It’s Not Just About the Flowers: The important role of sand and soil in where bees thrive (Ep. 84)
We’ve spent years telling people to plant more flowers for bees. But what if the real key to supporting them is hidden underground?
In this episode, Dr. Marissa Chase shares her research that challenges the widely accepted wisdom that if we plant the right species and create a colorful pollinator garden, bees will come. Marissa and her team spent time in prairies in the U.S. state of Minnesota investigating what really shapes bee communities. Their findings are surprising: soil texture, not floral abundance, is the strongest predictor of where bees live and thrive.
It makes sense when you think about it. Around 80% of bee species worldwide nest in the ground. Different bees need different types of soils to dig and build their nests. Marissa’s work shows that sand content isn’t just a background detail—it’s habitat.
Marissa also shares how challenging it remains to support rare and specialized bees in restoration projects. In her recent work, factors the team assumed would matter—plot size, seed mix, location—didn’t change which bees showed up. The same common species kept appearing, no matter what was planted.
It’s a reminder that if we want to support the full spectrum of native bees, especially the specialists, we need to think beyond flowers.
Marissa is an an assistant professor at Villanova University. You can learn more about her work, follow her on Instagram or read the study we discussed.
Good to know
Marissa mentioned work she’d been doing on a rare specialist bee called Colletes andrewsi. Its known distribution are tall grass prairies in Minnesota. It specializes on alumroot, more commonly called heuchera. This is a largely evergreen perennial group of plants found almost exclusively in North America.
Transcript
[00:00:00.180] – Jacy
Welcome to The Bee’s Knees, a podcast wild about native bees. Wild and native bees are under threat worldwide. In each episode, we look at actionable things we can do to support these adorable little guys whose pollination work is crucial for maintaining biodiversity. I’m Jacy Meyer, and I thank you for being here. Imagine you and your friend are both describing your dream homes. There might be some similarities, but I bet each of you would have a list of must-haves that are different. For bees, home works the same way. Today we’re talking to Dr. Marissa Chase, who’s going to upturn some bee assumptions for us: that floral resources are the main driver of where bees live. Her and her team went out into Minnesota prairies to to test how sand content and floral abundance shape bee communities. And what they found is surprisingly simple: the ground matters. A lot. Soil sand content, not floral availability, was the strongest predictor of which bees showed up. I started our conversation by asking Marissa what this reveals about how we should think about habitat needs for wild bees.
[00:01:20.950] – Marissa
Yeah, that’s a really great question and part of the impetus for this research. And so I think the main point and takeaway when it comes to habitat is, you know, that nesting needs and nesting resources are really, really important components of bee habitat. So, as you know, I’m sure, and talked about a lot on your podcast is, you know, often so much of the focus when, you know, constructing, you know, bee and pollinator habitat is flowers, and floral resources are really important. You know, there’s plant these plant species or use this seed mix. But from our work, you know, nesting resources are just as crucial and really need to be factored into bee habitat. So kind of the example I use when I think about this is like when we, you know, consider floral bee specialists, so bees that rely on specific plant taxa for pollen, and we want to make sure, you know, we’re putting in very specific species or, you know, genera of plants or whatever in our gardens or habitats for them. You know, we also want to be cognizant that bees also might be, you know, specialized on different nesting resources and, you know, they’re nesting specialists as well.
[00:02:34.440] – Marissa
And so I think that’s one of the biggest points our research makes about bee habitat.
[00:02:42.600] – Jacy
So one of the most surprising results was that the sand specialists weren’t limited to the sandiest sites. But also showed up in areas with only moderate sand. What does this tell us about how bees find and use nesting habitat across the landscape?
[00:02:59.040] – Marissa
Yeah, it’s funny because I think it’s one of those findings in research that leaves you with a lot more questions than answers. And so it’s a really great question that you asked. And to your point, we kind of came up with a few different hypotheses, kind of discussing, you know, how bees find and use nesting habitat. So specifically when it comes to sand and soil with, you know, ground nesting bees. So the first is really the simplest, and it’s just that sand specialists, you know, don’t necessarily need like the sandiest of soils to be able to excavate their, their nest. So essentially, you know, moderately sandy habitat will do. And so sometimes when people think about sand specialists, they associate them with, you know, dune systems or, you know, that really fine high— those fine high sand areas. But potentially it just could be that moderately sandy habitat will do. The second hypothesis that we discuss in the paper, and this most relates to actually being able to find those sandy habitats, is that potentially bees are really good at finding, you know, discrete sort of pockets of high sand patches and actually use those for nesting.
