Castor oil is a thick vegetable oil extracted from the seeds of the Ricinus communis plant, also known as the castor bean. The oil is primarily composed of triglycerides, with a large percentage being the unsaturated fatty acid ricinoleic acid. Does this oil attract or repel the insects and pests that frequent homes and gardens? The answer is nuanced, as castor oil acts differently depending on the pest and the application method.
Is Castor Oil an Attractant for Common Pests
Castor oil is not considered an attractant for biting insects like mosquitoes, fleas, or ticks. These pests locate hosts by detecting volatile organic compounds (VOCs), carbon dioxide, and body heat. Castor oil does not contain the fermentation byproducts, sugars, or pheromones that signal a food source or mate to flying or crawling pests.
The oil’s thick consistency and distinct odor are more likely to deter than attract. While it can be used as a standalone repellent, its effectiveness against biting insects is minor compared to synthesized repellents. Its primary value in pest control lies in its ability to be combined with other, more potent natural ingredients.
Castor Oil’s Role in Topical Insect Repellents
When used on the skin, castor oil functions as a beneficial component in repellent blends. It is frequently employed as a carrier oil in natural insect repellent formulations that rely on active ingredients like citronella, lemongrass, or neem oil. The oil’s high viscosity is helpful in this context.
This thick texture helps slow the evaporation rate of the volatile active ingredients from the skin’s surface. By extending the time the active compounds remain present, castor oil prolongs the repellent’s overall efficacy. Its emollient properties allow it to spread easily and create a thin, consistent barrier on the skin. This physical presence may also help mask human scent cues that insects use for host detection.
Using Castor Oil to Deter Subterranean Pests
A distinct application of castor oil is the humane deterrence of subterranean pests like moles, voles, and gophers. For this purpose, the oil is not used as a topical skin treatment. Instead, it is emulsified with water and a surfactant like dish soap, then saturated into the soil. The mechanism of action here is different from insect repellency.
When applied to the lawn or garden, the oil permeates the soil and affects the tunneling animals’ environment. The strong odor and taste act as an olfactory irritant, which is unpleasant to animals with a developed sense of smell, forcing them to relocate. Castor oil also taints the underground food sources of these pests, such as earthworms and grubs, making them unpalatable. This combination encourages the pests to move their tunneling activity elsewhere, offering a non-lethal method of control.