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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - September 2017

September 2017
Issue No:
Vol. 81 No. 2
Publication Number:
Table of Contents

Save The Bees and Butterflies!

by Deirdre Remley and Allison Redmon

By managing roadside vegetation, transportation agencies can help conserve the pollinators that are essential to the production of our food. Without them, we’d starve.


Luis Colon, Arizona DOT

FHWA has developed best management practices and other tools to help transportation agencies identify ways they can integrate pollinator-friendly practices into their programs for managing roadside vegetation such as in this median in Arizona.


Odds are you’ve heard about the disappearing honeybees and butterflies. Indeed, pollinators are in trouble. Wild pollinators such as monarch butterflies, bumblebees, and other native bees are experiencing dramatic declines due to a loss of habitat, disease, parasites, overuse of pesticides, and various other factors.

State and local departments of transportation can help reduce some of these threats, at least along roadsides. To assist with appropriate management approaches, the Federal Highway Administration has developed best practices and other tools to help DOTs identify ways that they can integrate pollinator-friendly practices into their landscape design and their programs for managing roadside vegetation.

“FHWA case studies, handbooks, and other materials not only support the resurgence of pollinators but also reduce roadside operational costs, improve ecological outcomes, and benefit local and regional economies,” says Hari Kalla, acting associate administrator for the Office of Planning, Environment, and Realty.

The Importance of Pollinators

Pollinators are essential to ecosystem health. Pollinators visit flowering plants, shrubs, and trees seeking sustenance in the form of sugary nectar and protein-packed pollen grains. While they forage, they transfer pollen grains between blooms, enabling flowering plants to reproduce. An estimated 85 percent of the world’s flowering plants depend on animals–mostly insects–for pollination. Pollinators sustain wildland plant communities that provide food and shelter for myriad other wildlife.

They are also essential to human well-being. As pollinators decline, so does agricultural production, putting the Nation’s food supply and agricultural economy at risk. More than two-thirds of crop species are dependent on pollinators, including crops that produce fruits, vegetables, spices, nuts, seeds, forage for livestock, and fiber plants such as cotton. From the coffee you drink in the morning to the apple pie you have for dessert, an estimated one in three mouthfuls of food and drink that you consume comes from a pollinator-dependent crop. In fact, the majority of vitamins, minerals, and nutrients we need to maintain our health (such as vitamin C, calcium, and folic acid) come from fruits and vegetables that depend partially or fully on animal pollinators. In the United States, the value of crop pollination by insects is estimated at up to $27 billion.

Most pollinators are insects: bees, wasps, flies, beetles, butterflies, and moths. Hummingbirds also pollinate, as do nectar-feeding bat species. Bees are particularly critical pollinators. Beekeepers manage colonies of domesticated honeybees to provide both pollination and honey. The native bees of the United States–approximately 4,000 species–have very different lifestyles from honeybees; most native bees live in the wild rather than in managed hives. Native bees are excellent pollinators, and many play a critical role in crop pollination, such as the native bees that pollinate alfalfa, an important feed crop for livestock.

Pollinator Species in Decline

Pollinator declines threaten U.S. agriculture and put the health of natural ecosystems at risk. The number of honeybee colonies in the United States has been falling over the past half-century, and beekeepers have experienced record-high average hive losses (about 29percent) annually.

Other North American pollinator species appear to be experiencing similar or even more severe declines than honeybees. At least 25 percent of North America’s bumblebee species have undergone significant and swift declines due to habitat loss, insecticide exposure, and disease. Butterflies have undergone similar declines: 17 percent are at risk of extinction. The eastern population of the iconic monarch butterfly declined by 84 percent between the winter of 1996–1997 and the winter of 2014–2015. Loss of the monarch’s breeding habitat–milkweed–is a significant factor contributing to this decline.

Roadside Vegetation’s Role in Pollinator Conservation

In 2015, in response to evidence of the steep declines in certain pollinator populations, Congress included administrative provisions addressing pollinators along roadsides in section 1415 of Fixing America’s Surface Transportation (FAST) Act. This section directs FHWA to encourage pollinator habitat and forage development on transportation rights-of-way.

Roadside vegetation can offer much-needed habitat for pollinators, providing food, shelter, and connections to other patches of habitat. With millions of acres of rights-of-way overseen by State DOTs, managing roadsides is a significant conservation opportunity.


Photo: Jennifer Hopwood, Xerces
Society for Invertebrate Conservation

Bees like this one pollinate crops while also sustaining wildland plant communities that provide food and shelter for myriad other wildlife.


