Sand flies are tiny insects, often called biting midges or “no-see-ums.” Female sand flies bite because they require a blood meal for egg development, which introduces a risk to human health. Their intensely itchy bites cause discomfort, but their ability to transmit pathogens makes prevention an important health strategy. Effective protection requires a multi-layered approach combining topical products, physical barriers, and environmental control.
Personal Topical Protection
The most immediate defense against sand fly bites is applying approved chemical repellents to exposed skin. Four active ingredients are widely recognized as effective: DEET, Picaridin, IR3535, and Oil of Lemon Eucalyptus (OLE), which contains para-menthane-3,8-diol (PMD). The duration of protection varies significantly based on the concentration and product formulation.
Primary Repellents
DEET (N,N-diethyl-meta-toluamide) is highly effective; concentrations between 19% and 30% are often recommended for high-risk areas. Picaridin, a synthetic compound, is considered equally effective to DEET in similar concentrations. Picaridin is often preferred because it is odorless and less likely to damage plastics or synthetic fabrics. Repellents containing IR3535 have also demonstrated strong effectiveness against sand flies, sometimes offering longer protection than DEET.
Proper application is as important as the choice of chemical. The repellent should be evenly applied only to exposed skin, avoiding cuts, wounds, or irritated areas. Take care to keep the product away from the eyes and mouth. When applying to the face, spray the product onto your hands first and then gently rub it onto the skin.
Use on Children
When protecting children, selecting a lower concentration, such as 10% to 15% DEET or Picaridin, is recommended. Products up to 30% DEET are safe for babies over two months old. Never apply repellent to a child’s hands, as they frequently put their hands in their mouths and eyes. OLE/PMD products should only be used on children who are three years old or older.
Physical Barriers and Clothing Strategies
Physical barriers provide a chemical-free layer of protection and are a foundational part of sand fly prevention. Wearing appropriate clothing creates a simple shield between the insect and your skin. Loose-fitting, long-sleeved shirts and long pants are recommended, since the loose fabric makes it harder for the sand fly to bite through to the skin.
Choosing light-colored clothing is advisable, as sand flies are drawn to dark colors, body heat, and carbon dioxide. For sleeping or covering infants and strollers, fine-mesh netting is necessary because the flies are minute. A mesh size of 500 holes per square inch is required to physically prevent sand flies and other tiny insects from passing through.
Permethrin Treatment
Treating clothing and gear with the insecticide permethrin provides a strong physical defense. Permethrin is a synthetic derivative that works by repelling and killing insects that contact the fabric. The chemical bonds to the fibers and remains effective through several weeks or washes, typically lasting for six washings or six weeks.
Apply permethrin only to outer clothing, such as shirts, pants, and socks, and not to base layers. Application must be done in a well-ventilated area. Once the treated clothing is completely dry, the insecticide is odorless and safe for humans and pets, though wet permethrin is harmful to cats. Pre-treated clothing is available and may offer protection lasting for up to 70 washings.
Environmental and Area Control
Limiting sand fly contact also involves modifying your environment and daily habits to reduce their presence. Sand flies are most active during the cooler hours of the day, specifically from dusk to dawn. Avoiding outdoor activities during this peak biting period can significantly lower your risk of bites. They are weak fliers and tend to stay close to the ground.
Sand flies do not breed in standing water. Their larval stages develop in habitats that provide moisture, shade, and decaying organic matter.
These breeding sites include:
- Moist soil
- Leaf litter
- Animal burrows
- Tree holes
- Cracks in stone walls
Regularly removing organic waste, cleaning up leaf piles, and minimizing damp areas near the home eliminates potential breeding grounds.
Structural protection is a simple yet effective measure for indoor spaces, particularly where sand flies are a known problem. Standard window screens often have mesh too large to block the minute size of a sand fly. To keep the insects out, a tighter weave known as “no-see-um screen” or a 20×20 mesh is needed.
For area control, residual insecticide spraying on indoor walls and surfaces can temporarily reduce the number of adult sand flies resting inside dwellings. However, large-scale control efforts targeting the flies’ hidden breeding sites are often challenging and unsustainable. The most effective approach is to combine these environmental modifications with the personal protection strategies to create a comprehensive defense against sand fly bites.