Mosquitoes use their sophisticated sense of smell to locate hosts, a vital ability for their survival. Female mosquitoes need a blood meal to produce eggs, actively seeking out sources by detecting chemical signals from living organisms. Understanding how they perceive these scents explains their remarkable ability to find us.
Human Scent Signatures
Female mosquitoes are drawn to humans by a distinct blend of chemical compounds that form our unique scent profile. One primary long-range attractant is carbon dioxide (CO2), which humans exhale. Mosquitoes detect CO2 plumes from significant distances, sometimes over 100 feet away, using it as an initial signal that a potential host is nearby and activating their search behaviors.
As mosquitoes get closer, they detect specific chemicals on human skin and in sweat. Lactic acid, a byproduct of human activity in sweat, is a strong attractant, especially when combined with carbon dioxide. Another group of attractants includes carboxylic acids, produced on the skin by bacteria. These fatty acids contribute to individual body odor and are appealing to mosquitoes.
Ammonia, a metabolic byproduct in sweat, further contributes to human attractiveness. While ammonia alone may not be highly attractive, it can act synergistically with lactic acid to enhance its appeal to certain mosquito species. Beyond these specific compounds, human skin releases many volatile organic compounds (VOCs), creating a complex chemical cocktail. This intricate blend, influenced by factors like diet, genetics, and the skin’s microbiome, forms an individual’s unique scent signature.
Individual differences in this scent profile explain why some people are more attractive to mosquitoes than others. For example, individuals who produce higher levels of certain carboxylic acids tend to be more appealing. Factors such as a higher metabolic rate, increased body temperature, or pregnancy can also lead to greater CO2 exhalation and increased sweat production, making individuals more detectable. The composition and diversity of bacteria living on human skin also play a role, as these microorganisms metabolize sweat components into attractive odorants.
Beyond Human Odors
Mosquitoes are not solely attracted to humans; their diets and life cycles also draw them to other biological scents. Both male and female mosquitoes rely on plant-derived scents, particularly from flowers, for their primary energy source: nectar. Nectar provides essential sugars for survival; males feed exclusively on it, while females consume it for most of their lives outside of blood-feeding periods. Mosquitoes are attracted to specific floral odors, which guide them to nectar sources.
Mosquitoes also feed on various animals, and general animal odors can serve as attractants. Different mosquito species exhibit preferences for different host animals, including amphibians, reptiles, birds, and various mammals. Some species may initially feed on birds but shift to mammals, including humans, as their populations grow. The chemical compound nonanal, found in exhaled breath, has been identified as a key attractant for certain mosquito species that feed on both birds and humans.
While not scents, humidity and heat are important environmental cues that mosquitoes use in conjunction with odor to locate a host. Mosquitoes thrive in warm, humid conditions, which can enhance their sensory abilities. They can detect the moisture and heat emanating from a body, especially at closer ranges. These physical cues integrate with chemical signals to help mosquitoes pinpoint a landing site.
How Mosquitoes “Smell”
Mosquitoes possess specialized biological structures to detect the array of attractive smells in their environment. Their primary olfactory organs are the antennae, which are covered with hair-like structures called sensilla. These sensilla house olfactory receptor neurons (ORNs), which are specialized nerve cells designed to detect specific chemical compounds. Mosquitoes also have olfactory receptors on their maxillary palps and proboscis, further expanding their sensory capabilities.
When odor molecules enter the sensilla, they bind to specific olfactory receptors located on the ORNs. This binding process triggers electrical signals in the neurons. These signals are then transmitted to the mosquito’s brain, where olfactory information is processed. The brain interprets these signals, allowing the mosquito to identify the source and concentration of the smell.
Mosquitoes integrate multiple sensory cues to accurately locate a host. For instance, the detection of carbon dioxide can “prime” the mosquito’s visual system, causing it to scan for shapes associated with potential hosts. The brain combines information from chemical odors, heat, moisture, and visual cues to create a complete “host signature.” This multimodal integration enables mosquitoes to efficiently track and home in on their targets, even in complex environments.