Mosquitoes are host-seeking insects; only the female requires a blood meal to develop her eggs. She uses a sophisticated sensory system to locate a host, which is the foundation for effective control and targeted trapping technology. Host-finding is a sequence of sensory cues, beginning from a distance and narrowing down to the final target using chemical and thermal signals.
The Primary Attractant: Carbon Dioxide
The initial, long-range cue that alerts a female mosquito to a potential host is the plume of exhaled carbon dioxide ($\text{CO}_2$). This gas is universally emitted by all vertebrates, making it a reliable signal for a blood source, detectable from up to 100 feet away. The detection mechanism relies on a pair of sensory appendages near the mouth, called the maxillary palps. These palps are equipped with neurons sensitive to minute shifts in $\text{CO}_2$ concentration, allowing the mosquito to follow the invisible gaseous trail. As a host breathes, the $\text{CO}_2$ forms a cone-shaped plume that the mosquito follows upwind, using the increasing concentration to guide her flight path toward the source.
Close-Range Signals: Heat and Body Chemistry
Once a mosquito enters the $\text{CO}_2$ plume and is within a few feet of the host, she switches to short-range attractants. These cues include a complex cocktail of chemicals emanating from the skin, sweat, and breath. Potent chemical signals include $\text{L-lactic acid}$, Octenol (1-octen-3-ol), and acetone, all byproducts of human metabolism. $\text{L-lactic acid}$ is present in sweat, especially after physical activity, and Octenol is a volatile chemical found in both breath and sweat. The skin’s microbial community converts compounds in sweat into volatile organic compounds, such as carboxylic acids, which form an individual’s unique scent signature. Body heat and moisture serve as final-stage attractants. Thermal sensors detect the warmth of the skin, and moisture confirms the presence of a living body surface, leading to the decision to land and probe.
Translating Biology into Trapping Technology
Effective mosquito control devices translate the female mosquito’s host-seeking biology into a functional trap. Commercial traps are designed to mimic a host by generating the three primary attractants: $\text{CO}_2$, heat, and chemical odor. These traps commonly use propane gas, which is catalytically converted to produce a steady, warm stream of $\text{CO}_2$ that mimics human breath. This $\text{CO}_2$ plume draws mosquitoes from a wide area toward the trap. To complete the illusion, chemical lures, typically cartridges containing Octenol, $\text{L-lactic acid}$, or a specialized blend, simulate the close-range body odor signature. The trap also incorporates a heated surface or dark color to replicate the thermal and visual cues of a warm body. Once lured close, a powerful vacuum fan draws the insect into a collection net, container, or onto a sticky surface, removing them from the reproductive cycle.
Common Misconceptions About Mosquito Attraction
Many common household pest control devices are ineffective against mosquitoes because they fail to utilize the correct biological attractants. Standard $\text{UV}$ light bug zappers, for instance, operate on the principle that insects are drawn to ultraviolet light. While this attracts many nocturnal insects, mosquitoes are not primarily attracted to $\text{UV}$ wavelengths. Studies show that $\text{UV}$ zappers kill a large number of non-biting and beneficial insects but are poor at attracting female mosquitoes. One study found that less than 6% of insects killed by zappers were biting flies, including mosquitoes. The mosquito’s visual preference is secondary to chemical cues, but they are generally drawn to dark colors. Dark colors provide a high-contrast target against the horizon, which is why dark clothing can sometimes result in more bites.