Midges are tiny flying insects, typically only a few millimeters long, often mistaken for small mosquitoes. While they belong to several families, the biting midges of the genus Culicoides cause the most discomfort for humans and animals. Their attraction is not random but relies on a sophisticated system of chemical, thermal, and environmental cues. These cues guide the female midge in her quest for a blood meal necessary to develop her eggs.
The Primary Attractants: Chemical Signals
The initial and most potent long-range signal that attracts female biting midges to potential hosts is the presence of carbon dioxide (CO2). As mammals exhale, a plume of CO2 is released, which midges can detect from distances up to 200 meters away. This gas acts as a general beacon, signaling the existence of a warm-blooded animal nearby. The insect uses specialized receptors on its antennae to follow this concentration gradient back to its source.
Once a midge is within close range of a host, a complex blend of volatile organic compounds becomes the primary attractant. One of the most significant is lactic acid, produced in human sweat and released through the skin. This compound, along with others like acetone, 1-octen-3-ol (octenol), and various phenolic compounds, is sensed by the midge. These chemicals are often products of the bacteria that live on the host’s skin, which combine to create a unique scent profile.
Body heat and the resulting temperature gradient also play a part in the final approach to the host. While chemical odors bring the midge close, the warmth emanating from the skin helps the insect pinpoint the precise location for landing and biting. Biting midges prefer a warmer microclimate, consistent with the heat emitted by a large mammal. Furthermore, pheromones released by a female that has successfully found a blood meal can trigger a mass attack by other females, leading to rapid swarming behavior.
Environmental Draw: Moisture and Habitat
Midges are highly dependent on specific environmental conditions for survival and reproduction, which dictates where they are most commonly found. High humidity and minimal air movement are preferred conditions, as they are poor fliers and thrive in moist air. Wind speeds above 7 miles per hour can effectively ground them, making still, humid air their preferred state for activity.
The presence of standing or slow-moving water and damp soil is a powerful attractant because these are the required breeding grounds. Female midges lay their eggs in saturated areas, such as the mud/sand/silt exposed in intertidal zones, or in damp, organically rich substrates like decaying leaf litter, marshes, and wetlands. Even poorly drained lawns, clogged gutters, or small puddles can provide the necessary moisture for their larval development.
The timing of midge activity is closely tied to light intensity. Biting midges are generally crepuscular, meaning they are most active around dawn and dusk when light levels are reduced. During the day, they seek sheltered areas, such as dense vegetation or long grass, to avoid direct sunlight and desiccation. This preference for shaded, still, and moist microclimates explains why they are frequently encountered in boggy ground and undergrowth.
Addressing Common Beliefs About Attraction
Beyond chemical and environmental cues, midges are attracted by visual stimuli, specifically motion and color contrast. Biting midges tend to be drawn to dark-colored, moving objects. This preference is thought to be because large, dark targets mimic the appearance of their preferred natural hosts, such as livestock and deer, in the visual field. Choosing lighter-colored clothing can therefore help reduce visual attraction.
The role of light is complex and depends on the midge species; while non-biting midges are strongly attracted to high-intensity white lights, biting midges show a more varied response. For biting species, light intensity signals feeding time, with low-light conditions being preferred. In terms of personal care products, some scented items like perfumes or certain lotions can contain floral or chemical components that may mimic natural attractants, although the CO2 and body odor profile are far more significant.
While some people claim to be more susceptible to bites, this variation is primarily due to differences in individual body odor, temperature, and the amount of CO2 exhaled, rather than diet or specific foods. The combination of chemical signals emitted from the skin and breath is highly individualized.