Roadsides and Pollinators

How are roadsides useful to pollinators? Roadsides offer several ecological benefits for pollinators. The vegetation can provide food, such as native wildflowers, that pollinators rely on as sources of pollen and nectar, and the caterpillar host plants that butterflies and moths need to complete their life cycles. Roadsides also provide breeding or nesting opportunities for pollinators, as well as shelter and overwintering habitat. They help pollinators to move through landscapes by linking fragmented habitats–and the roadsides themselves give refuge to pollinators in otherwise inhospitable landscapes.

What types of roadside management strategies benefit pollinators? Roadsides with abundant and diverse native wildflowers managed with judicious mowing and herbicide use, as well as other management tools, provide the best pollinator habitat. Shrubs and trees are also important components of pollinator habitat when they are compatible with the design of the roadside.

If the amount of roadside wildflowers increases, will the number of pollinators killed on roads increase? Many people are concerned that by increasing the quality of habitat on roadsides, more pollinators will be killed by vehicles. In fact, research indicates that roadsides with high-quality habitat actually reduce pollinator mortality because the insects stay on the roadside instead of leaving to search for flowers.

Do pollinators need native plants on roadsides? Native wildflowers are especially important for pollinators, because most nonnative cultivated flowers have little or no nectar. Native plants support more species and a greater abundance of pollinators than do nonnative plants. Roadsides with native plants are the most valuable to pollinators.


Not all roadsides are equally beneficial to pollinators. Roadsides that are intensively mown, blanket-sprayed with herbicides, or planted with introduced grasses support far fewer species of pollinators and smaller population densities than roadsides managed for native plants.

On large construction projects, landscape design is an opportunity to establish pollinator habitat with native plants adapted to the local area. Most native plants have deep root systems that are excellent for stabilizing soils post-construction and thus achieving important erosion control objectives while creating aesthetically pleasing, low-maintenance roadside landscapes that serve as habitat for pollinators.

Roadsides can offer feeding, breeding, and nesting opportunities for pollinators, and also can aid pollinator migration by linking fragmented habitats and forming habitat corridors. With the right conditions, roadsides can support a diversity of generalist pollinators, including bumblebees, honeybees, butterflies, and hummingbirds, as well as rare species. Roadsides extend through all types of landscapes and can be particularly important sources of habitat in highly altered landscapes such as intensely managed agricultural lands or urban areas.


Jennifer Hopwood, Xerces Society for Invertebrate Conservation

The eastern population of the monarch butterfly, shown here, declined by 84 percent in the past 18 years.


Vegetation management affects how pollinators use roadsides and even influences the number of pollinators killed by vehicles driving nearby. A European research study, “Factors affecting road mortality and the suitability of road verges for butterflies,” published in 2013 in Biological Conservation, found that the frequency of mowing was linked to the proportion of butterflies killed by cars because the insects were forced to disperse to find new habitat after roadsides were mowed. In contrast, mortality was lower where roadsides had more species of plants and higher quality of habitat because butterflies did not have to fly to new areas. By reducing the need for pollinators to disperse elsewhere to find food or nesting sites, high-quality roadside habitat can decrease the numbers of pollinators killed by vehicles.

Roadsides managed with pollinators in mind can achieve the goals of stabilizing roadsides, reducing stormwater pollution, supporting wildlife, and increasing public appreciation of the local landscape.

Roadside Management Strategies

In 2015, FHWA’s Office of Project Development and Environmental Review led an effort to develop best practices for improving pollinator habitat in roadside rights-of-way. The best practices outline how modifications to existing vegetation management practices can provide conservation opportunities to increase pollinator habitat and improve pollinator health.

In February 2015, contractors for FHWA interviewed staff from State DOTs and roadside restoration experts who work with DOTs. The goal was to document existing roadside vegetation management practices and obtain feedback from those professionals about the feasibility of implementing strategies that can benefit pollinators.


Pollinator Partnership

Here, Queen Anne's Lace graces an urban roadside in California. FHWA's pollinator resources outline the cost-saving benefits of activities such as limiting mowing and designing landscapes with native plants that require less costly long-term maintenance.


Adding the pollinator aspect to Florida’s wildflower program, for example, elicited an enthusiastic response from Jeff Caster, a landscape architect with the State’s DOT. He called the pollinator element “very, very significant because, before, [the program] was for enjoyment. Now it has a more serious purpose, more useful, and is perceived as more valuable.”

