them.  That’s why I had to trap them in a netting.  Maybe I will try to trap some more bees and freeze them then take some photos of them next to a ruler for measurement.  I had a neighbor try to film, or take a photo of them, and he also was unsuccessful because that’s how fast they are.  They don’t come out during rain, or when it gets cloudy or dark just when it is nice and sunny.    You are right that a bug sprayed with insecticide shouldn’t be sent through the mail.  My insecticide soap was organic and hopefully not poisonous but I thank you for pointing this out.    What I don’t understand is why are they only in my little front yard and not in any of the neighbors?  I don’t want to harm the bees if they are beneficial and not harming anything but they seem to dig where I have a clematis and where I just planted a hydrangea.  Last year they chewed away at the roots most of my primroses and the those chewed away primroses did not emerge this year.  I don’t mind bees at all but I don’t want them eating away at my plants hence the use of my organic insecticide soap spray.    Thank you for your invaluable guidance and advice.  Zeba

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied May 06, 2024, 12:29 PM EDT
response: Hi Zeba,  As we mentioned last year, the bees are not responsible for killing the primroses, and they are only taking advantage of the loosened soil (like around the clematis and hydrangea you mention) to dig their nesting burrows more easily. They do not harm plants, and if the primrose died out, another factor was the reason. (Possibly soil drainage, as several types of primrose either require damp conditions or require good drainage, depending on the species. Primroses are not commonly grown long-term in Maryland gardens because they seem to struggle in our conditions, especially our heat and humidity during summer.)  The photo you sent this time is more helpful, thank you, but unfortunately the file size is too small for us to see well because we can't enlarge it. Do you have another, larger version of this photo you can send instead?  We can try to ID them to group from the photo once we can see enough detail, but overall, no ground-nesting bee of this type will bother people, and their frantic activity will soon cease. Like we said previously, we think they like your yard conditions because you said you don't have lawn, and perhaps the neighbors are applying pesticides to their lawns and you are not, making conditions more hospitable for them to thrive and provide their valued pollination services.  Miri

responder: The Question Asker Replied May 06, 2024, 1:47 PM EDT
response: Hi Miri, I have had the same primroses for over 20 years, that I divided and replanted every couple or three years, and I have never had a problem with them and they always come up healthy and cheerful.  Last year all the bees were going at the primroses roots and when I tried to pull up on the primroses it would just come up.  The primroses were healthy before the bees.  But we can agree to disagree on the primroses J.    I finally figured out how to zoom in the camera on my iphone!  So have a better photo.  If you need more photos please let me know. Thank you! Zeba

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied May 06, 2024, 3:11 PM EDT
response: Bees won't be chewing through roots to excavate a burrow, but in either case, whatever damage was done with a root rot or other factor can't be undone, unfortunately. Thank you for the new photo. I should have specified that our entomologist will need to see the top of the bee as well, where the wing veins and other features are visible. Your image is nicely zoomed-in, but the marking scale on the ruler is cut off, so we can't tell what measurements we're looking at. Can you also share a close-up photo of the nest holes? (One picture showing several nest hole entrances, if possible.) That can help her narrow-down which kind of ground-nesting bee may be responsible (since some have soil mounds outside of their burrows and others do not). Hundreds of bee species occur in Maryland and many superficially look alike, which is why we need as many identifying features as possible to be visible in photos. A larger image (over 1 MB in file size) of the one you sent previously should suffice as well, since it looks like one bee is sideways and one is facing downwards, which will show us two different viewing angles, which is helpful.  Miri

responder: The Question Asker Replied May 06, 2024, 3:45 PM EDT
response: Dear Miri, Let’s not talk about my primroses because I know what I saw and what they did.  In my opinion, it was not primrose root rot the plants the bees ate away at didn’t survive and those that they didn’t eat  away at survived fine even when inches from each other.  I know the bees came from the bags of mulch that my neighbor was putting down – there were bees in her yard and then they came to mine.    I will be sending a bunch of bee photos to you in separate emails as my outgoing email can’t handle an excessive amount of data.    There are no burrows or soil mounds that I can see as I already have shredded mulch in the yard where the bees are going in.  They do NOT burrow in the ground, they like to burrow underneath a blooming plant.  Last year I think I did see burrows as I was using cinnamon, and Dr. Bronner peppermint soap, to discourage them.    There are no bees in the yard today as it is cloudy.  They only come out when sunny.    Thanks so much! Zeba

