No-see-ums, also known as biting midges or sand flies, belong to the insect family Ceratopogonidae. These tiny insects measure less than three millimeters, making them nearly invisible and allowing them to pass easily through standard window screens. Due to their aggressive biting habits and ability to evade typical barriers, many people seek natural alternatives to chemical repellents. Plant-based solutions deter these pests by utilizing their aversion to specific aromatic compounds.
Identifying Effective Repellent Plants
A number of common garden plants produce volatile chemicals that effectively repel biting midges. Citronella Grass (Cymbopogon nardus) is known for its insect-deterring properties, primarily due to its high concentration of citronellal and citronellol. Crushed leaves release a potent, citrus-like aroma that confuses the midges. Closely related Lemon Grass (Cymbopogon citratus) also contains these compounds, offering similar repellent effects.
Rosemary (Salvia rosmarinus) contains aromatic oils unappealing to many biting insects, which deter pests while adding a pleasant scent to outdoor areas. Basil (Ocimum basilicum), another culinary herb, possesses several volatile compounds, including citronellal, estragole, and limonene. The plant’s strong scent is often sufficient to keep insects at a distance even without crushing the leaves. Marigolds are also effective, containing compounds like pyrethrum that naturally irritate and repel no-see-ums.
How Plant Compounds Deter Biting Midges
The repellent action of these plants is rooted in the release of volatile organic compounds (VOCs) that interfere with the midges’ sensory systems. Biting midges are attracted to hosts primarily by the scent of carbon dioxide (CO2) and chemical signals, such as lactic acid, present in human breath and sweat. The aromatic compounds from plants, such as monoterpenes and sesquiterpenes, work by dominating the ambient air.
This concentrated plant fragrance effectively masks the human odors midges rely on to locate a blood meal. The plant chemicals overload the insect’s chemoreceptors, confusing the pests and preventing them from accurately tracking their target. In some cases, the compounds may also be mildly irritating or toxic, causing them to avoid the area where the scent is strong.
Maximizing Repellency Through Strategic Use
Plants should be used strategically beyond simple cultivation in a garden bed. Placing potted repellent plants near high-traffic areas, such as doorways, patios, and outdoor seating arrangements, establishes a barrier of protective fragrance. Brushing past the foliage, especially when plants are placed along pathways, helps bruise the leaves and release a higher concentration of repellent oils into the air.
For a more intense effect, leaves of plants like Lemon Grass, Basil, or Rosemary can be crushed to extract the volatile oils and rubbed directly onto exposed skin. Another method involves boiling the plant material, such as Rosemary sprigs, in water to create an infused spray for skin or clothing. Placing dried or fresh sprigs of Rosemary onto a warm grill or fire releases aromatic smoke that can help clear a small perimeter of pests.