As temperatures continue to warm and weather patterns keep shifting, some plants are blooming much sooner than they used to. Certain insects are emerging off of their usual schedules, too. The result? Potentially significant disruptions to the life cycles of some of our most industrious pollinators and a decoupling of critical plant-and-pollinator relationships.
“The plants and the insects are responding to different phenological cues,” says Daniel Herms. Formerly a professor and department chair at The Ohio State University Department of Entomology, Herms presently works as vice president of research and development for the Davey Tree Expert Co. He has been monitoring phenological events—natural occurrences synchronized to the weather and the seasons—for nearly 40 years.
“[Plants and insects] respond to temperature differently,” Herms says. “They’re in different niches, and each niche is being affected differently by climate change.”
Generalists vs. Specialists
In part, that degree of impact depends on the relationships insects have with the plants on which they rely. For instance, moths and butterflies tend to be generalists when it comes to their nectar sources. This makes them less susceptible to missed windows of opportunity with specific flowering plants.
“If they’re mismatched with one nectar plant, well, then they just go over to a different nectar plant,” Herms says. (That said, though, they are much more limited in terms of the host plants on which they’ll lay their eggs.)
Tending to be specialists, solitary bees, bumblebees and other types of wild bees are more vulnerable when critical plants are delayed—or missing altogether. “There have been well-documented phenological mismatches with specialist pollinators and specialized pollinator-plant combinations,” Herms says.
In particular, he points to a Japanese study of Corydalis ambigua, a plant in the poppy family, and its relationship to bumblebees. “The flowering times of the plants were dependent on air temperature, and the emergence of the bees is more dependent on timing of snow melt and snow cover,” Herms says.
During years when spring came early, Corydalis ambigua plants flowered before the first bumblebees emerged. As a result of poor pollination, the plants produced less seed. (This, in turn, could affect the future success of both plant and specialized pollinator.)
On the Move
Another result of warming temperatures, the natural ranges of many pollinating insects are shifting and, sometimes, even shrinking.
“In Europe, there is a bumblebee species [whose] southern range has moved north, but its northern range hasn’t moved north nearly as much,” Herms says. “So, its overall distribution has shrunk in response to climate change.
“That’s generally the mechanism by which insects are spreading north, because they’re surviving where they didn’t used to survive. We’re seeing that with some butterflies, with some bees, and with other insects, including pest species like bark beetles. They’re surviving in areas where the winter used to be too cold.”
Over the last several decades, changes in climate also have contributed to earlier insect emergence overall. So, what happens if a specialist pollinator hatches out before its primary pollination plant is available? Or if an insect moves out of the natural range of the plants it needs in order to survive? “Because they can get up and fly, insects move faster than plants in response to the temperature and they can find themselves in areas where their host plants are fewer,” Herms says.
Researchers are still trying to identify the phenological and distributional mismatches taking place and determine what effects such mismatches may have not just on insect populations but also on the plants they pollinate. “Are [plants] having reduced seed set?” Herms asks. “Is there reduced reproduction of plant populations? That’s even less well-documented.”
As a prime example of a disrupted or mismatched species pairing, Herms points to changes in the distribution of agave plants and the resulting effects on their primary pollinators. In this case, it’s the Mexican long-nosed bat.
“Studies show that as the climate warms, the distribution of the agave plant—the suitable habitat for it—is going to shrink dramatically, which threatens this bat with extinction,” he says. “Those kind of things I think we can say are likely to happen in the future, even if the effects are not readily apparent right now.”
While none of us can singlehandedly solve the climate crisis, there is actually a lot we can do to mitigate its effects on pollinators. Job one is increasing the amount of habitat they have access to.
“We know that habitat loss is a major driver of wildlife decline,” says Matthew Shepherd, director of outreach and education for the Xerces Society for Invertebrate Conservation. “If we’re creating as much habitat as we can—putting it in our gardens, in our parks—then we’re making our built landscapes better.”
As for insect pollinators on the go as a result of climate change? “By creating more places they can live, we’re giving them more opportunities to move with fewer barriers to them. They can hopscotch from one patch of habitat to another.”
For his part, Herms replaced about 10,000 square feet of lawn with a native wildflower meadow. “It is a pretty good chunk of habitat, and then we also added larval host plants for caterpillars,” he says. “These backyard habitats are becoming increasingly important—especially in suburban/urban areas where the individual gardener can have a big impact on the biodiversity in a neighborhood.”
Want to create your own pollinator paradise? Aim to have a little something in bloom year-round. Depending on your location, that may mean adding early- and late-flowering bulbs to your landscape. Including a variety of trees or shrubs in addition to large stands of perennial flowers can also make a difference. That way, Herms says, “There’s always something to increase the connections in the food web so that, when the pollinators do emerge—and if they emerge early—there’s something for them. And, if they’re around late, there’s still something for them.”
When considering what to plant, you can’t go wrong with species which are native to your area. Since they’re adapted to your local growing conditions, native plants require little maintenance once they’re established. “There are a number of studies out now that show that native plants have a greater number of benefits for native insects,” Shepherd says. “It’s not just the bees drinking the nectar. It’s also the caterpillars and the other insects that are out there. Native plants are typically better for your native insects.”
If you look for native plant varieties at your local nursery or garden center rather than starting your own from seed, ask the right questions before you buy. “It’s good to think about and ask retailers, ‘What has this plant been treated with?’” Shepherd says. “It’s worth considering how that plant was grown before it got to the shelf in your garden center—particularly with systemic pesticides because these are absorbed into the plant’s tissue.”
“A systemic pesticide could be applied weeks or even months before it gets to your garden and yet it’s still carrying that insecticide,” he says. “And you may be a sustainable gardener who says, ‘I’m not going to use pesticides,’ but you just inadvertently brought that insecticide into your garden.”
To protect your new habitat and the insect pollinators it will attract, choose native plants that have been grown without pesticides.
Planting nectar- and pollen-rich native plants is a great start, but it’s only part of the solution. “If all we’re doing is putting plants in, then we’re only feeding the adult bees and not providing them with a place where they can rear their young,” Shepherd says. “We need to support the entire life cycle.”
If you live in the countryside, you might be able to get away with leaving some dead or hollow trees in place, as these make excellent nest sites for insect pollinators. But if you are in an urban or suburban setting, you can always put out some bee blocks—also known as bee hotels—instead. “If you are putting up a block, you want to have a range of hole sizes or, ideally, a number of different blocks with different hole sizes,” Shepherd says.
Just as you’d clean out a birdhouse annually, any bee blocks you put up will also need some TLC. “Make sure that you keep your bee boxes clean,” Shepherd says. “Hopefully, they get occupied in that first year, and a year on from then, the bees will emerge.”
At that point, you can discard the used block and replace it with a new one or remove the used block, clean it out thoroughly, and reinstall it. Aside from putting out bee hotels so that solitary bees have somewhere safe to overwinter, Herms leaves his spent flower stalks intact. “There are bees and other insects that overwinter inside them,” he says.
“We can create habitat and then protect and conserve it,” Herms says. “I think gardeners and farmers are perfectly positioned to contribute to helping with this problem by increasing their biodiversity overall.
This article originally appeared in the May/June 2023 issue of Hobby Farms magazine.