Pollination, Bumble Bees and Gardening for Conservation

The buzzing of a drill driving into dead wood broke through the light chatter of people and birds around us. Julian, a volunteer, was carefully boring holes into a sawed-off section of a tree trunk. Under the instruction of Dr. Adrian Carper, an entomologist with CPW, Julian was busy making homes for insects like mason bees and grass-carrying wasps. “Of our 1,000 species [of bees], probably 300-350 of them are what we call cavity nesters,” said Adrian. “Bees can’t make their own cavities; they actually rely on beetles … larvae eat the dead wood, and then when they emerge, they leave behind this hole — and that’s the only place in the world where [these] bees can nest.” With a normal power tool and presumed yard waste, Julian was creating a potential mason bee apartment complex. For anyone dealing with rotting wood or a looming dead tree on their property, Adrian had some insect-friendly advice: “Chunk it up, put it on the landscape, drill some holes, and you’ve just created bee habitat.” In a pollinator garden, a vertebrate’s trash is an invertebrate’s real estate. 

Volunteers with Wildland Restoration Volunteers (WRV) were gathered at Barr Lake State Park to establish a native pollinator garden. Many might know Barr Lake as a primo spot for birds (visitors with binoculars and Nikons are nearly as numerous as the birds themselves on some days), but this day was about bees. By planting native flowers, grasses and shrubs, all in attendance were giving a leg-up to Colorado’s busiest insects. But CPW’s work with insects goes well beyond individual gardens. 

House Bill 24-1117 gave CPW the authority to study and manage the state’s more neglected plants and animals; as a result, CPW created the Invertebrate and Rare Plant Program, devoted to studying and conserving some of Colorado’s less-appreciated living things and their habitats.

In a way, the definition of “wildlife” has been rewritten. In our minds, wildlife are typically large, elegant mammals that draw crowds to parks and zoos — moose, elk, bears and others dubbed “charismatic megafauna,” the sorts of species that go on the logos of wildlife agencies. The new program’s focus may be on wildlife that’s smaller in size, but much bigger in abundance.

“We went from 960 species that CPW is managing to orders of magnitude more,” said Dr. Hayley Schroeder, who leads the program.  Due to the challenges of studying invertebrates, Hayley and her team have had to develop a fresh approach to species conservation, especially in light of the upcoming State Wildlife Action Plan (SWAP). 

The SWAP is a collaboration of wildlife scientists at CPW that establishes which species are in need of the greatest attention for protection and research, and outlines what conservation actions should be prioritized. All 50 states develop a SWAP every 10 years. SWAPs revisit plans from 10 years before, reevaluate priorities and make a plan for the next decade. A major aspect of the SWAP is identifying Species of Greatest Conservation Need (SGCN), and assigning tiers to each species according to how vulnerable it is.

“For our vertebrates, we’re able to do [a] pretty rigorous evaluation of every species,” said Hayley, as drills continued to buzz in the background. As for invertebrates, “that’s just not possible. … there’s just too many species.”

The Humble Bumble

If darting wasps are like fighter jets, bumble bees are like helicopters, slowly yet efficiently making their way from landing zone to landing zone, i.e., flower to flower. 

Bumble bees are common and well-liked for their teddy-bearish qualities (perhaps “charismatic microfauna” will catch on), but they’re somewhat misunderstood. “People assume that everything that honey bees do, all bees do.” said Hayley. Bees, I soon learned, are up to a lot more than just making honey.

Honey bees live in elaborate, neatly constructed nests that house thousands of individuals, each with a role that they’re physically restricted to. Only the queen in a honey bee hive is capable of reproducing, all workers are female and nonreproductive, “drones” are males that live in the hive and mate with the queen to grow the colony — similar in structure to the colonies of many ant species. 

That’s honey bees, but there’s more than one way to make a hive. Some bees are completely solitary; others, like small carpenter bees, live in social groups with a dominant female, but all individuals are reproductive, and group members cooperatively tend to the nest and larvae.

Bumble bees have their own system. Their hives are much smaller and more roughly constructed than honey bee hives. Inside a hive lives a queen and all of her daughters, over which she has dominance. She secretes a hormone that prevents her daughters from producing eggs; if one does manage to lay eggs, the mother promptly eats them. Each cohort of daughters takes care of the next, bringing back pollen for their larval sisters to eat. Because the nest has more provisioners as time goes on, the daughters get bigger and healthier with each cohort. But the maternal tyrant seals her own fate — the last of her daughters are the biggest and strongest, and don’t need to accept their mother’s terms. If their mother tries to stop them from laying eggs, they may kill her, if she doesn’t die naturally at the end of the season. Either way, the queen’s reign ends, and the next generation is left to hibernate through the winter and start hives of their own next season. While honey bees generally run a well-oiled machine where social roles are biologically fixed, the social lives of female bumble bees are volatile political sagas. “It’s kind of a Game of Thrones situation,” said Adrian. 

