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October 03, 2023

43 Minutes

Guests: Leif Richardson

Tags: bees, pollinators, insects, staff guests,

Have you heard of solitary ground-nesting bees? Yes? No? Either way, this podcast is for you! Unlike honey bees or bumble bees that live in colonies, solitary bees do it alone and interestingly, most of them nest underground. Although they are common, widespread, and almost certainly living in your neighborhood and at times literally under your feet, most people know very little about them.

Guest Information

To help us explore the world of these fascinating bees is native bee expert, Leif Richardson. Leif works for the Xerces Society where he coordinates the California Bumble Bee Atlas and although his work focuses on bumble bees, Leif knows a great deal about this lesser-known group of bees.


Matthew: Welcome to Bug Banter with the Xerces Society: where we explore the world of invertebrates and discover how to help these extraordinary animals. 

Matthew: Hi, I'm Matthew Shepherd in Portland, Oregon.

Rachel: And I'm Rachel Dunham calling in from Missoula, Montana. 

Rachel: Today our topic is solitary ground nesting bees. Unlike honeybees or bumblebees that live in colonies, solitary bees do it alone. And interestingly, most of them nest underground. Although they are common, widespread, and almost certainly living in your neighborhood and at times literally under your feet, most people know very little about them. 

Rachel: To help us explore the world of these fascinating bees is native Bee expert Leif Richardson. Leif works for the Xerces Society where he coordinates the California Bumblebee Atlas and although Leif's research focuses on bumblebees, he knows a great deal about this lesser known group of bees.

Rachel: Welcome, Leif. Thank you for joining us today.

Leif: Thanks for having me. Yeah, and I'm calling in from Southern California for Riverside where I live and, and lead the California Bumblebee Atlas for Xerces.

Matthew: So, Leif, just to start, kind of with the basics, how many Native bees are there in North America?

Leif: So, I'm not sure how many are found in North America and this is because the experts, the taxonomists are still working on that number.

Leif: But I can tell you that in the United States, we think we have about just over 3,500 species of bees. And as an example of the diversity at a smaller scale in California, we have 1,600 native bee species. Roughly half a little almost half of what we find in the United States total. So this is a lot of diversity.

Matthew: Yeah, no, that one that's quite mind-blowing for someone who maybe thinks that there's like the honeybee, a bumblebee, and just a few. So to know that there's that many is quite remarkable. I mean do you know how you might how many you might like find in your neighborhood is there any indication of that?

Leif: I don't know of any work on this, but I can say that in very small areas, we expect that where there's intact ecosystems and good habitat, we can expect to find tens or hundreds of species. There's a famous example from about in the last 10 years there's a study from the Grand Staircase Escalante wilderness area in Utah where they found almost 800 species of bees and that's a relatively small I mean, it's multiple landscapes, but it's a relatively small piece of geography to have that many species.
And again, that's out of a total of 3,500 found nationally so diversity can be very high in all areas.

Matthew: Yeah. I mean, and of those how many, might be considered to be solitary.

Leif: Right, so I should say first. Solitary is to be distinguished from social living and, and you, you referenced honeybees and bumblebees.

Leif: So those are the best-known social species of bees. Honeybees of course live in hives for the most part and they come from Eurasia and Africa. They are imported here to North America as agricultural pollinators. And so they are not native insects here. They don't belong, if you will, in intact ecosystems of co-evolved native species, but they do occur there in many cases. They do they have naturalized and so they occur in natural areas alongside these native bees. Bumblebees, there are about 50 species of native bumblebees in North America and so those are social bees that also occur here alongside the solitary bees.

Leif: Now, interestingly, something like 75% of all of those bees are solitary. So the social lifestyle that we all have some familiarity with and some understanding of in terms of talking about queen bees and workers and things like this. That's, that's the exception rather than the rule and in the world of bees. 3 quarters of them are actually solitary.

Matthew: What do you mean by solitary? Is there an easy way to describe what that might, what life might be?

Leif: Yeah, so the typical lifestyle of a bee is not the one where there's a queen and her offspring who are doing the work for her. Instead in a solitary bee, there's actually no cooperation between individuals. There's no division of labor among what we call casts.