Subsequently, FHWA published Pollinators and Roadsides: Best Management Practices for Managers and Decision Makers (FHWA-HEP-16-020) and Roadside Best Management Practices that Benefit Pollinators: Handbook for Supporting Pollinators through Roadside Maintenance and Landscape Design (FHWA-HEP-16-059). The best management practices described in these publications can help roadside managers maintain roadside vegetation and design roadside plantings in ways that increase the number and diversity of pollinators, and support pollination services for nearby crops and native plant communities. The strategies, outlined below, can be adapted to a particular region and situation, recognizing that transportation agencies have different resources and constraints.

Protecting and managing remnant habitat and existing stands of native vegetation. Conducting inventories of roadside vegetation to identify existing roadside habitat and weed problems, followed by site-appropriate management plans that maintain plant diversity, will help with managing existing roadside vegetation effectively, while also benefiting pollinators.


Luis Colon, Arizona DOT

FHWA's pollinator-friendly practices are helping DOTs manage their roadside vegetation, as with this right-of-way in Arizona.


Adjusting mowing practices to benefit pollinators. Reduced mowing of the roadside beyond the clear zone can benefit pollinators and help to reduce maintenance costs, and does not need to compromise aesthetics or roadway safety. Transportation agencies also can reduce the frequency of mowing, consider the timing of mowing, and adopt mowing techniques that reduce the effects on pollinators.

The frequency and timing of mowing of the entire roadside right-of-way varies among States and also within some States. In some, mowing takes place in the late spring and early fall; in others, midsummer and early fall. Some roadsides may be mown in certain regions to reduce the fuels that contribute to wildfires. In urban areas, roadsides typically are mown more frequently to accommodate the perceived aesthetic preferences of road users. Some States have mowing exceptions to protect sensitive plants. In addition, in some States, private citizens may mow the roadside adjacent to their property and use the vegetation as hay for animal fodder.


Jennifer Hopwood, Xerces Society for Invertebrate Conservation

Reduced mowing, as shown here Michigan, is a cost-saving strategy, as well as a pollinator-friendly practice.


Generally, it is ideal for pollinators if roadside vegetation is mown no more than twice during the growing season. It is important to time mowing to minimize disruption of the life cycles of rare, endemic, or sensitive and declining species of pollinators. Mowing only once in autumn or after the first frost will benefit a variety of pollinators by allowing flowering plants to bloom uninterrupted throughout the growing season, and will reduce the risk of mortality to larval stages that reside on vegetation.

Reducing the impacts of herbicides on pollinators. DOTs can take a number of steps to reduce the effects of herbicides on pollinators, including using herbicides carefully and efficiently, avoiding damage to nontarget plants, reducing herbicide exposure to pollinators, and communicating with adjacent landowners.

DOTs use herbicides throughout the growing season as needed to control noxious weeds, invasive weeds, and encroaching woody vegetation. Herbicides also are applied in areas that cannot be mown, such as beneath guardrails or on gravel shoulders. Some DOTs time herbicide applications for peak effectiveness against their target weeds. Herbicide use, and the subsequent effects of herbicides on pollinators, can be reduced through the use of selective herbicides, spot-spray applications, and the timing of applications during life stages when the weed is most vulnerable. Training provided to roadside managers about the timing and selection of chemicals for particular weeds, weed identification, and native plant identification also can reduce the amount and frequency of herbicide use.


Idaho DOT

A transportation agency can adjust mowing practices to benefit pollinators by reducing the frequency of mowing, adjusting the timing of mowing, and adopting mowing techniques that reduce impacts on pollinators. Here, a maintenance worker is cutting roadside vegetation in Idaho.


Designing roadside landscapes to benefit pollinators. Landscape designers and engineers can increase the value of roadside plantings for pollinators by including wildflowers, native bunch grasses, shrubs, and trees that provide pollinators with food or shelter, and can select plants for pollinators that do not compromise highway safety.

Adopting proven methods to establish native plants. Native plants can be an effective tool for managing roadside vegetation, providing effective erosion control, buffering against invasive nonnative weeds, adapting to local conditions, requiring fewer labor and material inputs, reflecting a region’s natural heritage, and supporting increased wildlife. Pollinators are more abundant and diverse on roadsides with native plants.

Many States prioritize native plant species for revegetation rather than introduced plant species. Other DOTs use native plants to a lesser degree, mixing nonnative plants and cultivars with native species. Native plants are used most often in rural areas, and ornamental plantings are more common in urban areas.

