As summer arrives and outdoor activities ramp up, one nuisance that many people want to avoid is flies. These pesky insects can quickly ruin a nice cookout or afternoon lounging. Many people turn to citronella candles, it marketed as a natural repellent, to try keeping flies at bay. Here is the evidence behind citronella candles and their effectiveness against flies.
What is Citronella?
Citronella oil is derived from plants in the Cymbopogon genus, including lemongrass. It has a strong, lemon-like aroma. The oil contains compounds like geraniol, citronellol, citronellal, and geranyl acetate which give it its distinct scent. Citronella oil has been registered as an insect repellent by the Environmental Protection Agency since 1948. As an oil, it is commonly used in lotions, sprays, and candles, it used to ward off mosquitos and other bugs.
Why Citronella is Thought to Repel Flies?
There are a few reasons why citronella is believed to help repel flies:
- Strong smell overpowers attractants. Flies locate food and breeding grounds through scent. Citronella introduces a strong, lemon aroma that can mask scents flies would otherwise hone in on.
- Irritation of olfactory receptors. Compounds in citronella oil may irritate flies’ olfactory receptors, making it harder to catch scents they are drawn to.
- Plant-derived, natural repellent. Citronella comes from natural plant sources, unlike synthetic chemical repellents. Some believe natural repellents are more effective against insects, it safer for use around homes.
What Does the Research Say?
Unfortunately, scientific research on citronella candles provides little evidence that they effectively repel flies:
- Limited radius of effectiveness. Studies have found citronella candles must be within 2-6 feet of a surface to repel mosquitos. Since flies can detect scents from up to 100 feet away, candles may not give off enough aroma to confuse their senses.
- Short-lived protection. Citronella oil volatilizes quickly from candles, it loses potency after just 30 minutes of burning. Flies attracted to an area likely won’t be deterred by such temporary scents. Frequent candle replacement would be required.
- Minimal impact on house flies. Research focused specifically on house flies, one of the most common fly species, found virtually no reduction in number of flies attracted to an area with citronella candles burned versus unscented candles. The aroma seems not to deter these flies at all.
- Mixed results against other fly varieties. Studies looking at other fly species like stable flies and horse flies, it limited to moderate reductions in number attracted when citronella candles are present. Results have been inconsistent across different experiments.
- Issues with concentration. Given citronella’s relatively short radius of effect and quick loss of aroma strength, generating a high enough concentration in outdoor areas to confuse fly senses is difficult.
Tips for Getting the Most from Citronella Candles
While far from a magic solution against flies, there are some tips that may help get slightly better results from citronella candles:
- Place candles within a few feet of gathering areas. This increases the chance flies will have to pass through the aroma to get to you.
- Position citronella candles near food, trash cans, gardens and other fly attractants to mask these scents.
- Look for candles that contain at least 5-10% citronella oil for maximum aroma strength.
- Shelter candles from wind, which can prematurely diffuse scent.
- Replace spent candles frequently, at least every 1-2 hours.
- Supplement candles with other fly control methods like fly paper and screen covers. Don’t rely on candles alone.
While marketed heavily as a natural solution, the science shows citronella has significant limitations whe to repelling flies. At best, strategic candle placement combined with frequent replacement may provide minor control. But for any real reduction in fly numbers, consumers should look to more reliable methods and products not dependent on aroma alone.