Leif: Again, like a queen, a worker, a male or drone, those are casts in the honeybee lifestyle and we don't have that in solitary bees. There's no foregoing of reproduction to help related individuals reproduce.
So in the case of honeybees, the workers are females who do not mate and do not reproduce.

Leif: Instead they help their mother reproduce. So there's none of that in the solitary world. There's very little social behavior in general because most of the life of males and most of the life of females is spent solo. And importantly, there's no meeting of offspring by the mothers.

Leif: So there's no opportunity for social behavior to evolve because the mothers never meet their offspring. There's no way of communicating. There's no way to sort of, causing your offspring to work for you so that you can produce more.

Matthew: Is there a reason why the mother doesn't meet the offspring?

Leif: Yeah, in most cases she, seals up the nest and flies away, maybe, maybe creates new nests, but, or maybe just that one and eventually dies.

Leif: And usually the offspring do not emerge from that nest for months to a year. And so there's this strong bifurcation where the adult bees do one thing they finish their lifecycle and die whereas the eggs becoming larva and eventually pupa or cocoons, they're going to become active in the following, season.

Matthew: Okay. That's, because it's not just like the parents are tired of their kids and they're running away.

Leif: No, but I should say solitary bees. So all of what I just said is accurate about them. However, many of them will nest in aggregations. And so you will find tens, hundreds, even thousands or tens of thousands of nests all right next to each other. Usually expressed as holes in the ground with a little pile of dirt that the bee has excavated from the ground. Those bees are all solitary females who are making their own nests, they're just doing it right next to neighbors and there may be some sort of social behavior that goes on between neighbors.

Leif: But for the most part, these are solitary bees producing their own nests and they just prefer to aggregate. You could think about some birds that do this too, like swallows will often aggregate in their nesting.

Matthew: Yeah, you know, I have to admit that I have a really strong memory of sitting in the middle of a mining bee ground nesting site and somebody's garden orchard and we calculated that there were about 50,000 nest entrances in that area and just sitting there with the hum of all these bees flying around. And yet knowing that they were just individuals getting on with life and were no threat at all to me.

Matthew: For some people just the idea that you're sitting in the middle of thousands of bees would be an unnerving thing.

Leif: Yeah, maybe we should say, I should say that, that solitary bees can sting like honeybees and bumblebees can sting.

Leif: The males cannot sting so the half of the species can’t sting you and then of the females for many species the sting is negligible pain or they’re sort of docile and they tend not to sting.

Leif: And so these, these animals are really safe to approach. And I don't recommend that you try to pick them off of a flower or something, but as Matthew says, you can go to an aggregation and sit down and watch and you're not going to get stung.

Leif: You're just another obstacle. Like a tree or a rock or something that they have to fly around but they're they don't see you as a threat per se.

Matthew: So, Leif, I think some of our audience might be really shocked to hear that male bees don't sting. Is that just for solitary or can you clarify is that for all male bees that no male bee can sting.

Leif: That's for all bees. And the reason is that the sting is a modified ovipositor. An ovipositor is the egg laying structure of females. So obviously males don't lay the eggs, they don't have that structure that then evolved into a venom delivery system.

Leif: So this thing is there's a sack of venom and it's attached to that egg laying device. And the bee sticks it in you and squeezes and the venom goes into you. That's how it works. And so male bees sometimes will mimic the females if you handle them. The males will mimic the females if you handle them.

Leif: In bumblebees, the males will buzz a lot. They'll work their abdomen as if they're poking you. But of course they can't. They act like they're going to hurt you but they simply can't.

Rachel: That's so interesting. I actually just learned this fact. This past year I was giving a talk and it blew my mind. I knew that male bees can’t sting, but I didn't realize that it was the reproductive parts of the female that was the stinger. So thank you. I think that's I think that's super interesting.

Rachel: I want to go back and ask you a question. You know, you think about social bees versus solitary. What's the evolutionary benefit of being solitary? Do you think these females are out there gathering pollen and nectar for their offspring by themselves rather than having this colony of help. What's the, what's the benefit there? Is it the habitat that they can find is different?