Broadly, bumble bees are mountain bees; in fact, they evolved in the Himalayas, a mountain range that spans between Tibet and Nepal. Around 35 million years ago, there must have been a bee with a genetic mutation (a genetic bumble, we might say) that gave it a little extra fuzz that kept a bit more frost off its body, or made it grow to a larger size, allowing it to retain a little more of the heat it produced when buzzing. With its newfound success, that bee had offspring that shared in that success, and the offspring of those offspring did the same, and so on; with each generation, bees in that bloodline grew better and better suited to mountain habitats. Now, thanks to that first strange little bee, we have the genus Bombus — bees with very “bee-ish” stripes and translucent wings but somewhat “bear-ish” bulkiness and hairiness, bumble bees. 

Since that first bumble, these bees have stuck with the mountains, retaining adaptations to cool, high-elevation environments. Across the globe, the number of bumble bee species is highest in subapline (just below the treeline) grasslands with plenty of flowers. Colorado ranks among the bumble hotspots around the world, with 25 species (about half of all the species that occur in North America). While bumble bees are a common sight in the state, several of Colorado’s species are in danger, Hayley and Adrian assured me. 

The western bumble bee, for example, ranges from Alaska to southern California, and extends eastward into Colorado. That’s an impressive range, but it isn’t found in all habitats within that range. “If you start to look more closely at finer scales of its distribution [range], it’s patchy,” said Adrian, the program’s pollinator conservation manager. The western bumble bee is a high-elevation specialist, and a detailed view of its range wouldn’t show a neat, unbroken shape that you might see in a field guide, but a splattered canvas of splotches limited to mountain ranges. Through time, those patches have gotten smaller — as the climate has warmed, western bumble bee populations have moved up in elevation and latitude, following the cold conditions it’s adapted to. 

“Really, it’s those changes in distribution that we’re keying in on to inform our conservation,” added Adrian. 

Because it’s difficult to track individual insects (just try fitting a radio collar on a cuckoo wasp), we have less fine-grained information on bumble bees than we do, say, lynx or elk. Distribution data for a species — which shows where they’re being seen rather than giving specifics on where they go, what they do, etc. — allows conservationists to infer what its most important habitats are and how its population has changed over time. 

To get the best data on bumble bees in preparation for the SWAP, Hayley and Adrian are working with Xerces Society for Invertebrate Conservation. Xerces has data collected by community scientists, nonspecialists who participate in research, who catch bumble bees, put them in a cooler long enough to immobilize them, and then take a picture that can be identified by a bumble bee expert. Most insect research involves lethal capture — often with traps that can be left for long periods, using ethanol to preserve the specimens — but the Xerces program allows for nondestructive sampling. It also collects a lot of data by welcoming anyone who’s interested to join in the fun. 

Earlier I said that today wasn’t about the birds, but the bees; actually, you might say it’s about the birds and the bees (so to speak), and everything in between. The study and conservation of pollinators is about the connections between living things, the threads that run through ecosystems, and the roles that pollinators play, known as ecosystem services.

Conservation ecologists want to maintain functional redundancy in ecosystems. Most plants can be pollinated by more than one kind of pollinator, and most pollinators can pollinate more than one kind of plant, meaning that a given ecosystem service is often being performed by more than one species. Maintaining a diversity of species that provide the same ecosystem service is an insurance policy for an ecosystem, an extra bit of scaffolding to support it; if one bee species, for example, goes into decline, there are many other bees that pollinate the same flower, performing the same service.

Before talking with Hayley and Adrian, I pretty much knew what pollinators did: A butterfly, for example, drinks nectar from a flower, gets some pollen on it and that pollen falls off at the next flower the butterfly visits. At the very basic level, that’s fairly accurate; what surprised me was how many kinds of pollinators, and styles of pollination, there are.

The Pollination Game

It’s not just birds and butterflies that pollinate. Cacao, the plant used to make chocolate, is pollinated by a type of midge. Agave, used to make tequila, completes its life cycle with a bat pollinator. There are mosquito pollinators. Beetles, birds and even some lizards also play a role in pollination.

