Spearmint (Mentha spicata) belongs to the Lamiaceae family, known for strong aromas. Spearmint presents a confusing picture for gardeners, functioning simultaneously as a food source for pollinators and a concentrated source of insect-repelling compounds. Understanding this requires looking at the plant in its natural, low-concentration form versus its extracted, highly concentrated essential oil form.
Spearmint’s Floral Appeal to Foraging Bees
The spearmint plant is a resource for various pollinators, including honey bees and bumble bees. When allowed to flower, it produces dense, clustered spikes of small, often white or pinkish-purple blossoms, easily accessible to short-tongued insects. These flowers bloom primarily from mid-summer into early fall, a period when other prime nectar sources may decline.
Honey bees are frequently observed foraging on spearmint flowers, suggesting the plant’s nectar and pollen are readily available. Spearmint provides a steady supply of nectar, the primary carbohydrate source for a colony. However, compared to specialized crops like clover or buckwheat, the small floral structure means individual bee visits may yield less total volume.
The resources are considered adequate, placing the plant as a reliable secondary forage crop rather than a primary, high-yield source. The constant mid-to-late season bloom provides a necessary flow of nutrition, especially for preparing the colony for winter. High visitation rates are often due to the abundance of flowers and the timing of its bloom during periods of scarcity.
Chemical Composition and Deterrent Properties
The shift from attractor to repellent depends entirely on the concentration of the plant’s volatile organic compounds (VOCs). The characteristic scent of spearmint comes primarily from R-(-)-carvone, a monoterpene that constitutes a large percentage of the plant’s essential oil. In its natural, low-level release from the leaves, this aroma is not considered a deterrent to foraging bees visiting the flowers.
When spearmint is distilled into a concentrated essential oil, however, the carvone content becomes a powerful deterrent and insecticide. This high concentration disrupts the neurological or respiratory systems of many insects, often linked to interference with insect octopamine receptors. The intense, volatile odor overwhelms the chemical signals insects use for navigation and communication, effectively repelling them.
The difference in effect is a matter of scale: the gentle, dispersed scent of a garden plant is far removed from the concentrated vapor of an extracted oil. This high concentration of R-(-)-carvone can be toxic to pests and acts as a strong irritant that insects, including bees, actively avoid. This dual chemical identity explains the plant’s contradictory reputation as both a forage source and an insect control agent.
Applications in Beekeeping and Pest Management
Beekeepers leverage the deterrent properties of spearmint oil derivatives to manage hive health, particularly against the parasitic Varroa destructor mite. The oil is used not as a direct insecticide for the bees, but as a treatment to control pests that threaten the colony. Spearmint oil blends are incorporated into sugar syrup mixtures, such as the commercially available Honey-B-Healthy, which is fed to the bees.
When administered in a controlled manner, the low concentration in the feed helps bees resist pathogens carried by mites and may boost their immune response without harming the adult insects. Other applications involve using spearmint oil in higher concentrations, often combined with compounds like wintergreen or lemongrass oil, to create a fumigant effect inside the hive that is highly noxious to the mites.
The volatile compounds, like carvone, create an environment unpleasant or toxic for the mites, causing them to fall off the bees. Beekeepers must use these essential oil treatments cautiously, as excessive application or high concentrations can disrupt the hive environment and cause stress or behavioral disturbances. This highlights the controlled use of spearmint’s repellent chemistry for targeted pest control.