The bright yellow blooms of the Ranunculus genus, commonly known as buttercups, are a familiar sight, often carpeting fields and lawns in the spring and early summer. While their sunny color might suggest they are a bountiful food source for pollinators, the reality is more complicated. Buttercups are available early in the season, but they are generally not highly favored by most common bee species when other options exist.
Why Buttercups Offer Limited Forage
The primary reasons buttercups are considered poor forage relate to the quality of their floral rewards and the presence of chemical defenses. The nectar produced by Ranunculus species typically contains a low sugar concentration compared to more attractive floral sources. This low energy content makes the flower a less efficient foraging target for bees needing to quickly refuel or sustain a colony.
The pollen itself also presents nutritional challenges. While the open structure of the flower makes the pollen readily accessible, its protein content is relatively low. For example, the crude protein content of Ranunculus pollen has been measured around 14.8%, falling below the 20 to 23% range considered ideal for honey bee colony growth.
Beyond low nutrition, buttercups contain a glycoside called ranunculin, which converts into the mild toxin protoanemonin when the plant tissue is damaged. While this compound is primarily known for causing irritation and toxicity in grazing animals, it can also affect bees.
The protoanemonin may act as a chemical defense, making the forage unpalatable or harmful to certain species. A condition known as “May sickness” has been linked to honey bees consuming large amounts of buttercup pollen when preferred food is scarce. This illness is characterized by symptoms like paralysis and convulsive movements, illustrating the potential danger of relying too heavily on this pollen.
Species-Specific Bee Interactions
Interactions with buttercups vary significantly depending on the type of bee. Honey bees (Apis mellifera) are the most likely to ignore buttercups, largely due to the low nectar quality and the potential for the pollen to be toxic. If high-quality forage like clover or willow is available nearby, honey bees will bypass large patches of buttercups.
However, some native and solitary bees display different behaviors. Certain specialist bees have evolved to utilize Ranunculus as a food source, suggesting an adaptation to the plant’s chemical and nutritional profile. Generalist solitary bee species, like the horned orchard bee (Osmia cornuta), often mix buttercup pollen with other types.
Studies have shown that a pure diet of Ranunculus pollen can be detrimental to the larvae of non-specialist bees, leading to poor development. Female bees mitigate these negative effects by mixing the unfavorable pollen with more nutritious pollen from other plants. This strategy allows generalist bees to exploit a wider range of floral resources when options are limited.
Better Early Season Pollinator Plants
Since buttercups offer limited rewards for many bees, gardeners seeking to support pollinators in early spring should focus on planting species known for high-quality nectar and pollen.
Early Forage Options
One of the earliest and most valuable additions is the crocus, which provides readily available nectar and pollen for newly awakened bees. Similarly, winter aconite and snowdrops are among the first to bloom, offering sustenance when few other sources are available.
Trees and shrubs are often overlooked but provide a massive influx of early-season food. Willows (Salix spp.) are especially valuable, producing abundant, high-quality pollen important for native bees. Another excellent option is borage, an annual herb whose star-shaped blue flowers are rich in nectar.
For groundcover, plants like rockcress produce a dense profusion of blooms. Allowing common plants like dandelions to bloom before mowing also provides a simple, early source of nectar. Prioritizing a diverse mix of these early bloomers ensures a reliable and nutritious food supply for all types of bees.