Leif: Okay. Well, we know, we think that the ancestral condition for all bees was nesting in the soil as a solitary bee as a solitary insect. And this is similar to lots of their relatives, lots of other insects that, that are nesting in the ground and that sociality evolved multiple times in the lineage of bees over the last many millions of years. It evolved from solitary lifestyles and in some cases, bees may have reverted to solitary living.

Leif: Again, so I'm not sure if there, if we could say there are advantages, intrinsic advantages of solitary living over social. It's different ways of making a living and there's lots of theory about how social behavior is an improvement over the solitary lifestyle or that it that it works in some environments and not in others. So we can think of being solitary as kind of the ancestral condition for bees and it's how they started out.

Rachel: Interesting. Well, let's start talking about ground nesters then if that's how they evolved is these solitary ground nesting bees. So obviously there's more than just the ground nesting solitary bees of all the solitary bees, how many of them, what percentage of them nest underground.

Leif: Yeah, so actually most bees nest underground. I'll say that they nest bees in general, for general places. One is in the soil, in the ground. Another is in wood, so they may excavate solid wood like a carpenter bee does or punky rotting wood like some of the halictid bees do. Or they may live in twigs with, with a pithy center that's easy to excavate.

Leif: There are bees that use pre-existing structures. Sometimes they are referred to as renters by bee scientists. So, and then finally in the fourth category would be above ground builders. So, bees that, build structures above ground out of mud and pebbles, glandular secretions, perhaps nectar and pollen. So they build the architecture of the nest, but they do so above ground. So, it's estimated about 65% of the solitary bees are soil nesters. So soil nesting of those 4 life histories or lifestyles is the most common way that a solitary bee lives.

Matthew: But about how deep might these nests be? Because I'm just trying to picture a small bee. Starting with a patch of dirt. I mean, are they just like going like a dog and scrabble with their legs and like kicking the dirt out behind. I mean, it seems like a lot of effort.

Leif: Yeah, there's a whole bunch of fascinating biology here. Many species of solitary bees have adaptations, morphological adaptations for digging, and for soil moving, for plowing essentially.

Leif: And so they will first take a crack at the ground surface, which is often the hardest part that they have to dig through. And then they dig through softer soil going down into the earth. It is amazing how deep some of these bees go.

Leif: I saw an average depth for solitary bees at about 35 cm or maybe 12 to 14 inches.

Matthew: Wow. 

Leif: So that's not too deep, but remember that bee has to dig that hole as a single little insect and remove all of that soil to the surface and do something with it.
And there are bees that nest much deeper. So there are reports of a bee that can nest up to 5 meters deep.

Matthew: Wow.

Leif: So this again is a single bee digging this very long tunnel into the earth. Carrying all of that dirt back at the surface and disposing of it. There's even a case where of a species that nests at something like 2 to 3 meters and only lays a single egg in each of those nests. So they have to dig a whole nest just to make one offspring. Most of them as I'll probably say in a minute here, most of them will lay multiple eggs in a nest.

Leif: So there's some conservation of labor there.

Matthew: Yeah, I'm just thinking about how long is a bee - half an inch long and it goes down 25 times its body length. I mean, I'm trying to imagine me digging a tunnel that long.

Leif: Well, many of these, are a lot smaller than a half an inch. Maybe a half to a quarter of a centimeter. It can be very, very small. And yeah, some of the bees, the depth that they dig to and the volume of soil that they move. If we were to scale that up to a 6 foot tall human being, it's just amazing.

Leif: I don't have the figures on hand, but, they’re doing an incredible amount of earth moving, that would take you many lifetimes to pull off.

Matthew: Well, yeah, even the simple calculation puts it well over a hundred feet deep for a person my size and it's just incredible Okay.

So digging turns out to be one of the core functions of being a bee. And, and we certainly think about that when we think about bees, right?

Leif: Your first thought when you're considering what a bee is probably involves flowers and honey but, think of them instead as these, fossorial or digging animals that do a lot of their life - they pass a lot of their lives below ground in the dark and doing things that we can't observe very easily.

