Butterflies and diurnal moths along road verges: Does road type affect diversity and abundance?

Roadsides form potential habitats for several grassland species adapted to regular mowing management. We studied the communities of butterflies and day-active moths in 51 sites along the verges of the three road types, i.e., highways, urban roads and rural roads. Despite different traffic densities and widths of the road and verge, the groups were rather similar with regard to soil properties, vegetation structure and mowing intensity. The species richness and total abundance of butterflies (53 species, 5964 individuals) and diurnal moths (46 species, 4626 individuals) were also rather similar in each road type, although a preference for wider verges was observed. Butterfly diversity increased (but not significantly) from the verges of narrow rural roads to wider highways. The highest numbers of meadow species were recorded along highways and the total abundance, especially of diurnal moths, decreased in accordance with the road size. High nectar abundance was the most important factor increasing the numbers of meadow butterflies along road verges, while meadow moths were mostly favoured by shelter provided by tall vegetation. Verges surrounded by cultivated fields were generally related to low numbers of both Lepidoptera groups, whereas adjacent forests increased the total number of all species and favoured several butterflies inhabiting forest edges. The adjacent environment inflicted compositional differences on the Lepidoptera fauna of the three road types. The results indicate that road verges should be considered an important reserve for species dependent on semi-natural grasslands in Finland. A growing interest in accommodating current roadside management for conserving biodiversity is likely to benefit Lepidoptera communities in the verge habitats.