Morning glories, belonging to the genus Ipomoea, are widely recognized for their colorful, trumpet-shaped blooms. While bees are drawn to the visual cues and potential food reward, the relationship is nuanced. Morning glories are not designed to be primary bee flowers; they evolved specific floral traits that favor other types of pollinators, making them a secondary food source for most bee species.
The Flower’s Designed Pollinators
The morphology of many common morning glory varieties is specialized to accommodate visitors with long mouthparts. The flower’s large, funnel-shaped corolla, a deep, fused petal tube, is an adaptation for non-bee pollinators. For instance, species with vibrant red flowers are adapted to attract hummingbirds. These birds possess long beaks and tongues suited to reach the nectar reserves deep within the floral tube while hovering.
Other varieties, particularly those with white or pale-colored blooms, like the Moonflower (Ipomoea alba), are designed for nocturnal visitors. These flowers open at dusk and emit a strong fragrance to attract hawk moths (sphinx moths), which are long-tongued insects active at night. Moths unroll their long proboscis to sip nectar from the base of the deep tube, facilitating pollination. By focusing the nectar reward deep inside the flower, morning glories ensure that only capable pollinators effectively carry pollen.
Why Morning Glories Are Not Optimized for Bees
The physical and temporal characteristics of the morning glory flower create distinct limitations for the majority of bee species. The most significant constraint is the flower’s brief blooming period. Ipomoea flowers open around sunrise and typically begin to close by midday or early afternoon, especially on sunny days. This narrow window restricts access for bees whose foraging activities peak later in the day.
The deep, tubular structure of the corolla presents a major morphological barrier for most common bees, including honey bees and many bumble bees. Nectar is located at the base of this tube, making it inaccessible to bees with short or medium-length tongues. Bees attempting a legitimate visit must crawl far into the trumpet, which is inefficient. This anatomical mismatch means the flower’s structure does not facilitate efficient resource collection or effective pollination for the bee.
The availability of the pollen reward is also affected by the flower’s structure. While pollen is usually more accessible than nectar, the deep funnel can make it difficult for bees to efficiently brush against the anthers and stigma. Furthermore, the plant often employs self-pollination mechanisms that occur early in the morning as the flower opens. By the time a bee arrives, the flower may have already completed fertilization, making the pollen less necessary for cross-pollination.
When and Which Bees Visit
Despite the structural limitations, bees do visit morning glories, often under specific circumstances or when they possess specialized adaptations. The most significant exception is the Morning Glory Bee (Cemolobus ipomoea), a solitary, native species that specializes almost exclusively on the pollen of certain Ipomoea species. This specialist relationship highlights that some bees have co-evolved to overcome the plant’s defenses by targeting the pollen.
Generalist bees, such as smaller native sweat bees (Halictidae), also opportunistically visit. These visits occur very early in the morning, immediately after the flower unfurls, when the pollen is most abundant and accessible. They may also engage in nectar-robbing, where a short-tongued bee chews a hole in the side of the corolla to bypass the deep tube and access the nectar directly.
Recent studies suggest that some common morning glory populations have been evolving in response to environmental changes. They are producing slightly larger flowers with an increased investment in nectar and pollen. This evolutionary shift may be an adaptation to attract a wider range of pollinators, including generalist bees, syrphid flies, and wasps. While not strictly a bee flower, morning glories can still provide a valuable, brief supply of pollen and nectar for certain bees, especially small native specialists and early-morning foragers.