Matthew: Yeah. I mean, how, long does it take a bee to dig a nest. I mean, I realize that there are thousands of species in different depths. Is there a sense? Do they do they do it in an hour or a day or a week?

Leif: It is variable, of course. I have seen figures of, some bees taking less than a day to, dig their burrow others taking 2 days or more. But I would say just a very general average is probably about a day to excavate a nest.

Leif: And the nest architecture I should just say it's generally a burrow going vertically down into the earth. It might go diagonally or sideways, but generally it's going down and the burrow has tunnels coming off of it, usually, or often horizontally. And then those tunnels terminate in brood cells. And a brood cell is where the action takes place.
This is where the mother lays the egg. It's where the mother provisions with nectar and pollen, sometimes with floral oils, and then lays an egg right on top of that.

Leif: The brood cell is often lined with this special material that the bees produce with glands that we can talk about more if you're interested but they that has all sorts of interesting functions in terms of waterproofing and keeping on pests and microbes.

Leif: So, so think of that vertical burrow with lateral tunnels coming off of it and each tunnel terminates in a single brood cell that is single in most cases a single egg is laid into.

Matthew: Wow. Yeah, definitely. I mean, say, talking about the, substance that they line it with, it seems like if you're underground. And it rains. Do the cells filled with water? I mean, there must be some way in which the bees keep their offspring safe because you're saying that they're probably in that cell for a year maybe.

Leif: Yeah, yeah, it's a great question. And, let's see what we know about this.

Leif: There are documented cases where solitary bees nest aggregations have been impacted by flooding.
So, they’re at a nest aggregation, a flooding event occurred, and they went back and saw that a large proportion of the nests had failed. Water just flowing into the burrow and drowning the bees.
So that must be a risk for bees that live in tempered areas at least where rain could be expected.

Leif: But they have an array of different ways of dealing with water. The most interesting to me is that they secrete these glandular products that they can they use to line the brood cell. Some of them are waterproof. So bees that live in wet environments will often use a waterproofing that the offspring is going to be inside of that waterproofing completely safe from the outside.

Leif: Water can stream down around them and just they are fine. In fact, some of these bees they choose to nest in soils that are seasonally inundated. So there are months when that little brood cell with a larval bee or a pupa in it is completely inundated. There's water on top of them and probably the soil is saturated around them. Oxygen is limiting. There are numerous cases where these, this is part of the process. This is not a mistake, it's not a rare flooding event. This is where they nest like in one example that comes from the southeastern US.

Leif: They're nesting in that sort of muddy bank that you see on a vernal pool, that sort of intertidal of the vernal pool, they nest there and then seasonally the thing fills up and that's how they're inundated.
So, so bees have a variety of ways of staying dry in the nest. And I would say that most of them probably come from these glandular secretions that they make.

Matthew: Yeah, because I have heard about polyester bees and I think they're the ones that they kind of like a cellophane like material. That completely lines it.

Leif: That's right. Yeah, those bees literally make, cellophane the same product that human beings figured out how to make from hydrocarbons of some sort. And bees they make it just a wild array of different materials that they're using in the nest for waterproofing and for pest control and other things.

Leif: So the environment they choose to live in dictates that they need some of these defenses and they're both of these interesting ways of avoiding mold, avoiding flooding, avoiding parasites.

Matthew: Yeah, that's amazing. They really are amazing insects. 

Rachel: So these ground nesting bees, do they use materials other than what they secrete and do different ground nesting bees use different materials based on the type of bee they are?

Leif: Yeah, there's a great variety of ways that they make a living. So let's see. The simplest way they're excavating the nest. There are some species that do not line the brood cell as I just described. So the simplest way is maybe they have the next nest architecture that I described but no brood cell lining and the egg the pollen is deposited on the dirt in the in the little cell. The egg is laid on top. The cell is closed and that is it. But other bees will use, as I said, glandular secretions that they produce from their bodies. And there's a gland called the Dufour’s Gland, which is important in this respect. There are some other glands that produce these things. 

