There are around 4,000 species of wild, native bees in North America, though imported, domesticated honeybees seem to be the bees that get all the attention when it comes to conservation. To help us learn about native bees and their value, joining me on the podcast this week is entomologist and wild bee expert Dr. Jessica Forrest.
Jessica studies the evolutionary ecology of plant–pollinator interactions. She started out as a professor at the University of Ottawa in 2013. She is now tenured and teaches, conducts research and leads Forrest Lab, which includes supervising the research of graduate students. “They and I work together to advance the research program, advance our understanding of wild bees and other pollinator populations,” she says. She also teaches ecology courses on population and community ecology and plant-animal interactions, and teaches a field course in Colorado called “Alpine Ecology.”
Jessica Forrest, Ph.D., is an entomologist and wild bee expert who teaches at the University of Ottawa, where she also runs the Forrest Lab. (Photo Credit: University of Ottawa)
“I have always loved nature, and that includes insects,” Jessica shares. Her first professional encounters with insects came when she was an undergraduate student. “I worked in an entomology museum, and there we were studying the diversity of flies,” she recalls.
It was the Lyman Entomological Museum at McGill University in Montreal.
“I looked at thousands of tiny, tiny flies under the microscope, and the diversity, the beauty, intricacy of all of their little structures was amazing to me,” she says. “You don’t appreciate this when you look at things in the field. You really have to see them under a good microscope to appreciate that.”
To the human eye, small flies can be indistinguishable from each other. Under a microscope, species can be told apart a number of ways, including by looking at the veins on their wings.
“Each of those veins has a name, and the position and presence and cross sections of those veins, that’s very important in insect taxonomy,” Jessica says.
She says she is sure there is an adaptive significance to all of these traits though for the most part that significance is not obvious.
Whether or not a fly has bristles on its body, and where those bristles are located on the fly’s body, is another way to identify a fly.
“Then there’s also things just like overall body shape, whether they have grasping legs for catching prey or for holding a mate, whether their mouthparts point forward or down, how long the antennae are. There’s all kinds of things.”
That experience increased her appreciation of insect diversity, but she wanted to do more than work on dead specimens in the lab — in the basement of the museum.
“I really wanted to do some work that got more at insect behavior,” she says. “And I always thought that Hymenoptera — the order that includes the bees and wasps and ants — was a really fascinating group of insects. And of course, bees are so important for their role as pollinators.”
Native Bees Vs. Honeybees
For a long time, it seemed like the honeybee was the bee that got all the attention — as if it was the only bee out there. But I think we’ve graduated from that, and we now know that honeybees are just a small fraction of the world’s bee diversity.
The European honeybee, which was introduced to North America from Europe and Africa, is one species compared to 4,000 native bee species in the United States. There are about six or seven honeybee species found worldwide — most of them in Asia — and 20,000 bee species worldwide, with a huge variety of life histories, behaviors, diets and habitats that are really not reflected in the biology of the honeybee.
While honeybees live in hives, the majority of bee species in North America and elsewhere are solitary bees.
“The female mates with a male but then works on her own to make a nest to provide pollen and nectar for each individual brood cell — a brood cell being basically a chamber for an individual egg that will grow into a larvae and then eventually an adult bee,” Jessica explains. “So she does all of that on her own. There’s no help from sisters or daughters or anything like that.”
There are some native social bees, such as bumblebees and green sweat bees, which live in colonies and hives.
Solitary bees foraging on willow catkins in early spring.
(Photo Credit: Jessica Forrest)
Bumblebees
Honeybee queens can live for several years and are always surrounded by worker bees. Bumblebee queens are the only members of a colony to overwinter, continuing an annual colony life cycle.
The large bumblebees that you notice in spring are the queens foraging for pollen and searching for a new nesting site: flying slow over the ground, looking into every possible hole to find a good place to start a nest. They may nest in an abandoned mouse burrow or a cavity in a rock wall.
“They’re looking for existing holes,” Jessica says. “They don’t dig them out themselves.”
The queen gathers pollen and nectar into a pollen ball, lays eggs into the pollen ball, then sits in her nest and incubates her brood.
“Initially, it could just be a handful of workers, but once they’re mature, they will come out and take over the foraging,” Jessica says.” … The mature size of a bumblebee colony could be a few tens of workers to a few hundred, but nowhere near the size of a honeybee hive.”
A typical honeybee hive can contain between 20,000 and 80,000 bees.
Bumblebee colonies are not conspicuous. One or two workers go in and out at a time.
“The only time I’ve really noticed bumblebee colonies in nature is when they switch to their reproductive phase late in the growing season,” Jessica says. After the hive reaches a certain size, certain number of workers, and maybe in response to environmental cues, late in the summer, bumblebees switch from producing workers to producing new queens and male bees. “All the workers are females. There have been no males in the picture until late summer.”
If you see a bumblebee snoozing on a flower, that’s likely a male. Once males leave the colony, they don’t go back.
