1. Thank you for downloading this slide set on North Carolina native bees.
Informal talking points and explanations are included in the notes section beneath each slide. To see these notes in Microsoft Powerpoint, select the “view” tab, then click the “normal” button.
All images in this slide show are used under one of the following conditions:
Licensed under a Creative Commons license that requires photographer attribution and allows noncommercial use only
Used with express permission of the photographers, again with attribution and for educational use only
In the public domain
For images downloaded from the Internet, links to original sources (typically including licensing and permissions) are provided in the notes under each slide.
Except for public domain images, photographer names are included with the images on the slides. (Some public domain images also include a credit.)
Slides prepared by Elsa Youngsteadt, NCSU Entomology, July 2016 (updated October 2018) Contact:

2. Biology, Diversity, and Conservation
NC Native Bees
Biology, Diversity, and Conservation

3. Biology, Diversity, and Conservation
NC Native Bees
Biology, Diversity, and Conservation
BACKGROUND
Why bees matter
Bee diversity and biology
HOW CAN WE HELP?
Habitat requirements—Nesting
Dietary requirements—Flowers

4. Bees are essential
87% of flowering plants, and 75% of crop plants, need animal pollinators to reproduce and bear seeds or fruit
Bee pollination accounts for about 3-8% of our food and the majority of vitamins A, C, and E in our diet
Breakfast with bees
Breakfast without bees
Many fruits, nuts, and berries would be lost from our diets without bee pollination. As illustrated in the photographs, grains (and animal products that depend on grains) would generally remain, but we would lose important nutrient sources.
References:
Aizen, M., et al Annals of Botany 103: 1579–1588.
Ollerton, J., et al Oikos 120: 321–326.
Klein, A.-M., et al Proc. R. Soc. B Biol. 274:
Eilers, E. J., et al PLOS ONE 6:e21363 Smith, M. R., et al The Lancet
Note: We often hear that we can thank a pollinator for “one in three bites of food.” While it’s true that about 1/3 of our yield comes from crops that do benefit from pollination (see Klein et al. 2007), many of these would produce some yield even in the absence of pollinators. The total, direct reduction in yield would be only about 3-8% (see Aizen et al. 2009). On the other hand, this 3-8% figure does not account for indirect effects—e.g., effects on milk via cows that eat alfalfa grown from seed that depends on bee pollination. These numbers are harder to come by.
Photos: Laura Russo

5. Native bees enhance honey bee pollination
Managed honey bees do about 80% of crop pollination
Native bees and other animals do the rest
Enhance yield even when honey bees are present
Insurance against honey bee losses
References:
Garibaldi, L. A., et al Science. 339:
Honey bee hives. Photo: David Tarpy

6. Diversity Images: Sam Droege, USGS, public domain
A key to native bees’ essential role in managed and natural ecosystems is their diversity. Because there are so many kinds, each of which does things a little differently, they are together more effective pollinators than any one generalist species like honey bees.

7. Diversity World 20,000 North America 4,000 NC 500+ Triangle area 100+
Just how diverse are they? These numbers indicate the approximate number of bee species in each area.
World
20,000
North America
4,000
NC 500+
Triangle area 100+
Single yard 70+

8. What defines a bee? E. Youngsteadt Guido Bohne E. Youngsteadt
That diversity encompasses a huge variety of forms, from wasp-like cuckoo bees (top left; Nomada) to bulky carpenter bees (bottom left; Xylocopa virginica). What makes them all bees? (And not wasps?) Bees are essentially vegetarian wasps; they are a branch in the wasp family tree. But whereas the closely related wasps hunt prey (caterpillars, spiders, other invertebrates) to feed their larvae, bees collect pollen (top right; bee larva on a pollen provision). Related to this, bees always have branched hairs somewhere on their bodies, and wasps don’t (bottom right, image of magnified bee hairs).
Source of downloaded image:
E. Youngsteadt
E. Youngsteadt

