No-see-ums are minuscule biting insects belonging to the family Ceratopogonidae, often referred to as biting midges or sand flies. These pests are barely visible, typically measuring less than 1/16th of an inch, which accounts for their common name. This article clarifies the activity patterns of no-see-ums, details what draws them to a host, and outlines practical methods for avoiding their painful bites.
Activity Patterns and Peak Biting Hours
No-see-ums are primarily crepuscular, meaning their highest levels of activity occur during the twilight hours of dawn and dusk. This preference for low-light conditions makes the early morning and late evening their peak biting times. They thrive in warm, moist, and still air, making their activity closely tied to temperature, humidity, and wind speed.
Biting activity decreases significantly during the brightest, hottest parts of the day and the darkest hours of the night. However, biting can persist throughout a heavily overcast day or in densely shaded, humid locations where conditions mimic twilight. Because they are weak fliers, even a slight breeze can ground them, making them less of a nuisance on windy days.
The insects are highly dependent on moisture; their larvae develop in damp soil, mud, and decaying vegetation near water sources. Areas with high humidity, calm air, and proximity to these breeding grounds experience the most intense activity during transitional times. This explains why they are frequently encountered in coastal areas or near bodies of water.
Why No-See-Ums Bite and What Attracts Them
Only female no-see-ums require a blood meal for reproduction. This blood provides the necessary protein and nutrients for the female to develop her eggs. Male no-see-ums do not bite; they, along with the females when not seeking blood, feed primarily on plant nectar and juices.
Female midges locate their hosts by detecting metabolic byproducts released into the air. The primary attractant is carbon dioxide (CO2), which is exhaled during breathing, signaling a potential blood source. They also sense body heat and moisture, gravitating toward the thermal signature of mammals.
Other cues, such as lactic acid from perspiration and certain body odors, can also draw the midges toward a host. They are known to swarm aggressively once a host is detected, especially in calm air conditions. This behavior leads to bites often appearing in clusters on exposed skin.
Characteristics of the Bite and Common Reactions
When a female no-see-um bites, she uses specialized, saw-like mandibles to slice into the skin, unlike a mosquito which pierces. This action can cause a sharp, burning sensation. To facilitate feeding, the insect injects saliva containing anticoagulants, which prevents the host’s blood from clotting.
The immune system reacts to the foreign proteins in the midge’s saliva by releasing histamine, triggering an inflammatory response. This results in small, intensely itchy red welts or bumps, often appearing in clusters on areas like the ankles, arms, and neck. For some individuals, the reaction can be more severe, including localized swelling or blisters.
The intense irritation and itching can last for several days, sometimes up to two weeks. Immediate care involves washing the affected area with soap and water. Applying ice to reduce swelling or using over-the-counter anti-itch creams, such as hydrocortisone or those containing antihistamines, can help manage the discomfort.
Effective Strategies for Avoiding No-See-Um Bites
The most direct way to avoid bites is to limit time outdoors during the peak activity hours of dawn and dusk. Since these midges are poor fliers, a simple box fan or ceiling fan can be highly effective in outdoor seating areas. The movement of air prevents the insects from landing and stabilizing to feed.
Physical barriers offer reliable protection, as the midges are unable to bite through clothing. Wearing long-sleeved shirts, pants, and closed shoes significantly reduces exposed skin. For home protection, standard window screens are often inadequate due to the insect’s small size.
To prevent entry indoors, specialized fine-mesh screening with a thread count of 50 or higher is necessary. Repellents containing active ingredients like DEET, Picaridin, or Oil of Lemon Eucalyptus (OLE) are recommended for exposed skin. Apply these products thoroughly before going outside, especially during peak hours.
Controlling the environment around a property also helps reduce populations by eliminating breeding sites. No-see-ums lay eggs in moist soil and standing water, so draining any containers or areas with poor drainage is beneficial. Trimming back dense vegetation reduces the shaded, humid spots where adult midges prefer to rest.