“Once these new reproductive bees are produced, they will start coming out of the colony in pretty large numbers. And so sometimes you will see a nest entrance that’s got a bunch of male bees just coming out for the first time,” Jessica says.
A queen bumble bee (Bombus nevadensis) visiting larkspur (Delphinium).
(Photo Credit: Jessica Forrest)
Carpenter Bees
Carpenter bees look a lot like bumblebees but they are a distinct genus. However, they belong to the same family as bumblebees and honeybees, Apidae.
Carpenter bees are mostly solitary, though they have a complex, intermediate social system. The daughters of a female bee can help with reproduction, but carpenter bees don’t build full-fledged colonies.
Carpenter bees have hairy legs but a hairless abdomen, which helps to distinguish them from bumblebees.
Parasitic Bees
Parasitic bees are solitary bees that don’t construct their own nests but rather look for existing nests to lay their eggs in, as a cuckoo does in the bird world. The parasitic bee egg hatches before the host egg, kills the host egg, and then eats the pollen and nectar that the host mother provided.
“The parasitic bees, they’re very different in their behavior from non-parasitic bees,” Jessica says. “Although they do visit flowers for nectar — they still need that sugar for energy to fuel their flight — they’re not spending most of their time foraging because they’re not providing for their young. So what they mostly do is hang around nesting areas.”
Nesting areas could be bare ground with bee nests in it or dead wood with bee holes in it. “They’ll just fly slowly around those nest entrances, looking for a sign that this is a nest that’s ready to enter and lay an egg in.”
Parasitic bee species tend not to be as hairy as many bees are because parasitic bees tend not to have pollen-carrying hairs.
Why It’s Easy to Love Bees
“They’re so beautiful. They’re so diverse,” Jessica says of bees. “They have such interesting behaviors, and they’re a bit bigger than the flies I was working on as an undergrad — big enough that you can, to some extent, identify them in the field and watch individuals go about their lives without having to kill them and put them under a microscope to see who they are.”
Jessica is struck by how bees are like Swiss Army Knives.
“All of their legs have all these different little appendages on them,” she says. “So ground-nesting bees have these little sort of kneecaps and a little plate at the tip of their abdomen. And they apparently use these plates — the kneecaps and this plate at the tip of the abdomen — for sort of tamping down the surface of the brood cells that they dig underground.”
On the front of their bodies, bees have hairs and other bits and pieces for extracting pollen and nectar for flowers. “That’s the stuff that you really can’t see until you get them under a microscope,” she notes.
When structures exist on a male bee but not a female bee, it’s safe to assume the structures exist for reproductive purposes, such as grasping a mate. For example, in some leafcutter bee species, the males have enlarged front tarsi, which Jessica explains are like bees’ hands. “It’s almost like they’ve got these big paws, they’re sort of flattened and elongated. And those are used in mating where the male actually covers the eyes of the female during copulation.”
Pollen-carrying hairs also help to tell bee species apart.
“Solitary and other wild bees will typically carry pollen in a brush of hairs on the underside of the abdomen or on their hind legs, and for bee species that collect pollen from certain types of plants that have unusually large pollen grains, those pollen-carrying hairs will be more widely spaced than in bees that use smaller pollen grains,” Jessica says.
Mouthparts vary in length. “Bees that are visiting flowers with very long nectar tubes will have more elongated mouthparts, and that’s something again, you can see more readily under a microscope,” Jessica notes.
“The diversity never ceases to amaze me,” she adds.
A female ground-nesting solitary bee (Colletes) at her nest entrance.
(Photo Credit: Jessica Forrest)
How Climate Change Is Affecting Native Bees and Phenology
Jessica notes that climate change has diverse impacts on various aspects of organisms. Warmer temperatures have effects on plants’ and animals’ physiology that researchers are continuing to study.
“Experimental work with climate change is quite challenging, but we have learned some things,” she says.
Bees are sensitive to climate change due to how climate change influences phenology — how seasonal and climate variations impact the life cycles of plants and animals. This includes the timing of when plants are flowering and when bees are coming out.
“I was interested in this idea that climate change might be shifting the phenology of different species at different rates, and in particular, shifting plant flowering differently than bee activity, because that would have obvious implications for pollination for bee population persistence,” Jessica says.
When she started her Ph.D. work in 2006, people were just starting to talk about the idea. Since then, she and others have done quite a bit of work on the topic.
“What we often see is that plants are more responsive to temperature variation than insects in terms of their timing,” Jessica says.
What does that mean for plant pollination and the survival of bees? Lots of people have been looking for changes, but there is not a ton of evidence that changes are occurring, she says. However, in one particular case in Japan, it was found that when an early-flowering, spring-blooming plant in the woodlands there blooms really early, it is mistimed with when bees emerge. “There is this danger of mismatch,” Jessica says.
