The culinary herb basil (Ocimum basilicum) is often recommended for garden planting because its potent aroma is widely believed to deter insects. This leads to the expectation that the plant should actively repel ants. However, gardeners frequently observe ants crawling on their basil plants, creating confusion about the herb’s true effect. Basil possesses strong defensive properties, but the presence of ants is usually due to a secondary, indirect attraction.
Basil’s Natural Effect on Ants
Basil’s characteristic scent results from its production of volatile organic compounds (VOCs), which function as natural insect defenses. These compounds are concentrated in the plant’s essential oils and include chemicals such as linalool, methyl chavicol, and eugenol. When released, these molecules create an olfactory environment disruptive to many insects, including various ant species.
The primary mechanism of repulsion involves interfering with an ant’s chemical communication and navigation systems. Ants rely heavily on pheromone trails to find food and guide colony members. The dense aroma of basil’s VOCs can effectively mask or overwhelm these delicate pheromone signals, causing disarray among foraging ants. For example, linalool has been shown to exhibit repellent properties against certain insects. Consequently, the basil plant itself is generally unattractive to ants looking for a direct food source.
Why Ants Might Still Appear Near Basil
If basil is naturally repellent, the presence of ants indicates a different food source has overridden the plant’s defenses. Ants are not attracted to the basil leaves but rather to honeydew, a sweet, sticky substance. Honeydew is the sugary waste product excreted by sap-sucking insect pests, such as aphids, mealybugs, or scale insects.
These pests feed by extracting phloem sap, which is rich in sugars. The excess sugar is expelled as honeydew, which ants actively seek out. Ants frequently develop a symbiotic relationship with these pests, often called “farming.” The ants protect the pests from predators in exchange for a continuous supply of the sweet excretion. Therefore, an ant infestation on basil is a clear indication of a secondary pest problem that needs to be addressed.
Safe Methods for Ant Management
The most effective strategy for managing ants on basil is to eliminate the underlying pest infestation providing the honeydew reward. A strong jet of water from a hose can physically dislodge soft-bodied pests and ants from the stems and leaves. This physical removal should be repeated every few days to manage the pest population.
Using Insecticidal Soap
Another method involves using insecticidal soap, which is safe for use on food crops. A mild solution of water mixed with a few drops of unscented liquid dish soap or Castile soap can be sprayed directly onto the affected areas. The soap solution works by breaking down the pests’ outer protective layer, causing dehydration, and helps wash away the sticky honeydew residue.
Creating Physical Barriers
To prevent ants from climbing back onto the plant, apply a ring of diatomaceous earth to the soil surface around the base. This fine, naturally occurring powder is harmless to humans and pets. It acts as a desiccant and abrasive to the ants’ exoskeletons. By removing the honeydew source and establishing simple physical controls, the ants will quickly lose their reason to frequent the basil plant.