9. Basic life cycle Larva Egg Pupa Nesting Adult Foraging Guido Bohne
tpjunier
H. Ikerd
Egg
Pupa
To conserve bees, it’s helpful to understand their life cycle and biology. We most often see bees when they’re foraging (bottom center; female Megachile leafcutting bee), collecting nectar and pollen to feed themselves and their larvae. If we’re lucky, we also see evidence of nesting, the other main activity of adult bees (bottom left; female Megachile leafcutting bee). The development of immature bees is hidden from view, underground or inside logs or hollow stems. This starts with an egg, which the female bee lays inside a constructed chamber packed with the nectar and pollen she collected (top left; Osmia mason bee egg). The egg hatches into a larva that eats that provision (top center, Osmia mason bee larva). When it’s done feeding, it pupates (top right, Megachile leafcutting bee). Finally, it emerges as an adult bee (bottom right, male Megachile leafcutting bee).
Note: All pictured bees are in the family Megachilidae, but they are not all the same species.
Sources of downloaded images:
Bernhard Plank
Nigel Jones
Nesting
Adult
Gideon Pisanty
Foraging

10. Variations on the basic life cycle
Guido Bohne
Larva
tpjunier
H. Ikerd
Egg
Social organization
Nesting location
Diet
Pupa
Although all bees go through these stages, they do so differently. We’ll look at a few major variations in bee life cycles that have implications for their habitat requirements. First, we’ll look at social organization: who actually does the work of laying eggs and gathering food.
Bernhard Plank
Nigel Jones
Nesting
Adult
Gideon Pisanty
Foraging

11. Solitary (~90% of species)
E. Youngsteadt
Matt Bertone
In most species, there is no social organization! For about 90% of bee species, it’s every bee for herself: Each individual female constructs her own nest, collects all the pollen and nectar her offspring need to develop from egg to adult, and lays her own eggs. Mining bees (left and top) and mason bees (bottom right) are just a couple of examples of the many species that are solitary. You may see their nests in groups—they can nest very near each other, as in these Andrena mining bee nests (top left)—but they are not collaborating. Another way of thinking about it is that there are no “queens” or “workers” in these species; each female carries out both functions herself.
Source of downloaded image:
Osmia texana
E. Youngsteadt
Sam Droege

12. Social (~10% of species) Steve Nanz E. Youngsteadt
The main alternative to the solitary lifestyle is a social one. This means that bees live together in a shared nest and only one female lays eggs. Most of her daughters become workers that help her feed the young and maintain the nest. Honey bees are an extreme example of this. Our most social native bees are bumble bees. (The photo at left shows a bumble bee colony—see additional details below.) Some sweat bees are also social. One example is the tiny sweat bee Lasioglossum imitatum (top right, each bee is 3-5 mm long). Some of our green metallic bees also form colonies (bottom right, Augochlorella aurata). Unlike honey bees, these colonies last one season only; they don’t survive over the winter and into subsequent years.
More about bumble bees:
Colonies may include dozens to thousands of workers; hundreds are fairly typical.
Queens found new colonies in the spring; for the first several weeks of colony founding, they do everything on their own just like solitary bees. Then, when their first eggs develop into adults, those bees become workers. From then on, the queen stays in the nest and lays eggs, while the workers forage and help care for the developing brood. By the end of the season, the colony produces a new generation of queens and males. They leave the colony and mate; males die, and queens hibernate until the following spring.
You can see several interesting things in the image on this slide, including:
Stored nectar is visible in the open nectar pots (this is just enough for a few rainy days—no extra for winter or for sharing with humans)
Developing larvae are hidden inside the closed, orange wax blobs on the left
Pupae are hidden inside the lighter colored wax pots on the right.
Source of downloaded images:
E. Youngsteadt

13. Parasitic Dick Belgers Elsa Youngsteadt
There’s a third way that bees go about feeding and housing their offspring: They enter an existing nest, built by a different species, and lay their eggs there. Their larvae then eat the pollen that was collected by the other species, generally killing the original resident egg or larva. These bees are often known as cuckoo bees. They are physically incapable of collecting pollen themselves; they must “steal” from other bees.
A few examples of cuckoo bees are shown here:
Top left: Cuckoo leafcutting bee (Coelioxys, pronounced see-lee-OX-iss) lays eggs in nests of non-parasitic leafcutting bees.
Bottom left: Holcopasites calliopsidis lays eggs in nests of the small, common ground nesting bee Calliopsis andreniformis.
Right: Nomad bees (Nomada) often lay eggs in nests of mining bees (Andrena). You can see them in action in the spring, if you watch a nesting aggregation of mining bees.
Source of downloaded images:
Elsa Youngsteadt

