Chapter 11: Managing for Pollinators

Chapter 11: Managing for Pollinators thompsbb

The Value of Roadsides as Pollinator Habitat

A monarch butterfly perched on a native plant with pink flowers in a roadside.
Sunny public lands that serve as travel corridors between habitats make Iowa roadsides as viable habitats for pollinators. (photo by Roadside Vegetation Manager & Weed Commissioner Chris Henze)

Iowa county and city governments typically want to establish native roadside vegetation to save money on mowing and reduce erosion, weeds, and brush. However, since the 2010s, when news of declining pollinator populations worldwide became widespread, many conservationists and members of the public have become interested in the additional value of native roadside vegetation as a bee and butterfly habitat.

Rights-of-way are seen to have potential as prime habitat for pollinators because they serve as travel corridors between other pollinator habitats and are in sunny locations in which many bees and butterflies prefer to forage. Some people are naturally concerned that encouraging bees and butterflies to forage in roadside habitat will result in many of these pollinators being killed by vehicle collisions. However, several studies have indicated that the pollinators using roadsides far exceed the numbers killed on roads and that there is a net benefit to providing habitat, especially in landscapes with very little native vegetation. High-quality habitats may reduce the number of times bees and butterflies need to cross the road in search of nectar plants or nesting habitats, reducing collision mortality. 

A group of monarchs sits on a native plant with purple flowers.
Iowa roadsides fall within the eastern monarch flyway route for monarch butterflies migrating between Canada and Mexico.

Roadsides also represent a large amount of public land in the United States that could be revegetated with native plants to provide pollinator habitat. This is especially true in Iowa, where road rights-of-way comprise 60% of public land. The viability of monarch butterfly habitat in Iowa is of national importance to conservation efforts because it is one of the few states entirely within the eastern monarch flyway, a major migration route for monarch butterflies between Canada and Mexico.

In 2015, the White House released the National Strategy to Promote the Health of Honey Bees and Other Pollinators, which included a directive to increase roadside pollinator habitat. Later that year, the Fixing America’s Surface Transportation Act (FAST Act) included a provision encouraging pollinator habitat along roadsides. These federal actions have resulted in more efforts to restore habitat for pollinators at the state and local levels. For example, the Iowa Monarch Conservation Consortium’s Conservation Strategy for the Eastern Monarch Butterfly (Danaus plexippus), approved in 2018, identified rights-of-way as a priority area in which monarch habitat planting and preservation efforts should be focused within Iowa. The consortium encouraged the planting of milkweed for monarch caterpillars and nectar plants for adult monarchs in order to increase monarch populations.

A bee hovers over a native plant with pink flowers.
In addition to its direct benefits, an IRVM approach with native vegetation provides a habitat for bees and butterflies.

Pollinator-Friendly Management Practices

Pollinator-Friendly Management Practices thompsbb

Timing of Mowing

Mowing can negatively impact pollinators by reducing floral resources and host plants, which are specific plant species that a given insect species is adapted to for food, shelter, or reproduction. For example, it is well known that monarch butterflies only lay their eggs on milkweed plants, though adult monarchs will forage on many plant species. 

Mowing can also disturb or kill nesting pollinators or pollinators in early developmental stages, such as larvae and pupae that cannot escape during mowing.

Best practices for mowing that support pollinators include:

  • Mowing only in clear zones, which are roadsides clear of objects, where vehicles that have left the roadway can traverse safely.
  • For narrower roads with less traffic, maintain narrower clear zones compared to wider, more trafficked roads.
  • Outside of clear zones, mow roadsides only very early and/or late in the growing season; summer mowing causes a lot of pollinator mortality.
  • When possible, leave perennial shrubs and standing woody stems as habitat for nesting bees.

Herbicide Application

A brown common wood nymph butterfly perched on a native plant with white flowers.
Thoughtful and strategic use of herbicides can protect habitats for pollinators such as the common wood nymph butterfly. (photo by Story County Conservation Vegetation Management Biologist Ty Hamiel)

Herbicide spraying may hurt pollinators by killing or harming eggs, larvae, and adult pollinators. Sublethal effects are non-lethal effects and may include weakening of the immune system, disrupted foraging and navigation behaviors, impaired reproduction, and shortened lifespan. Spraying can also reduce the availability of floral resources and host plants that pollinators depend on.

Best herbicide application practices for supporting pollinators include:

  • Use targeted spraying of weeds rather than blanket spraying to reduce the area affected by the herbicide.
  • Spray early in the growing season, before plants start flowering.
  • Avoid spraying when weeds or nearby plants are flowering.
  • Spray on days with little wind that can cause the herbicide to drift onto desirable plants.
  • Limit herbicide use altogether to address noxious weeds and other high-priority plants to remove.
  • Do not spray insecticides.

Planting Native Vegetation to Attract Pollinators

Best native vegetation planting practices for attracting and supporting pollinators include:

  • Do not plant in medians, which increases the risk of pollinator mortality from collisions with vehicles.
  • Plant diverse mixtures of native forbs and grasses. A general recommendation is to have three forb species that bloom early in the season, three that bloom in the middle of the season, and three that bloom later in the season, so there are flowering resources throughout the season.
  • Remember that a balance with roughly 50% of the mix consisting of grasses and 50% consisting of forbs (by weight of the seeds) helps pollinators. Grasses help reduce the spread of weeds within the habitat, ensure there is enough fuel for a prescribed burn, and ensure there are some host plants for caterpillar larvae that depend on grasses rather than flowers.
  • For more information on flowering plants that are especially attractive to pollinators, check with a reputable native seed nursery or the additional resources listed below.

Additional Resources for Management of Roadside Pollinator Habitat

Additional Resources for Management of Roadside Pollinator Habitat thompsbb

Resources for Landowners and Homeowners Interested in Pollinator Habitat

Resources for Landowners and Homeowners Interested in Pollinator Habitat thompsbb
A monarch perched on a purple rough blazing star flower.
Rough blazing star is a perennial wildflower found in many roadsides with native vegetation that attracts monarch butterflies and other pollinators.

You may encounter residents who want to learn about planting pollinator habitat on their property. The following resources may be of interest to them.

Planning, Designing, Implementing, and Maintaining 

Sourcing Materials 

Funding

Books