Narrow strips of flowering plants along road edges can support high butterfly diversity, a recent study from Singapore has found.
In late 2023, researchers surveyed 101 road verges — strips of green planted along the side of roads — across the tropical city-state of Singapore, recording 56 species of butterflies feeding on nectar from 96 flowering plant species a total of 1,320 times.
“The most surprising result was seeing how effective even narrow and artificially planted road verges can be in supporting butterfly communities when managed well,” co-authors Tharaka S. Priyadarshana and Eleanor M. Slade, from Nanyang Technological University (NTU) in Singapore, told Mongabay in a joint email.
All but six of the 96 plant species the butterflies visited were nonnative, the study found.
The authors said this suggests that in tropical cities, where flowering and butterfly activity occur year-round, roadside green spaces can serve as “meaningful habitat” for butterflies even if planted with nonnative species.
Many cities regularly cut roadside plants for “aesthetic appeal” and better driver visibility, the researchers say. However, the study found that verges with higher diversity of flowering plants that were cut less frequently and had varying plant heights supported more butterfly diversity than those with “uniform, flat vegetation.”
The authors told Mongabay the flower-rich, less frequently cut verges offer “a cost-effective and space-efficient way to support urban pollinators without the need to have very wide strips of vegetation.”
Not surprisingly, the researchers found that butterfly diversity within the road verges decreased as traffic density and vehicle speeds increased. “[W]hile reducing speed limits may not always be feasible, promoting slower traffic in residential areas and integrating biodiversity-friendly road verge designs can help mitigate the impact of traffic while also improving pedestrian safety,” Priyadarshana and Slade told Mongabay.
The researchers also found that larger green spaces around verges positively influenced butterflies.
“Connecting small linear habitats like road verges at the local scale to larger green spaces such as parks, gardens, or natural remnants at the landscape scale is crucial,” Priyadarshana and Slade said. They added that the “broader network of greenery” provides vital supply of nectar and host plants for butterfly larvae, and creates “mini-environments conducive to butterflies by reducing the harsh impact of weather conditions.”
The authors said their study addresses a research gap since most papers on road verge habitats are from temperate regions, while theirs examined a rapidly urbanizing tropical city. Singapore lost nearly all its primary forests by the turn of the 20th century, but greening efforts since the 1960s have resulted in about 50% of Singapore’s land now being vegetated, mainly as urban parks and secondary forests. “Singapore, which has adopted a vision to become ‘A City in Nature’ by integrating green infrastructure into urban planning, serves as a valuable model for other tropical cities,” the authors said.
Banner image of a striped albatross butterfly (Appias libythea) on a red leea plant (Leea rubra), courtesy of NTU Singapore.