Pollination is often incidental. When a monarch butterfly drops off a small delivery of pollen, it’s really done so by accident — pollen just happens to get on the wings of the butterfly at one flower and happens to fall off at another. But, it’s a decent deal for both parties: The milkweed gets pollinated, and the monarch gets nectar. Fair’s fair. There’s only a handful of instances, however, of “active pollination” in the world. A female yucca moth shoves pollen down the stigma of a yucca, which leads to the plant’s ovary, with her moth parts, intentionally cultivating it. She then lays her eggs at the base of the ovary so that her larvae can eat the fruit that develops. But if it lays too many, the deal’s off — the yucca plant kills the egg by aborting its developing fruit, leaving the yucca moth’s larvae with no food. 

Many bees are somewhere in between. Look closely (but carefully) at a bumble bee on a flower and you may see neatly stored wads of pollen sticking to its back legs. Unlike many other pollinators that only drink nectar, bumble bees eat pollen. The collections of pollen on their legs are for transport back to the hive and fed to larvae. Digger bees, solitary ground nesters, “buzz pollinate.” The anthers (the pollen-containing parts at the center of a flower) of some nightshade flowers will only release pollen if a bee that buzzes at a specific frequency goes near it. And the buzzing isn’t just the sound of its wings beating; in this case, “buzzing” is when the bee lands on the flower and intentionally rattles its body, no wing movement required but producing a similar sound, to activate the nightshade’s anthers.

Pollination is often a negotiation between the pollinator and the pollinated. The terms are set by evolution, and their life cycles become linked; they coevolve towards an “understanding” with one another.

The following weekend at Lory State Park, net in hand, Adrian stalked another insect in the tall grass. He swung with the precision of a batter following a pitcher’s curveball, snagging the mystery insect and spinning the net to entrap it. Adrian bravely stuck his hand into the net and pulled out a hover fly, a pollinating fly that mimics the black-and-yellow patterns of bees for protection from predators. Though at a distance it was very bee-like, a close-up view showed the rounded, all-eyes head of a fly.

Busy as Bees

The main action that day was the planting of another pollinator garden, this one with vegetation from the three life zones that make up Lory: grasslands, foothills and mountainous areas of the park. A life zone is an area with a distinct combination of moisture levels, elevation, soil type and other features that determine what kinds of plants can grow there. The conditions that make up a life zone are the nonliving raw materials of habitat; a life zone is the starting point before the living things — like plants, pollinators, herbivores and predators — can move in.

“A lot of people think that when we want to help pollinators, we just need to put in flowers; however, the word ‘pollinator’ comes from pollen. Trees, shrubs and flowers produce pollen, and they’re all essential for insects,” said Annemarie Fussell, a WRV training manager, who ran the event. To that end, volunteers, equipped with hori horis (a knife-like digging tool), worked from the morning into the late afternoon transferring plants into the bare plot: grasses like grama (a favorite food of caterpillars), flowers like yarrow and aster (favorites of bees), and conifers like junipers and ponderosa pines (more habitat for insects). 

Demonstration gardens like these serve as a summary of the park, a sampling of the plants and pollinators it contains. “Not everyone coming to this park is going to walk far from the trailhead. Not everyone in this park is going to climb 1,000 feet up into the ponderosa forest,” said Annemarie. “This gives them access to a broader diversity of plants, and shows them how beautiful nature can be, with the hope that they will say, ‘I want this in my yard.’”

For those who are so inspired, getting your own native garden started isn’t too difficult. Many native plants are available at local nurseries (The Colorado State University extension office keeps a list of commonly available natives, sorted by water usage, blooming season, etc.). The Colorado Native Plant Society offers guides, free to download, on what plants will do best in your garden based on the life zone you live in. Xerces provides lists of the best plants for pollinators by region.

Once your garden is established, you generally need to water it regularly in the first year, but after that, it largely takes care of itself. After its first year, Annemarie’s personal native garden was more a way to unwind than a high-maintenance, manicured project. “I water it once a month if we don’t get any measurable rain,” she said. “I watch my neighbors water three to four times a week and mow twice a week and spray chemicals. I don’t do that. I just watch the birds.”

There is a part of me that wants to garden. Really, I want to want to garden. I wish I were the sort of person that was driven to comb through plant lists online and populate my yard with pollen-bearing plants to enrich my local ecosystem — but I’m more of a drone than a worker bee. For those like me — concerned but, for whatever reason, without plans for a personal garden — there’s still a way to help out. 

“Volunteer! Join us to support native plants and pollinators and everything else about the outdoor spaces around us,” said Kevin Pierce, WRV’s Youth, Family and Bilingual Program Coordinator, who ran the Barr Lake event, over email. “Our project calendar offers something for everyone from half-day events near home to weekend long backcountry projects.” Find your planting event here.

By: John Anglin, CPW Communications Specialist