responder: The Question Asker Replied May 06, 2024, 3:51 PM EDT

responder: Answered by University of Maryland Extension faculty. For more information on a variety of yard and garden topics, visit the HGIC program web page and blog, Maryland Grows. Replied May 07, 2024, 1:54 PM EDT
response: Hello Zeba, This is Madeline Potter, an entomologist with the University of Maryland Extension. Based on your photos this insect appears to be some kind of mining bee, likely the bee family Andrenidae. We have over 100 species of bees from this family in Maryland. As Miri said last June, these wild bees are very important pollinators in our ecosystems and unfortunately many of their populations are suffering due to habitat loss and pesticide use. Since you are seeing these bees each spring, it appears you have the right conditions in your greenspace for their habitat preferences. This is great news in regards to your yard providing habitat for beneficial insects. I can only imagine how frustrating it is to lose many of your primroses. These particular bees are likely nesting near your primroses, like you described, because they pollinator these flowers and they prefer to be near their needed pollen and nectar resources. It would not be advantageous for these bees to harm the flowers they rely on. Biologically these bees do not chew plants or plant roots so you can rest assured that they are not harming your plants in this way. If you want to send us photos of your primroses we may be able to provide further guidance as there are many other living and nonliving things that could be affecting your plants. If you wish to deter the bees from your yard the best management recommendations are to increase vegetative cover as these bees tend to prefer bare, well drained, sandy soil. This could mean increasing the amount of plants in your space to cover bare patches.  To reiterate what Miri said, these bees are only active for a couple weeks and if they can be tolerated, they provide beneficial services to your yard and our environment. Ultimately it is your choice whether you take action against the bees or not. Miri and I have provided our recommendations. We do not recommend using any homemade remedies such as cinnamon and/or peppermint soap/oil. It is important to note that since climate varies each year, even plants that we have had for years can have changes in their health and growth. Feel free to send any further photos, particularly of any plants that are not doing well, otherwise we have provided all the recommendations and information that we can at this point.  If you would like to read more about mining bees, please see our mining bee webpage: https://extension.umd.edu/resource/mining-bees-lawns/.  Thank you for reaching out to the University of Maryland Extension.

responder: The Question Asker Replied May 09, 2024, 2:19 PM EDT
response: Hello Madeline, Last year, 2023, was the first year the bees appeared and they came from the bagged nugget mulch that my neighbor laid down as her yard is plastic sheeting with mulch on top with no grass.   They migrated to my yard which is Montgomery County Leaf Gro, soil conditioner, with a thin layer of shredded mulch on top.  Maybe since being trapped in the plastic bags of mulch that my neighbor used they needed some nutrition and chewed at the primroses roots as it was the only flowering plant growing at that time.   This year they didn’t chew the roots of the few remaining primroses.    This year, 2024, these bees were near my clematis and my newly planted hydrangeas roots but the salvia or the milkweed is not out yet so I wonder how the bees are nourishing themselves?  As I don’t think either the clematis or the hydrangeas is purely bred.  But they do go under the clematis and hydrangeas.  The photos of the bees I sent were from earlier this year and I noticed they have got bigger since I sent Miri, and you, the photos.    I am very concerned with our environment and want to preserve our habitat for them.  I don’t usually use pesticides or insecticides but I was really angry with the bees last year when they chewed away at my primroses.  As I mentioned to Miri, they ate away at the roots, as the primroses would easily come away in my hands after the bees were at them.  The primroses were next to each other and most didn’t make while a few did.  Last year I did use cinnamon, and Dr. Bronner’s peppermint oil soap mixed with water, to try to deter them again being angry at the bees for eating away at the roots of my many primroses.    If these bees are important pollinators I promise to stay away from insecticides and pesticides provided they don’t harm my plants.  I will add a caryopteris blue beard spirea as it attracted a lot of bees to a friend’s landscape.  As per your suggestion, I will add more vegetative cover in addition to the two hydrangeas I have also planted seeds for nasturtiums and will also add some more milkweed as well.  My intention is to populate my yard with living green plants that also do good for the environment.    Thank you, to both you and Miri, for your guidance and sound advice with the mining bees.  I appreciated both of your replies to all my emails!! Take care, Zeba