Oil of citronella comes from several species of grasses. The substance has been used for more than 50 years as an insect repellent in the U.S. Oil of citronella products are sold as repellent candles, skin lotions and sprays. Citronella candles are only for outdoor use. Neem oil is extracted from the evergreen Azadirachta indica, native to India. The plant's leaves and seeds contain sallanin, a compound with insect repelling properties. Pennyroyal oil is toxic if ingested, but is part of many consumers product to apply on the skin.
Some plants that produce insect-repellent substances also can have a fragrance that repeals them. Marigolds and the mint pennyroyal are two examples that are easy to grow in your garden. Although citronella grasses can release fragrances that biting flies do not like, these tropical plants can grow taller than 6 feet, and are not likely to fit in many people's gardens.
When camping or going outside for long periods of time, avoid insect bites by wearing long sleeves and pants tied at ankle level. You should also tuck your shirt into your pants. Some clothes are made with special fabrics that receive a coating of pyrethrum, a natural repellent from daisies of the genus chrysanthemum. However, before buying any clothing check the label, because many manufacturers use a laboratory-synthesized equivalent called permethrin.
Although it can sound too unconventional to some people, having bats nearby can help to repel biting flies and mosquitoes. Despite their bad press, bats are important pollinators, and many species of bats feed on insects, such as mosquitoes and biting flies. The little brown bat is common in North America, and feeds mainly on insects. Building or buying a bat house to put near your home is the best way of attracting bats.