Native plants on roadsides sometimes face threats from pesticide drift from adjacent land, intentional herbicide use, or excessive mowing or haying from landowners living adjacent to roadside rights-of-way. Success in establishing native plants often depends on planning ahead to select the right species and ensuring that conditions are right for planting. Success also depends on building internal expertise in restoration by learning from other transportation agencies and local experts. When planning revegetation projects, designers can select native species that are adapted for particular site conditions, which will establish more successfully than a general regional mix. Plans that include a diversity of flowering plants with sequential and overlapping bloom times will provide resources for pollinators throughout the growing season.

Raising public awareness. Positive feedback from the public also can increase support within DOTs. Engaging and informing the public can help significantly in building support for a transportation agency’s roadside restoration efforts. Agencies can generate public support for roadside restoration programs by distributing educational information through a number of avenues and producing effective restorations that can serve as examples of success.

Doing It Right

Washington State Department of Transportation (WSDOT). WSDOT has a long history of managing its roadsides for cost efficiency and environmental stewardship. Based on a detailed programmatic environmental impact study that WSDOT conducted in 1993, the agency determined that an integrated vegetation management (IVM) program would be an effective, natural, and self-sustaining approach to maintaining Washington roadways. The State’s IVM methods include biological control, selective use of herbicides, trimming, soil improvements, native plantings, and mowing. Employing IVM is a way to consider different treatments, based on site-specific conditions, and manage over the long term for safety, cost-effectiveness, and improved habitat for native plants and animals, including pollinators. WSDOT maintains annually updated IVM plans for all 7,000 miles (11,265 kilometers) of State highway corridor in Washington.

Texas Department of Transportation (TxDOT). The TxDOT wildflower program began in the 1930s with a simple but important message, “Don’t mow until the wildflowers have gone to seed.” Because TxDOT vegetation managers recognized that native flower species are less costly to maintain, these plants and their associated pollinator habitat have thrived on Texas highway roadsides for decades. More than 5,000 species of wildflowers grow along Texas highways, attracting millions of tourist dollars. TxDOT maintains wildflowers on approximately 800,000 acres (323,748 hectares) of roadside as part of its vegetation management program.


Training management staff. Significant knowledge gaps about managing roadsides as natural resources are evident in some DOTs. Education and training are indispensable if provided by transportation agency personnel and roadside restoration experts, especially in these five areas:

  • Importance of pollinators and their habitat needs
  • Identification of native plants
  • Establishment and management of native plants
  • Lists of ecoregional species of affordable plants that support pollinators
  • Examples of targeted management changes to benefit pollinators

Staff training on how to implement management practices that benefit pollinators, how to incorporate pollinator habitat elements when designing new roadside plantings, and why the practices that are undertaken can make management programs and roadside restoration projects more successful and efficient. Providing staff with training that includes background information is important, as is information about the long-term economic and ecological value of native plants.

Going Forward: Tools Needed for Change

With transportation agencies facing funding challenges and aging infrastructure in need of repair and replacement, finding ways to make pollinator-friendly practices as efficient as possible is an important goal. FHWA’s pollinator resources outline the cost-saving benefits of actions such as reducing mowing and designing landscapes with native plants that require less costly long-term maintenance. FHWA’s partners in the DOTs are the best resource for building a knowledge base of cost-effective management techniques and design successes. FHWA’s efforts will continue to highlight the work that stakeholders do to protect critical pollinator resources that are important to the Nation’s food security, economy, and natural ecosystem processes.

FHWA will update its “Pollinators” Web page regularly, as more is learned about the ways that the agency’s partners are showing their stewardship in protecting pollinators. Please check the site regularly to find the latest state of the practice in protecting, improving, and establishing pollinator-friendly roadside habitat.


North Carolina DOT

Engaging and informing the public can help build public support for a transportation agency's roadside restoration efforts, as this "Pollinator Habitat" sign in North Carolina suggests.


“FHWA continues to support our State and local partners as they explore innovative ways to manage roadside vegetation that benefits pollinators,” says FHWA Acting Executive Director Gloria Shepherd.

Deirdre Remley is an environmental protection specialist in the FHWA Office of Project Development and Environmental Review with 23 years of experience in environmental review. She has worked for the U.S. Forest Service, the National Park Service, the Arizona DOT, universities, and research labs. She has a master’s degree in anthropology from Northern Arizona University.

Allison Redmon has 10 years of experience in communications and transportation. She provides communications support for the Denver Department of Public Works, and previously for the FHWA Office of Planning, Environment, and Realty through the Cadmus Group. She has a master’s degree in transportation policy from George Mason University.

For more information, visit or contact Deirdre Remley at 202–366–0524 or