[00:04:13.430] – Marissa
So we came up with this hypothesis because all of our, our moderately sandy sites that we used in our research still had really discrete patches of high sand. So I believe they all had, you know, pockets of at least 80% sand. And obviously soil is much more, you know, heterogeneous across, across the landscape. It’s not just, you know, one type of soil texture. So potentially, we kind of hypothesize that they can really seek out and find those patches. And then the third hypothesis, which I think is definitely true but is not actually discussed very much at all, and it kind of relates to floral specialization in a way. So just how, you know, there’s this spectrum of floral specialization across bee species that I’m sure you’ve kind of talked about across different episodes, you know, you have monolectic bees that only collect pollen from, you know, just one single plant species. And then you have some floral specialists that, you know, are specialists on a whole family of flowers, you know, things like sunflowers. We also hypothesize that sand specialization could also sort of exist across this spectrum where, you know, some species really require high sand areas, you know, like dune systems, and only can excavate their nest in those those really high sand areas, and others might just need sort of a moderate amount of sand.
[00:05:41.840] – Marissa
And so this kind of sand specialization might just vary across species, across sand specialist species.
[00:05:48.430] – Jacy
So let’s talk a little bit more about bee diversity, because one of the expectations going into the study was that bee diversity would be highest in sandy areas, but that wasn’t the case. How do these results kind of challenge these long-held assumptions about where diverse bees’ communities alive.
[00:06:06.520] – Marissa
Yeah, I think, you know, that’s one of my favorite parts about this study is, you know, I was wrong. I fully admit it. I really did kind of expect to find the highest diversity of bees in these really high sand areas because these high sand areas that we worked in, these really were, you know, sand dune systems. You know, when I think about going out and sampling bees and I get really excited about, you know, who I’m going to collect and where I’m going to go, you know, I always will picture some really sort of sandy dune system. And I think that’s because, you know, most of the time when we are thinking about our ground-nesting species, right, which are, you know, 80% of bees worldwide, we think about them requiring sandy soils in general to essentially excavate their nests. So not just sand specialists, but ground-nesting bees in general, we think, still need sand in their nests. And in some amount of sand. And this is because, you know, sand is loose, you know, it has bigger grains than other soil textures, it has better drainage. And then also it’s often bare. So that makes it, you know, easier to actually dig and excavate the nest.
[00:07:17.120] – Marissa
But, you know, our paper found, at least in Minnesota, that it’s not the super sandy areas that have the highest diversity. Of bees.
[00:07:26.580] – Jacy
So given that floral richness didn’t significantly influence bee abundance or the proportion of sand specialists, how should land managers balance floral resources with attention to soil properties when thinking about what to plant?
[00:07:42.390] – Marissa
Yeah, that’s, that’s a great question. I think it’s mainly about practitioners and managers, you know, first realizing that floral resources are not the only factor that affects bee communities. You know, we talked about this, I think your first question, right? It’s like the soil, it’s the nesting habitat that matters. In the paper, we, you know, we do discuss prioritizing sandy areas for conservation. So that’s both, you know, moderately sandy and sort of those high sandy areas, specifically because they support specialized bees. So we looked at sand specialists in this study, but we also looked at floral specialization and we did find a lot of those specialists in those moderately and high sandy areas. But I think what’s also important for land practitioners and managers in general is that our work also shows that it’s a diversity of soil texture that matters too, because we essentially saw that different bee communities, the bee composition was affected by the amount of sand. So different bee communities aligned with the low, medium, and high sand areas. And so if you do want to support still, you know, the broadest bee community possible, then you do want a diversity of soil texture in any sort of land you’re managing or restoring.
[00:09:08.660] – Jacy
So what future research or on-the-ground actions do you think could most improve how we support sand nesting and especially other specialist bees?
[00:09:18.260] – Marissa
Yeah, I love this question. So, you know, on-the-ground efforts would be obviously, you know, kind of I said in the previous question, you know, prioritizing sandy habitats for land conservation. You know, it’s also managing lands, you know, effectively with prescribed fire and other, you know, different treatments to, you know, prevent woody encroachment, specifically, you know, in our system, in our prairies, in sandy areas. And there’s all that, of course, but it also comes down to sort of how we restore habitat we already have for bees. And the thing is, I don’t think we necessarily know how to do that well. And I’m just gonna like specifically talk about our prairie systems, you know, our tallgrass prairie systems here in Minnesota, but also, you know, across the Midwest and whatnot in the United States. I worked on this study actually here at the University of Minnesota where we looked at how to kind of best, you know, effectively restore bee communities. And we varied these prairie bee plantings that we installed ourselves by— we varied them by seed mix type, by planting size, and then we also varied them by installing them in different places with either, you know, high or low natural surrounding area.