Leif: Bees will also use plant products to line their nests. We know that plants contain a wild array of secondary metabolite chemicals that include some of the things that make our food tasty, make our food toxic. That accounts for our drugs and plants so these plant chemicals are everywhere in the plant world and bees encounter those including in nectar and pollen.

Leif: But so we see, so we see these gathering some of those plant chemicals from plants and then and then incorporating them into the nest as maybe antimicrobials or anti parasite chemicals. There's even a linear, a lineage of these that use cut pieces of leaves or flower petals to line the nest. And so you can actually see the mother on the plant excising an oval piece of leaf material. And then she flies home carrying this big, unwieldy flat circular thing. And then gets inside the nest with it and uses lots of those to make a sort of like a bouquet of overlapping leaves or flower petals and then the egg is inside of there. So many ways to make a living as a solitary bee and I would say plants are often a part of this picture.

Matthew: Yeah, the way you describe it makes me think of the mother whose taking great care of her kids. I came across someone who once a likened that sort of parent putting wallpaper in their kid’s bedroom to try and create this this lovely sheltered comfortable spot for their offspring.

Leif: Yeah. One thing that's still amazing to me is bees, so solitary bees don't have huge fecundity. They don't have huge reproductive output. We tend to think of insects in that way, like, a plague of locusts.

Leif: It's millions of animals that suddenly sprung out of nowhere. They reproduce very quickly in a few generations they were able to produce this exponential growth. That's an idea we have about insects. But, solitary bees are different. It's estimated that a single mom, may lay an average of 10 eggs total in this nest. And so that's not exponential growth. You know, you're going to lose some to parasites and to weather or whatever.

Leif: And so when we think about bees, it's sometimes beneficial to think of them more like bears or birds. In terms of their fecundity, then to think of them like flies or locusts where it seems like it's the exponential growth is possible at any time.

Matthew: Yeah, because again, we're thinking of honey bee hives full of thousands of bees, aren't we?

Leif: Yeah, that's right.

Matthew: And all that honeycomb and we're not thinking of these little holes in the ground, with a few brood cells.

Leif: That's right. Yeah.

Matthew: Yeah, I mean the other thing that makes me wonder, I mean obviously digging the tunnel is hard work. May make the excavating brutal, but there must be a lot of work going into the foraging too.

Matthew: You know the nectar the pollen that the mother brings back to supply the brood cell. I mean, how many did we know have a sense of how many trips it might take or how long? I mean, again, I, I think in terms of hours or days because that's, that's the clock I work on but I don't I don't know how bees measure time, you know.

Leif: Yeah, the first thing to say is that, is, that bees eat just a few things. They virtually all of them eat pollen, which comes from flowers. And this is distinctly different from the closest relatives, the wasps.
And then some other relatives, ants, where they all, with very few exceptions, are eating animal protein. They're feeding animal protein to their larval offspring. Bees are vegetarians.

Leif: This is one of the reasons that bees are distinct from wasps. They evolved this habit of eating pollen and feeding pollen to the larvae instead of feeding animal protein like a like a caterpillar or a spider.
Something like this. There are bees that also use other plant products, floral oils. And indeed, there are plants that are co-evolved with these bees. They probably produce the oil because the bees need the oil.

Matthew: So, how many trips does it take for a solitary bee to fill up its nest?

Leif: There are estimates that, it could take as little as 2 trips for some species. They carry a lot. It takes a couple of trips, but, it's probably more like an average of 10 trips. And there are documented cases where it takes 40 or more trips for bee to bring enough pollen to feed one offspring.

Leif: So, if you get the opportunity to watch an aggregation of soil nesting bees or perhaps, twig nesting bees above ground are easy to watch. You see the female continually leaving and coming back loaded down with pollen spending five minutes in the nest. Then appearing without the pollen, taking off, returning 20 mins later. It is a ton of work.

Matthew: Yeah, I mean, I've now got this image in my head of a, being a vegan wasp, which I think is cool.

Leif: Yeah. That’s it

Rachel: So we just, I think about, you know, these hard-working female bees, you know. Going into the ground and laying their eggs and getting the materials they need and doing everything they can protect them. And I just think about what are the potential impacts that they face of our actions, I think of pesticides being on the plant materials that they're taking into their nests and the pollen and the nectar.

