Mosquitoes are a common nuisance, and their bites can lead to discomfort and, in some cases, transmit diseases. While many factors contribute to their ability to find a host, scent plays a primary role in attracting these insects. Understanding the science behind what draws mosquitoes to humans reveals a complex interplay of chemical cues that guide their relentless pursuit.
Key Odor Attractants
Mosquitoes are primarily drawn to specific chemical compounds emitted by humans and other animals. Lactic acid, a substance found in human sweat, is a significant attractant for various mosquito species, including those that transmit diseases like malaria and dengue fever. Ammonia, released through the skin, especially with increased sweat production, also functions as an attractant. While ammonia alone may not be effective, it becomes attractive when combined with lactic acid.
Fatty acids emanating from the skin also create a strong allure for mosquitoes. These carboxylic acids are produced when the beneficial microorganisms living on human skin break down sebum, a waxy coating. This process generates odors similar to cheese or smelly feet, which are highly attractive to mosquitoes. Additionally, compounds like octenol, acetone, sulcatone, uric acid, and nonanal, present in human breath and skin, contribute to the overall attractive scent profile.
How Mosquitoes Detect Scents
Mosquitoes possess specialized sensory organs that enable them to detect these chemical cues with remarkable precision. Their main olfactory organs are the antennae, which are densely populated with olfactory receptor neurons. These neurons express odor-gated sensory receptors that bind to specific odor molecules. When these receptors bind to chemical ligands, they transmit signals to the mosquito’s brain, allowing the insect to process and interpret the scent information.
The maxillary palps, located between the antennae, also play a role in scent detection, particularly for carbon dioxide. Three main classes of odor-gated receptors have been identified in mosquitoes: odorant receptors (ORs), olfactory gustatory receptors (GRs), and ionotropic receptors (IRs). ORs respond to a variety of human skin emanations, while olfactory GRs detect carbon dioxide. Mosquito IRs are responsive to acids and amines, suggesting their involvement in human host preferences. This intricate sensory system allows mosquitoes to effectively locate potential blood meal sources.
Beyond Odor: Other Attracting Factors
While scent is a primary attractant, mosquitoes employ a combination of cues to pinpoint their hosts. Carbon dioxide (CO2), exhaled with every breath, acts as a significant long-range signal.
Mosquitoes can detect CO2 from considerable distances, up to 50 to 100 feet away. This CO2 plume often serves as the initial cue, drawing mosquitoes towards a potential host. As mosquitoes get closer, they begin to sense body heat.
Human skin emits infrared radiation, which mosquitoes can detect, especially when the environmental temperature is lower than skin temperature. This thermal detection helps them hone in on the precise landing spot. Visual cues also play a role, particularly at closer ranges. Mosquitoes are attracted to movement and dark-colored clothing, such as red, orange, black, and cyan, while ignoring colors like green, blue, and purple. These visual signals, combined with odor and heat, guide the mosquito to its final target.
Why Individuals Differ in Attractiveness
The common observation that some individuals are more prone to mosquito bites than others stems from a unique combination of personal factors. Variations in the composition of an individual’s skin microbiota significantly influence their body odor profile, which in turn affects mosquito attraction. The specific types and amounts of bacteria on a person’s skin can create distinct fragrances, making some individuals more appealing.
Genetic predispositions also play a role in determining attractiveness. Genetics can impact the amount of certain chemicals, such as uric acid, emitted through the skin. Metabolic rates, which affect CO2 output, also contribute to individual variability; larger individuals or those exercising tend to emit more CO2, making them more attractive. These combined factors create a unique “scent signature” for each person, explaining why mosquitoes show varying preferences among individuals.