[00:10:29.920] – Marissa
And so we wanted to like investigate all these different factors that you think about when you actually install a planting or install a restoration. And when I analyzed the data, you know, none of those factors actually mattered. You know, no matter what, we were just, you know, across our sites, across our treatments, across those factors, we were just attracting and restoring really common bee species. And, you know, it didn’t matter how big the planting was, which was really shocking, or how many flowering species a planting had. It was those kind of same common sets of species. From the regional pool that were across our plantings. And so when you looked at the data, you weren’t really restoring our, you know, our specialized or rare bee communities. And we definitely don’t know how to do that. And so I bring that up because I think when the— where the research comes in, because part of your question was about future research, I think we really need to do more studies really investigating sort of the natural history, the habitat association. So kind of like the sand specialist work and really you know, the population dynamics of these specialized species.
[00:11:40.570] – Marissa
And so continuing to actually look at the population level and the dynamics of those bees is really important, and I think where our field really needs to go.
[00:11:50.350] – Jacy
So in all your time working with bees and biodiversity, has there been a discovery or some other part of your work that has given you hope or made you feel like you were making a difference?
[00:12:01.740] – Marissa
Yeah, I love this question. Um, you know, I feel I’ve been so extremely lucky because I’ve gotten to do a lot of cool bee work in a lot of different systems. But more recently, I have really delved into population-level and population ecology work with bees. And I think it’s given me a lot of hope for our field just in general. You know, what’s pretty wild is, you know, despite what we know about bee declines, which I’m sure you’ve talked a lot about on this podcast, and, you know, all the amazing bee research going on, if you ask someone, you know, how big are different bee populations, you know, you ask them how do they fluctuate from year to year, if you were to ask them what factors affect bee population size, I imagine, you know, they couldn’t, we couldn’t answer those questions. And we actually only know the population sizes of less than 0.1% of all bee species worldwide. And then when you actually look at that work, which is really interesting, you know, a lot of that work, which I’m sure you could have guessed, has been done on, you know, our social bees, like bumblebee species, or our cavity-nesting bees, because, you know, it’s much easier to trap-nest them and actually look at their populations that way.
[00:13:13.220] – Marissa
And in these past couple years, I’ve been really trying to answer those questions I’ve kind of just listed by working with this rare specialist bee, Colletes andrewsi. Who is a specialist on Heuchera, otherwise known as alumroot. And we did this really, really exciting mark-release-recapture work, which is rarely done with bees in general, especially like our solitary bees. And we were actually successful in estimating its population size across 17 different sites that spanned Minnesota. So that’s across, you know, a very, very large spatial extent. And we did a lot of, you know, natural history work on this bee and are now really diving into its population dynamics, metapopulation dynamics in general. I think if you asked me 2 years ago if this work was possible, I think I would’ve maybe said no, but it is. And we have so much work to do really focusing on bee populations and their dynamics and life history. Because I think going back to my earlier point, That’s what’s really going to help us answer questions about, you know, effectively restoring specialized and rare bees, or, you know, answering how do we increase habitat connectivity for bees, or, you know, whatever the question is related to conservation.
[00:14:28.700] – Marissa
We need that work because there’s a lot of amazing community-level bee work out there, and that’s been the priority across our field. But we really need, you know, that population-level information to contextualize those really broad community-level patterns. And so I’m really hopeful and really excited about doing that work, and I really want to try to push that work forward.
[00:14:52.480] – Jacy
For many bees, the story starts underground. We often treat soil as a blank canvas, something that’s just there while we focus on planting more flowers. But Marissa’s research shows that soil texture, especially sand content, can shape entire bee communities Nesting resources aren’t unlimited after all. They can be the limiting factor. And Marissa pointed out that this opens the door to a whole new wave of research. What other soil traits matter? Can we design restorations that support both the flowers bees forage on and the ground they depend on to nest? Future work will help us understand how to match the right soils with the right species. And how to prioritize conservation areas that already have the nesting conditions specialists rely on. Because supporting bees isn’t just about feeding them, it’s about giving them a place to live as well. Thanks to Marissa for joining us today, and thank you for listening. If you’re enjoying The Bee’s Knees, I’d love it if you could share it with a friend. Until next time, think like a bee homeowner.