The plants are pollinated less frequently, and the bees don’t have that food source available by the time they come out after overwintering.
The good news in that study is that there is no evidence of the situation getting worse over time.
For plants that typically flower later in spring, blooming a few days or a couple of weeks early is not a big risk because there will still be pollinators around.
In Jessica’s own work in Colorado for about a decade now, she has investigated the effects of mismatched timing on specialist bees that use only one kind of plant for pollen.
“You would expect that specialists would be extremely vulnerable to mismatch, and so I really did expect to see some indication of an effect and just have not seen it,” Jessica says.
She explains that this is due to the broad flowering period of plants. The same flowering plant species may bloom later in a shaded area and sooner in an area that gets full sun. This broadens the period when a specialist bee can find that plant’s pollen.
A stronger influence on bee populations than the presence of flowers is the prevalence of parasites and predators, Jessica points out.
“The thing I’ve learned over the years is to respect the resilience of these little animals,” she says. “… We tend to think about these relationships between bees and plants as these really sort of fragile tightly co-evolved relationships that can’t withstand any change. And that’s, I think, not quite right.”
There is some flexibility built in.
“I don’t want to say they can confront any of the massive threats we’re throwing at them, but I think I have certainly grown in my appreciation of their resilience,” she says.
The nest of a Megachile pugnata bee in a Scopa viewing block.
Photo Credit: Deb Toor
Bee Population Fluctuations
When there are more flowers, bees are able to produce more offspring.
Jessica’s Ph.D. student Lydia Wong has found that in drought years, the number of flowers is reduced and the amount of nectar and pollen that flowers can produce is reduced.
Jessica explains that they can draw this inference because the Rocky Mountain Biological Laboratory in Colorado has been recording the flowering times of individual plants every two to three days throughout the growing season since the early 1970s. The lab as about 30 plots that are each 2 meters square. “They have this incredible data set on flowering phenology and flower number,” she says.
Studying Bee Populations with Trap Nests
Jessica studies bee populations by using trap nests, which are blocks of wood with holes drilled in them. The solitary cavity-nesting bees that she focuses on find these holes to be appealing nesting sites.
“What we can do with those blocks is line each hole with a paper straw,” she explains. “We can then extract a paper straw, we can look at what’s going on in there. So we can count how many brood cells or how many individual potential offspring the bee is rearing in there. We can sample the pollen from the nest, but we also then have sort of a fixed address for each individual bee — like we know where she lives.”
Researchers apply individual paint marks to each bee so they will know when an individual bee finishes a nest and starts a new one. “That’s how we’re able to document lifetime reproductive output for each individual bee. It’s given us kind of a unique dataset because it’s otherwise pretty hard to follow wild insects in the field.”
These traps are similar to bee hotels that gardeners use to provide habitat for nesting bees.
Trap nests used by the Forrest Lab for studying cavity-nesting bees in Colorado. (Photo Credit: Jessica Forrest)
Bee Hotels
Some poorly designed, mass-produced bee hotels have led to bee hotels getting a bad name. A bee hotel with a whole lot of holes of the same size attracts a population of one kind of bee or wasp, attracting parasites that affect that particular species.
“To the extent that those bee hotels draw in parasites, they’re really not helping the bee populations in the long run,” Jessica says.
Jessica has her own home bee hotels because she loves watching bees do their thing. But her bee hotels have few holes, and the holes of various sizes so the hotels won’t to attract a lot of parasites.
“It’s a pretty common phenomenon not just in bees, but if you have large numbers of something in one small area, it’s going to tend to attract parasites and allow parasites to spread from one nest to another,” she says.
A well-designed bee hotel can be helpful, but it won’t be make or break for bee populations. Jessica says bee hotels might increase the bee population a little bit locally. Still, she doesn’t harbor the illusion that more people putting bee hotels in their gardens will solve pollinator decline.
Some bee hotels have a plexiglass pane to view inside solitary bee nests without disturbing them.
“It’s fascinating,” Jessica says. “We’ve seen so many people just kind of have their minds blown by seeing the beautiful structures that mother bees and even wasps can build and the care that they put into providing for their young. It’s really quite remarkable, and it’s something that you just don’t have a window into otherwise.”
A Scopa bee home. It is designed with fewer cavities than a mass-produced bee hotel, and various size cavities for a diversity of species. The presence of too many bees of one species in one habitat encourages the spread of parasites.
(Photo Credit: Ryan Brideau)
I hope you enjoyed learning about native bees with Jessica Forrest. If you haven’t listened to the podcast yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Do you promote native bees in your garden? Let us know how in the comments below.
Links & Resources
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Episode 023: Attracting and Protecting Pollinators with Eric Mader
Episode 232: Ecological Horticulture at Brooklyn Bridge Park, With Rebecca McMackin, Part I
Episode 261: All About Native Bees, with Heather Holm
Episode 316: Celebrate Pollinator Week with Pollinator Partnership
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