Leif: Yeah, so, solitary bees are threatened by a number of different factors and we know that some of them are declining. I should say though that for most solitary bees for most of the 1,600 species found in California or the 3,500 or so found in the US. We don't know much about them. We know they exist. They've been formally described and there are some specimens on pins and museum drawers but we don't know very much about their life history or where else they occur besides those places they were found.

Leif: So it's hard to say what just how dire the problem is for solitary bees, but we can extrapolate from the bees when we know better the bumblebees, about a quarter of those are in decline and at risk, some a great risk of extinction.

Leif: So I would guess that the situation is similar for these solitary bees. But it's scary because we don't even know what we’re losing in this case we humans trying to conserve this stuff we don't even know which species are pitched on the brink of extinction and we could actually step in now and do something about it.

Leif: So what is threatening them. Well you're right the pesticides are a major issue and bees encounter pesticides on flowers when they're foraging. They're sprayed over the top of the flowers. Or they're sprayed on the ground and the chemicals are systemic. So they come up through the plant and they're expressed in all plant tissues and products including nectar and pollen. But bees are exposed in other ways too. And one of the ways that solitary ground nesting bees are exposed to pesticides.

Leif: Well, two, I'll say. One of them is materials like leaves and another is the soil itself. And until recently, we were not thinking about these as risk factors for solitary bees in the context of managing and regulating pesticide chemicals.

Leif: So EPA does not look at whether, a bee is a soil nester and therefore could be exposed to pesticide residues through the soil or the residues landing on the ground and eventually coming down into the soil. So soil born exposure is likely to be a major issue when these bees become exposed to pesticides.

Leif: It's completely off of our radar until the last couple of years. And then these leafcutter bees that I briefly described, similar situation. We think a lot about what's in the flowers and what bees are becoming exposed to in the flowers. We rarely think about the leaves, but remember that bees are herbivores just like caterpillars that are pests of crop plants let's say. These are herbivores they feed on plants and they also cut leaves. They don't only eat, pollen nectar sometimes they eat the leaves. So we do need to think about that as a way that they become exposed to pesticides. There are many other threats to bees and I would include there, climate change.

Leif: We have good evidence that climate change is affecting bee populations, habitat loss is a huge factor for bees. And with these ground nesting bees you can easily see how losing that type of habitat the ground itself to development to paving to impervious surface is the end of the road for them so they are losing flowers but they're also losing these nest sites.
Yeah, and it seems like the nest sites are really important. Since that's where the bees could be for a year.

Leif: Yeah. And this seems so sad in a way that the mother bee is putting all that effort into feeding and supporting her offspring, trying to create this safe place for them and yet inadvertently is potentially bringing in toxic food, toxic wallpaper. She's bringing in the toxin. 

Matthew: Like it seems like such a sad image to leave people with, isn't it?

Leif: It is and talking about bees is sometimes a bummer. There are some things that we'd rather not be true but one of the things we do at Xerces is talk about imperilment of invertebrates and second, what are the approaches that we scientists and you the general public can take to address these problems? And so thankfully we know something about these issues.

Leif: These challenges that bees face and lots of people are working on solutions. I think that some of the problems are going to require more than a sort of a technical fix like a fix in the agricultural context to reduce pesticide exposure, like a different type of spray nozzle.

Leif: These are sort of what I mean is like technical fixes but consider climate change. Consider changes in the precipitation and temperature regimes of a climate a place.

Leif: We need to do some really heavy lifting to save bees that are imperiled by those changes. And as far as I can tell that is not happening fast enough for. 

Matthew: Is there anything that we can do?

Leif: Yes, of course there are lots of things that you can do. Let's see, if you, have a garden, if you have, if you own land, if you have a backyard that you can plant things in, plant flowers. That is a great idea.

Leif: More importantly, plant native species wherever you are try to figure out what are the native plants that bees might be attracted to here where I live. Which ones of those are available in the horticultural trade and put those in your garden.