14. Variations on the basic life cycle
Guido Bohne
Larva
tpjunier
H. Ikerd
Egg
Social organization
Nesting location
Diet
Pupa
Another major variation in bee life cycles is in where they make their nests.
Bernhard Plank
Nigel Jones
Nesting
Adult
Gideon Pisanty
Foraging

15. Ground (~70% of species) Elsa Youngsteadt Jason Gibbs
The majority of bees—about 70% of species—dig tunnels in the ground to make their nests. Aboveground, all you see is something that looks like a little ant mound, or maybe a little turret. Belowground, tunnels lead to nesting chambers, sometimes a foot deep.
Left: In this photo, a sweat bee (Halictus ligatus) ground nest has been partly opened. You can see a bee peeking out on the left, and on the right is one of her pollen balls with an egg.
Top right: A spring nesting aggregation of mining bees (Andrena) and cellophane bees (Colletes) can superficially resemble anthills
Bottom right: A cellophane bee (Colletes) at its nest entrance.
Jason Gibbs
Margarita López Uribe

16. Cavity (~30% of species) Gideon Pisanty Scott Famous Jeff Brown
The rest of the species—about 30%--nest in some sort of above-ground cavity. There is a lot of variation within this category. For example:
Top left: Mason bees and leafcutting bees use empty beetle tunnels in firm wood and other, similar cavities. This is a nesting block that has been provided for orchard mason bees, Osmia lignaria. Completed nests are capped with mud. Although these bees are nesting in close proximity, their lifestyle is solitary. There is one bee per tunnel.
Bottom left: The solitary green sweat bee Augochlora aurata nests in cavities in soft, rotting wood. In this nest, the oldest offspring are on the right and the youngest (still pupae) are on the left.
Bottom right: The large carpenter bee Xylocopa virginica is the only one of our native bees that chews its own tunnels in sound wood. (A common misconception is that they eat the wood; in fact, they just “drill” it out to make a nesting space, leaving piles of sawdust beneath.)
Top right: Small carpenter bees (Ceratina) are close cousins of large carpenter bees, but they don’t “drill” wood. Instead, they remove pith from hollow twigs to make nesting space.
Source of downloaded images:
Jeff Brown
Elsa Youngsteadt

17. Nesting in the garden: Exposed, undisturbed soil
Marian Dörk
Given what we now know about native bee nesting biology, how can we provide habitat for them in yards and gardens? For ground-nesting bees, there is no one-size-fits-all solution. In general, their soil requirements are not well known, but some prefer sandy soil, others clay; some prefer slopes or embankments, others will nest on flat ground. Dense vegetation, landscape fabric, and bark/wood mulch are generally deterrent. So rather than install something new in your landscape, one strategy is to be vigilant—watch for where little ground nests show up and then keep those kinds of places safe; don’t bury them in mulch or landscape cloth. Keep an eye on any bare soil, even the little bare borders between grass and planting beds. Another idea—if you do want to install something purpose-made—is to construct something like an herb spiral that provides assorted soil environments: north-facing, south-facing, moister, drier, deeper, shallower. There aren’t data to show that this particularly attracts ground-nesting bees, but, in principle, it should offer soil conditions that appeal to different species.
Source of downloaded image:
South-facing slopes often preferred Soil type sandy to clay (species vary)
Wood mulch is a deterrent A mulch of decorative river stones is favored by some species

