Caterpillars, the larval form of butterflies often have specific dietary requirements for a single plant or a group of plants. Many of the plants used as food by caterpillars are present in our lands that are managed for agricultural purposes. Hay meadows are a good source of host plants for caterpillars and nectaring sites for adult butterflies, especially the grassland species. Since 1980, grassland butterflies in Europe have declined almost 20 percent. Recent studies are correlating butterfly populations with management practices of agricultural areas.
In the past, smaller equipment was used to mow and manage pastures for production of hay and forage. The size of the equipment limited the amount of area that could be cut in a single day or brief interval. This limitation meant that contiguous areas of pasture were often in different stages of regrowth. Larger more efficient equipment can now mow larger contiguous areas of pasture in a brief interval. This changes the landscape and habitat available to butterflies and caterpillars. When pastures are mowed in strips or blocks over a longer interval, the un-mowed sections of pasture can provide sources of nectar for butterflies and displaced from the recently mowed areas. The butterfly population surviving on the remaining nectar sources can lay eggs of caterpillars that can colonize the newly mowed sections as they regrow.
Mowing a large area uniformly can remove too many of the nectar sources needed to support butterfly populations. The butterflies must either relocate to a distant area or starve. This inhibits colonization of the newly mowed areas and leads to a decrease in butterfly populations. These effects are documented in a recent paper in the Journal of Insect Conservation.
One recommendation for enhancing butterfly populations in the managed agro-ecosystem is to stagger mowing to maintain a mosaic landscape. This provides refuges and resources that nurture the butterfly populations and encourage recolonization. For areas that are managed for conservation or aesthetic purposes (such as parks and wildlife areas), mowing in a manner that leaves adequate refuge is essential.