Leif: It's not that non-native plants are bad for bees. It’s funny that nonnative bee plants are really attractive to native bees and can be very valuable to them. But in general, we think that native plants are better food sources for the bees that co-evolved with them. And there's one specific reason that that's especially true and that is that a substantial fraction of all bees are host plant specialists, meaning that they, they gather only a restricted set of pollen species to take back to the nest.

Leif: For some, there's a single plant they can use. A good example, there's a bee called the Mojave poppy bee that lives in the Mojave Desert here in Eastern California. There's only one poppy plant species that they can, they can gather pollen from. They will not use any other plant. This plant is federally listed as endangered. It occurs in only a few dune fields. And so you can see how there's here's another conservation issue. These specialists. There are other specialists that use one genus of plants or even a family of plants.

Leif: But the point is that they have a restricted set of host plants that they can use if you plant natives you're more likely to include some of those plants in your garden. And I would encourage people to take a step further if they're interested in providing food for bees and that would be to think about trying to find out what are the host plants for specialists in my area.

Leif: You can Google around or you could get in touch with me if you want and I could help you with that. But, you can find lists of plants that are especially good for these specialist band some of them are available to you for growing and that might be a good idea.

Leif: I'll say if you don't have land of your own, you can still make a difference in many ways, right? You could start a community garden, something I’ve done many times when I didn't have my own plot of dirt.
It's a wonderful experience for a human being and it is also a place, a way that you can you can plant the things that these bees need. You can address some of the other threats like pesticides through your spending and eating behaviors. And so if you care about bees and you're concerned about pesticide exposure for bees.

Leif: The best thing we can do for that for in that case is to grow food without the use of pesticides or these pesticides that are toxic to bees. And the reality is we can't grow all of the human food supply that way right now, but, but there is a lot of organic food available out there or food that's grown without intensive use of these chemicals. 

Leif: I would encourage you to think about how you spend your money, what you put in your mouth as ways to conserve bees. And I really hesitate. I don't want people to feel like this is a, you know, you have to have enough money to be able to take this step to save the bees. There are ways that everybody can think about their own diet and probably make a difference.

Leif: And of course climate change we've already discussed, but this is a, this is a problem with only one you know, we need to do more to work on behalf of, of the bees in this regard.

Leif: Yeah, I would think it's really important that people understand that, you know, you don't have to do everything at once, but there's something that you can do right now. And if we each take a small step. Then collectively we can we can begin to have an impact. I should say also that. Something you can do, to support bee conservation is to, is to support, organizations like the Xerces Society.

Leif: I don't want to make a pitch for us for you to donate to us, but I will say that scientists, but yeah, but this, like some of the other organizations, we are doing some of the foundational research, that is necessary to figure out which bees are rare and necessary to address their issues. So I think it's a great idea to support scientific research and conservation action. If you can't do it yourself, you don't have the option to plan or to spend differently or whatever.

Rachel: So, Leif, my husband and I just recently moved here and bought a house and I'm not a natural gardener. I kill most plants. I'm shocked I have any house plants alive still. And I have put some native plants in. I'm really excited and really proud of that. But are there other things other than planting that people can do?

Rachel: Maybe folks are really not into putting plants in the ground, but they have heavy mulch. You know, we're talking about these ground nesting bees. You know what would be helpful like what do they need to get into the ground are there kind of maybe lazier things that people can do?

Rachel: Because those are really nice to be able to do the lazy stuff. And really know you’re helping the invertebrates out there.

Leif: Yeah, so we're talking about soil nesting bees. There are many different types. As I've said, and so lots of different ways of making a living as a solitary ground nesting bee, but they all need to start at the surface and dig down. And so for many of them, they prefer some bare soil that doesn't, isn't densely vegetated. It's not a lawn with grass.

Leif: So, you will often see people recommending that to help those bees you might you might maintain a little area of your backyard. In a fashion so the bees can find it and easily get into it.
In some cases, so bees will nest in many different types of soil. And some of them are somewhat generalized in what soil textures they'll accept. Others are specialists, in particular sand bees. There's a group of bees that prefer to nest in sand dunes and other types of sand substrates and they won't nest in your backyard if you don't have that sand.

