When it comes to bees, everyone’s familiar with the iconic honeybee, but what many don’t realize is that honeybees are not native to North America. The 4,000 or so native bee species in the United States behave much differently than honeybee colonies and are generally not well understood. To educate us on the diversity of native bees, pollinator conservationist and author Heather Holm joins me on the podcast this week.
Heather is the author of “Bees: An Identification and Native Plant Forage Guide” and an expert on the mutually beneficial relationship between native plants and native pollinators. Her first book is “Pollinators of Native Plants: Attract, Observe and Identify Pollinators and Beneficial Insects with Native Plants” and her most recent is “Wasps: Their Biology, Diversity, and Role as Beneficial Insects and Pollinators of Native Plants,” a National Indie Excellence Award Winner and a natural follow-up to her earlier work.
The depth of Heather’s books blows me away. The information is so thorough and the photography is excellent. Heather has previously been a guest on the podcast to discuss wasps and pollinators of native plants, and I just had to have her back to discuss bees.
We tend to be less afraid of bees than we are of wasps, which all get a bad rap due to a few aggressive species. And while we all know the honeybee, that’s just the tip of the iceberg. In fact, of all the types of bees that are out there in the world, honeybees are the minority.
“People base their model of how bees nest and behave on that one species, the honeybee,” Heather points out. The honeybee we know in North America is Apis mellifera, the western honeybee or European honeybee, and it was introduced to North America. It is a highly social species that often nests in managed hives kept by beekeepers.
Our native and wild bee species behave much differently than honeybees. For the most part, native bees have solitary nests and they are active for only a short period of time during the growing season. “That makes my job hard because native bees are just so different,” Heather says of explaining native bee behaviors. “So it’s hard for people to understand what they’re actually doing day to day and what their life’s mission may be.”
Before proceeding any further with our discussion on native bees I want to take a moment to remind you that I have a new book coming out in September, and it’s available for pre-order now. The title is “The Vegetable Gardening Book: Your complete guide to growing an edible organic garden from seed to harvest,” and I’m very excited for you to read it. It’s chock full of insider tips and new-to-you information that will help you step up your gardening game and tackle challenges.
The Difference Between Bees and Wasps
The main thing separating bees from wasps is their diet. Bees are the descendants of some types of wasps, but bees have essentially become vegetarian as an evolutionary response to the availability of flowering plants and plant-based food sources.
Bees are hairier than wasps, giving them the capacity to move pollen around efficiently. Bees derive all of their nutrients from plant sources, namely pollen and nectar. That makes them herbivores, or phytophages. Meanwhile, wasps are carnivorous.
Heather notes that by the end of their lives, bees may have lost all their hair, making identification difficult.
In bees’ diets, pollen is the primary source of proteins and fats. Pollen is essentially the male reproductive gametes of a flower.
Nectar is usually secreted from nectaries somewhere on a plant — typically in the flowers but other places as well in certain plant species. Nectar is bees’ main source of carbohydrates and can also contain free aminoacids for additional nutritional resources.
Some unusual and rare native bee species collect floral oil to provide to their offspring and to make nest lining. Floral oil is typically found in plants that are nectar-less. Rather than nectaries, they have glands that produce oil. Bees come along, brush that oil off the plants and collect it on their forelegs to take it back to their nests. Native loosestrifes (Lysimachia) are an example of flowers that have floral oil rather than nectar.
How Bees Get Difficult-to-Access Pollen
Some flowers contain pollen that bees can’t get to easily. Many native bee species are able to access that pollen using sonication, aka buzz pollination.
Flowers typically shed pollen from the exterior of their anthers. Certain plants have inside-out anthers, so the only way the pollen can get out is through pores or small valves.
“Then a native bee comes along and says, ‘How do I get this pollen that I want?’” Heather explains. “And they’ve developed this mechanism, sonication, which is essentially grasping hold of those reproductive parts and then temporarily decoupling their wings from their flight muscles and then vibrating their flight muscle cells at a really high frequency.”
That buzzing shakes the pollen out of those pores or valves.
