The Black-Eyed Susan (Rudbeckia hirta) is a familiar North American plant celebrated for its bright, daisy-like yellow-orange petals and dark central cone. This species, which acts as an annual, biennial, or short-lived perennial, is a popular ornamental and a staple in wildflower meadows. Though hardy, it serves as a food source for a variety of animals, from large browsing mammals to minute insect larvae.
Mammalian Consumers of Black-Eyed Susans
Larger herbivores, such as deer and rabbits, occasionally consume Black-Eyed Susans, particularly when preferred forage is unavailable. Deer generally consider the plant unappealing, often rating it as “seldom severely damaged.” The mature foliage’s strong taste and coarse, hairy texture typically deter extensive browsing. However, during periods of scarcity, like drought or harsh winter, deer may target the most vulnerable parts, including new spring growth, tender shoots, and flower buds.
Rabbits pose a more significant threat, especially to young plants. They are attracted to the tender leaves of seedlings and new growth, which lack the full defense of mature foliage. A rabbit’s feeding activity leaves a clean, 45-degree angled cut on the stem, a distinct sign compared to the ragged tear marks left by deer. This early-season consumption can result in moderate to heavy damage to emerging Rudbeckia hirta plants.
Insect Pests and Larval Feeders
A different class of consumers targets the plant at a smaller scale, causing damage through chewing or sap-sucking. Aphids are common pests, using needle-like mouthparts to extract sap from the stems and leaves, which can lead to wilted foliage. They also excrete honeydew, a sticky substance that encourages the growth of black sooty mold.
Other insects and mollusks directly chew the plant tissues. Slugs and snails feed on the foliage, leaving irregular holes, particularly in damp garden environments. Larvae of certain butterflies, such as the Silvery Checkerspot and the Emerald moth, use the Black-Eyed Susan as a host plant. Goldenglow sawfly larvae can also be highly destructive, occasionally defoliating entire plants.
Plant Defenses and Unpalatability
The plant’s robust defense mechanisms limit the animals that frequently feed on Black-Eyed Susans. Both physical and chemical deterrents contribute to its unpalatability. The specific epithet hirta, meaning “hairy,” refers to the dense, stiff hairs, or trichomes, covering the stems and leaves.
These trichomes act as a physical barrier, creating a rough texture difficult for larger mammals to chew and digest. Chemically, the plant produces secondary metabolites, such as sesquiterpene lactones. These compounds impart a strong, bitter taste and are mildly toxic, discouraging most browsing animals.