Leif: And so some people have figured out how to attract those bees by actually bringing in the sand, creating a level terrace of the right habitat that's packed the right way.
And then whether you seed it with bees or they come naturally, they find the habitat and they are using it.

Leif: So there are things like this that you can do. We think that in general that leaving some if you have deciduous trees in your in your yard, leaving some of the leaves in the fall on the ground is probably beneficial to these bees. You maybe want to pick up the leaves and so a way that you could kind of have both things that tidy yard and the bees is maybe leave some patch, some area that you don't manage.

Leif: You just let the leaves sit there on the ground and rot. And this is because some species of bees will, they'll nest under the, the leaf litter. So I've watched them go down between the leaves and if I move the leaves away there's the beautiful little hole that the bee is going for.

Leif: So in some cases we want to leaves and some other rotting vegetation on the ground. And then this is not about ground nesting bees, but many bees, as I said earlier, nest in twigs above ground. And so things like brush piles, messy piles of sticks in your, next your compost pile.

Leif: Or the back 40 that you don't take care of every year, you know, an old field or a small piece of forest that’s regenerating or something. These are all really great places for bees to find nesting substrates above ground. So think about incorporating some dead plant material above ground in your habitat if you'd like to support those bees also.

Rachel: Good, we did all those things now I’m feeling even better about it.

Rachel: Well, thank you, so much for all of this just incredibly amazing information. We like to end on asking folks this question. What inspired you to get into this line of work to get into studying these fascinating bees?

Leif: I have a long-standing fascination with plants. As a child, I was interested in plants. I was a nerd and like to go outside. And learn the trees and things like this as a pre-teen and teenager. And I guess as I got older I would in college I was I was thinking I was going to be a botanist or something and I did a study of plants where the question was is there floral mimicry which is the situation not very well described but it definitely happens where one species of plant will evolve to look similar to another over long periods of time, but it won't have a reward for the pollinator. Nectar, let's say. And so the pollinator will get confused between the 2 plants and will inadvertently land on the non-rewarding mimic.

Leif: And in so doing, will transfer pollen back and forth between the flower, different flowers of the mimic. So I was trying to figure this out and obviously the bees were doing the moving of the pollen in this system and I knew nothing about bees at this point and I just became obsessed with bees. What they're doing the way that plant production takes place is really fascinating that they're they need a handmaid they need an interloper to move the pollen grains back and forth not all plants need this but most of them do and it just the dependencies there the mutual dependencies there and also conflict in terms of what they're, what they're doing, the bee is foraging for her food, the plant is trying to reproduce. These are 2 different things and they're often at, they're often opposing, forces there that you can't necessarily have both things at once and so.

Leif: Yeah, I, that's what really got me into bees. And I will say, a second thing about it is that, plants make all these chemicals and I think that is a really fascinating part of plant ecology.It's also a fascinating part of human ecology. But, when you really look at bees, you find that bees are using plant chemicals constantly.

Leif: They're using them as antimicrobials as food as pheromones. There are bees that gather plant smells to smell better for the opposite sex. Are you using plant chemicals in all kinds of ways and at a certain point in my development as a biologist I realized this is really where the action is. This is so cool that the plants are able to manipulate the animals through floral odors and through other kinds of odors and through toxic chemicals at different concentrations. Daily changes and how much they apportioned different structures and that the bees in some cases need these chemicals and sometimes they are exploiting the chemicals for their own uses and not helping the plant in some kind of way. There's this really cool interplay between the plants and the bees that I think is mediated by chemicals and, that is just really fascinating. So that's my story of why I'm really interested in bees.

Rachel: Well, I think it's great.

Matthew: Yeah. I mean, it just that story in the end was captivating enough. That was amazing.

Rachel: Well, thank you so much, Leif, for your time today. It's just been wonderful having you and I've learned a lot.

Rachel: I hope you've had fun too.

Leif: I've had fun. Thanks for having me.

Rachel: Bug Banter is brought to you by the Xerces Society, a donor-supported nonprofit that is working to protect insects and other invertebrates -- the life that sustains us.

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