“It’s this really amazing and effective way for them to like buzz out a whole bunch of pollen in a single visit,” Heather says. “So from an efficiency standpoint, the bees are probably pretty pleased with themselves.”
It’s audible to humans when bumblebees practice sonication because it is at a low frequency. When smaller bees, such as sweat bees, do buzz pollination, the frequency is often too high for us to hear it.
How Flowers Attract Bees
Through their evolutionary relationship with bees, different flowers have different ways of attracting bees. Flowers use both visual and scent-based “advertisements” and even electrostatic charges to bring bees to them.
Some flowers have spots or stripes called “nectar guides” that show bees where to find nectar and pollen. And though most insects are red blind, they can see ultraviolet markings on flowers that humans can’t see.
Regarding electrostatic charge, bees usually build up a positive charge and they can sense the difference between the plant and themselves. If a flower has a low charge, the bees know it has been visited recently and will have less nectar available.
Some flowers will change color after they have been visited by a bee. Bees will see that a flower’s color has changed and skip it in favor of a different flower that is still loaded with resources.
Heather compares these advertisements to the signs in grocery stores that let us know what we can find in each aisle: “If they didn’t have the aisle that has crackers and cereal labeled, then we’d be going around the store 8 million times trying to find the crackers in cereal.”
Bees, butterflies and other flower-visiting insects will also leave behind their own scent marks on flowers to indicate that those flowers have already been visited.
Some bee species are generalists that are not picky about their food sources while other bee species are specialists that only collect a certain type of pollen from a single plant genus. Bees that specialize to some degree are called “oligolectic,” and generalist bees are called “polylectic.”
“Monolectic” bees are strict specialists that only take pollen from one species of plant. A “narrow oligolectic” bee only collects pollen from a single plant genus. Then there are bees that collect from a single plant family, and even “eclectic oligolectic” bees that collect from more than one plant family but have diets that are still narrow enough to be considered oligolectic.
Bumblebees make up a bee genus that is considered polylectic, though Heather notes that when looking at individual bumblebee species, their diet preferences are narrower. Factors such as tongue size influence what their diets can be.
Choosing Plants to Benefit Native Bees
If you want to help out native bees, planting native plants will get you off to a good start. You can’t go wrong planting goldenrod and asters in the Eastern United States because they support generalists and a number of specialists as well, Heather points out.
Heather says diversity is always the basic rule because different plants will provide different resources to various pollinating insects. For example, a nectar-less plant may be a good source of pollen, but bees still need nectar-providing plants around.
Planting the specific plants that specialist bee species rely on can attract those bee species to your garden, but not in all cases. Heather explains that some ground-nesting bees require bare sand to nest in, so unless they have a suitable nesting site near their food sources, you may not get them to come to your yard.
In most of the eastern U.S. states, between 20% and 40% of the native bees are specialists. In the Southeast, the southern blueberry bee specializes on blueberry bushes and redbud flowers.
The problem with non-native plants is that they did not co-evolve with our native bees and are not great sources of food for them. In the case of specialist bee species, non-native plants likely serve no purpose at all.
The problem with cultivars (plants developed through selected breeding) is that they may have different color flowers plus harder-to-reach pollen and nectar. They may be more attractive to humans, but bees won’t see them that way.
“Something that may be more vibrant or attractive to us may, in turn, be sort of the opposite effect for some of these insect pollinators,” Heather says.
Identifying Bees vs. Wasps vs. Flies
Lots of flying insects are yellow and black striped, and that can easily lead to confusion in telling bees apart from wasps and flies, but Heather has a few tips on how to differentiate between them.
Flies are the easiest to tell apart from bees, Heather says. Flies have really short antennae — usually just little stubs — and even the longest fly antennae are still shorter than bee and wasp antennae.
Flies truly have just one pair of wings. Bees and wasps have two pairs of wings, however, they can appear to be a single pair of wings, so it’s not the most obvious sign that you are looking at a wasp or bee rather than a fly.
If you look at the insect’s waist, that is a good indicator. Insects with narrow waists are bees or wasps, while flies have big, “robust” waists, or no waist at all.
Flies have little appendages under their wings called “halteres” that look like knobs. Bees and wasps do not.