18. Nesting in the garden: Hollow stems
Tim Waters
Cavity nesters are easier to provide for. Some, such as small carpenter bees, dig the pith out of hollow stems, so we can plant things that provide that habitat. These include plants such as sumac (top left), raspberries (bottom right), blackberries, and fennel. Many leafcutting bees and mason bees naturally nest in beetle exit holes in firm wood; we can simulate that habitat using hollow reeds or bamboo bundled together in a so-called “bee hotel” (top right).
One caution about bee hotels is that sanitation is important; it’s not a good idea to just put one up and forget about it. The high concentration of nests can accumulate parasites and pathogens, so the tubes need to be replaced every 2-3 years to keep things healthy. One way of doing this is to take them down in the fall, store them in a cold, safe place over the winter, and set them out in a dark box in the spring. Put a hole in the box so emerging bees can exit; but the box should not attract bees to build new nests.
Finally, note that different species prefer different diameter cavities. If you have reeds or holes of assorted sizes, your hotel will be occupied by various species—likely including some wasps. However, the wasps that occupy these nests are solitary and are not typically aggressive at all.
Sources of downloaded images:
Elderberry, boxelder, dogwood, blackberries, raspberries, sumac
For “bee hotels,” hygiene is crucial
Even cavity nesters need soil
Andrew Fogg

19. Nesting in the garden: Mixed cavities
Another example of a bee hotel/insect hotel that provides a variety of cavity sizes and textures.
Adam Dale

20. Nesting in the garden: Bumble bees
Elsa Youngsteadt
Finally, a word about bumble bees (top left). They don’t fit neatly into the ground-nesting or cavity-nesting category. They tend to nest in places where other things have previously nested; many use old rodent burrows and mouse nests. They may show up in wall voids, attics, and bird houses that haven’t been cleaned out after the birds move on (right). If you have bird houses, keep an eye out for bumble bees; you can also plant long clumping grasses that tend to provide protected nesting areas around the base of the clump.
Sources of downloaded images:
(public domain)
(public domain)

21. Variations on the basic life cycle
Guido Bohne
Larva
tpjunier
H. Ikerd
Egg
Social organization
Nesting location
Diet
Pupa
Another major variation in bee life cycles is in their diets.
Bernhard Plank
Nigel Jones
Nesting
Adult
Gideon Pisanty
Foraging

22. Dietary specialization
Specialist
Generalist
All adult bees drink nectar, and female bees mix nectar and pollen (or sometimes floral oils) that their larvae will eat. Bees differ in which flowers they use, especially as pollen sources.
Some species are extremely specialized, using pollen from very few kinds of plants. An example of this is the squash bee (Peponapis pruinosa; left), which uses pollen only from plants in the genus Cucurbita (squash, pumpkins, zucchini, gourds). Limited studies with larvae of specialist bees have shown that at least some of them can’t develop, or develop poorly, on the pollen of the wrong plant.
At the other end of the spectrum are extreme generalists who use (and require) many kinds of plants. Bumble bees (right) are an example of this: Because they are active for many months, they must use many kinds of plants as different species come into bloom. They also sense the nutritional value of different pollens and try to optimize their diets.
“Specialist” and “generalist” aren’t clean categories; it’s more of a continuum. Many bees are somewhere in the middle; for example, blue orchard bees (Osmia lignaria, center) have a strong preference for fruit trees, such as apples and peaches, but have also been found to collect pollen from at least a dozen other plant families.
Source of downloaded image:
Susan Ellis
E. Youngsteadt
E. Youngsteadt

23. Specialist bees need specific pollen
Marc Ryckaert
When planning a garden to feed both specialist and generalist bees, it’s helpful to know what plants the specialists use. This is illustrated with this pie chart, which summarizes the diets of 85 species of specialist bees in the mid-Atlantic region. It shows what proportion of those bees are specialized on each plant family. The most popular plant family for specialists is the Asteraceae—things like sunflowers, joe-pye weed, asters, and goldenrod. The Ericaceae, especially blueberries, also host a number of specialist bees. Also willows, and so on.
Reference (includes specific host plants by genus):
Sources of downloaded images:
E. Youngsteadt
André Karwath
Jacopo Werther

24. Feeding bees in your garden
So, when it comes down to it, how do you decide what to plant? Diversity is key, for both generalists and specialists. Debbie Roos’ slides (also available for download) provide more specific tips on plant choice; for now, we’ll leave it here. As we convert our yards and gardens in to bee-friendly habitat, we want places like the one on the left to start looking a little bit more like the one on the right.
Sources of downloaded images
(USDA copyright free)
(USFWS)