underground bees in flower beds

Asked May 22, 2013, 8:39 AM EDT

My front flower bed has bees coming up from numerous holes. Some holes are flat, flush with the ground, and others are mounds almost like an ant hole. The bees have come back for a few years and are active during the height of the day. (time now is 8:30 a.m. and they are starting to come out to swarm). It is hard to determine what exactly they look like because they swarm in groups and I don't want to approach them, but they appear mostly black, some yellow and small. Their location is not good as it's the front sidewalk to the house, so I've roped the area off. I've sprinkled Sevin over the area, but to no avail. They've returned for a number of years . . . lay dormat for months at a time, and when they come up - usually May - they swarm a number of weeks then disappear. Help! Is there something I can treat to kill them, are they a type a beekeeper would be interested in, or does a professional need contacted to get rid of them? Thank you.

Lancaster County Pennsylvania master gardener program bees ground nesting bees

3 Responses

It's difficult to identify the type of bee from your description but it's possible you are describing "digger" bees. You may find the following information helpful in confirming the bee based on this description and images.

Digger bees are not dangerous as this article describes. If you are still uncomfortable and definitely want to eliminate your concerns then it might be best to contact a pest control firm in your area.

Digger Bees in the Landscape

There are several kinds of small hairy or metallic bees that dig into the soil to nest, hence one common name, digger bees. This is a diverse group that comes from different families and the term digger bee can include the andrenid bees, halictid bees, and colletid bees such as the plasterer and yellow-faced bees. These are solitary bees and native pollinators that are active early in the season. Each female digs a cylindrical underground tunnel as a nest where she reproduces (as opposed to social bees such as honey bees where only the queen reproduces and maintains a colony with the help of sterile workers). The subterranean nest is provisioned with a mixture of nectar and pollen collected from nearby flowering plants. This "bee-bread" is food for the bee's offspring (larvae) that develop in the underground chamber and emerge as adults the following year. Digger bees are 1/4 to 1/2 inch long and variable in color (mostly shiny metallic or dark, but some with markings of white, yellow or reddish brown). There is one generation of digger bees per summer and once the adults finish perpetuating the species by laying eggs of the next generation there will be no activity till the following spring. Digger bee nests are commonly located in areas of the landscape where the grass is sparse, either from too much shade, previous drought conditions or other stress. It is tempting to blame the bees for causing the turfgrass to be thin but it is the opposite; the bees are in the yard because the grass was already thin. The entrances to the tunnels (mounds of soil) are disruptive and annoying to the homeowner but are not usually damaging to otherwise healthy turf. The threat of being stung by digger bees is highly overrated. The bees are docile and not likely to sting unless handled or threatened. There is no nest guarding behavior or attack behavior like there is with social insects such as honey bees and yellowjacket wasps. Control is usually not necessary unless the bees are nesting close to human activity. Digger bees are important pollinators of several native plants and spring crops. Coexistence rather than eradication is encouraged where possible. If that's not going to happen then rejuvenate the turfgrass by leveling the area and re-establishing a thick turf or ground cover tolerant to the site (shade-adapted, for example). Small numbers of burrow openings can be treated individually with insecticide dust (Sevin or permethrin). Larger infested areas can be sprayed or treated with insecticide granules to discourage the bees when the problem warrants a response. There is an interesting video clip of a digger bee at work in the lawn at University of Maryland "Bug of the Week" website.

Dear Expert Rick,
Thank you for your response. Your description provided seems accurate to the "symptoms" I am experiencing with the bees, however, I am concerned the bee doesn't reflect the images you provided, so I'd like to know if in fact I do have a digger bees that will mostly be just a nuisance. I was able to catch one in a baggie and got it somewhat lethargic to take a pic and then release. Unfortunately, the pic from my phone to the pc lost a bit of clarity, but I think you will still be able to make out the coloration. I would appreciate your follow up. If these pictures don't provide you clarity, I can text to you or bring a sample to the farm and home center. Thank you again.

I'm attaching a few additional images that resemble the pics that you forwarded. It's difficult for me to zoom in because there was some loss of clarity. I'm hoping these images may allow you to make a closer match. If you are still not sure it would be best to take your sample to the extension office in Lancaster.

I wish I could be more definitive on the identification but you need to be comfortable that it is not a problem.

Here is some additional info from the U of MD.

Mary Kay Malinoski, Extension Specialist, Home and Garden Information Center
mining bee
(More insects from HGIC)
Print: HG 104 Mining Bees and Ground Nesting Wasps
Mining, or digger bees nest in burrows in the ground. Unlike honey bees, mining bees are solitary bees. Each mining bee female usually digs her own burrow to rear her young. Large numbers of these bees may nest close together if soil conditions are suitable. Mining bees are not aggressive and seldom, if ever, sting. Sometimes large numbers of males will fly about the same spot for several days in a mating display. 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 shiny metallic green. Mining bee burrows may be located wherever there is exposed soil and good drainage. The holes are about 1/4 inch in diameter, and are sometimes surrounded by a small mound of soil. These bees are important pollinators and control should be avoided if possible. Long term control involves elimination of bare ground areas to discourage these bees.

Good luck. I hope you are able to enjoy the holiday.