Bees and wasps have two sets of eyes: large eyes on the sides of their heads called “compound eyes” and three simple eyes on the tops of their heads. The shape and location of the eyes are an indication of a bee or wasp. On the other hand, flies often have eyes that almost touch at the top of the head.
Not all bees are yellow and black. There are metallic green sweat bees, blue orchard mason bees and various other colors of bees.
The Function of Bees’ Simple Eyes
The three simple eyes, or ocelli, that bees (and wasps) have on top of their heads are used for orientation. They work by detecting light.
Consider that 90% of bees are solitary species. The female bees leave their nests multiple times a day to collect pollen and nectar, and they need to find their way back. Those simple eyes help with orienting to the sun. Every time they leave the next they perform an orientation flight so they will know how to return. This starts by hovering above the nest and them flying in widening figure 8 patterns.
For seeing objects in front of them, bees use their compound eyes.
The Life Cycle of Bees
Bees have four distinct life stages: egg, larva, pupa, adult.
Bees and other insects in the order Hymenoptera have haplodiploidy sex determination. After the females mate with a male, the females store the sperm in a special organ. When the females lay eggs, they use that stored sperm to fertilize some eggs that will become females. The unfertilized eggs will develop into males.
The female eggs are generally laid deeper in a social bee nest than the male eggs. The males are more expendable so they get less protection.
During most of a bee’s life, it is in the larval or pupal stage. The adult stage is relatively short. The female adults live maybe four or five weeks as they forage and prepare nests while the male adults live just one or two weeks, just long enough to mate.
Larvae have five growth stages as they munch on pollen and nectar. They then spin a silken cocoon when ready to pupate. Through the pupation process, they develop further and finally emerge as an adult.
Many solitary native bees produce one generation per year. (In North America, 96 percent of bee species are solitary.) During the growing season, the males emerge first from their nests, and then the females follow. This is called a “protandrous emergence.” This happens because the males are not given as much food as the females, so they go through their food stores faster and emerge sooner.
The males fly back and forth over and over again waiting for females. This is called “patrolling.” They are singularly focused and rarely visit plants for food and energy.
Social species, such as bumblebees and some sweat bees, have a life cycle that is a little different. They produce reproductive females in late summer or autumn. Those females mate before they go into hibernation so they are the only surviving part of that bee group after winter.
Solitary, Semi-social and Social
A social bee nest is defined by multiple generations in the same nest, with a queen and her offspring living together, and a cooperative division of labor, working together toward the common goal of producing more bees. This includes honey bee nests and bumblebee nests.
A semi-social nest has maybe two primary egg-laying queens, living mostly with females and cooperatively rearing offspring.
Some solitary bees make their nests near other nests, and some even share a nesting burrow, but they don’t work cooperatively. Communal nests are ground nests shared by two or more females, but each works individually to provision its own brood cells.
Threats to Native Bees
Habitat loss is the biggest and most obvious threat to native bees. Flowerless landscapes and built environments do not leave good habitat for bees.
Pesticides are extremely impactful to bees and other pollinating insects, Heather adds.
A threat people are less aware of is introduced pathogens. Non-native species introduce pathogens that our native species have not evolved defenses to. Those introduced species also compete with our native bees for resources.
Climate change is the big question mark, Heather says. If host plants bloom earlier than they once had and there is a mix-match between the bloom time and the emergence of its specialist pollinator, there can be impacts that we have not realized yet.
“The ‘glass is half full’ part is that it’s quite easy to create thriving bee habitat,” Heather says. Start with finding straight species (rather than cultivars) of native plants to grow in your garden. Plant a diversity of plants with a variety of flowers colors and forms, and ensure there are some plants blooming continuously through the growing season for a 24/7 flower buffet. And don’t clean up as much: bumblebees like it messy. Standing stems and the duff layer provide overwintering habitat for many beneficial insect species.
I hope you enjoyed my conversation with Heather Holm. If you haven’t listened yet, you can do so now by clicking the Play button on the green bar near the top of this post.
What native bees visit your garden? Let us know your results and experience in the comments below.
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“Bees: An Identification and Native Plant Forage Guide” by Heather Holm
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