The Biology of the Mosquito: CO2 and Infrared Sensing

To a human, a Mosquito is a summertime nuisance. But to the mosquito (specifically the female, as only females drink blood), you are a massive, glowing island of resources in a dark world.

Mosquitoes do not find their prey by "Sight" in the way we understand it. They utilize a three-stage, long-range Multi-Modal Sensory System that combines chemical, thermal, and visual data to track you down with terrifying efficiency.

Stage 1: The Long-Range Chemical Sniffer (CO2)

The hunt begins at a distance of up to 100 feet (30 meters). Every time you exhale, you release a plume of Carbon Dioxide (CO2).

The Sensors: The mosquito has specialized receptors on its "Maxillary Palps" (small sensory organs near its mouth) called cpA neurons.
The Sensitivity: These neurons are exquisitely sensitive to changes in CO2 concentration. To a mosquito, your breath is a dense, invisible river of data stretching through the air.
The Trigger: The moment the mosquito hits this CO2 plume, its brain flips a behavioral switch. It stops wandering and begins to fly "Up-concentration" toward the source of the gas.

Stage 2: The Mid-Range Scent Filter

Once the mosquito gets within 20 to 30 feet, CO2 becomes too messy to follow (as it mixes with the air). The mosquito switches to its second sensor: Skin Odors.

The Cocktail: Humans secrete over 300 different chemicals from their skin. Mosquitoes are particularly attracted to Lactic Acid, Ammonia, and Carboxylic Acids produced by the bacteria living in your sweat.
The Preference: This is the biological basis for why some people get bitten more than others. People with specific skin microbiomes that produce more of these "Delicious" acids are essentially glowing brighter on the mosquito's chemical map.

Stage 3: The Short-Range Thermal Image (Infrared)

When the mosquito is within 3 feet (1 meter), it ignores the chemicals and switches to its most advanced sensor: Infrared Thermal Imaging.

The TRPA1 Channel: Just like the Pit Viper (which we discussed), the mosquito has repurposed a pain receptor (TRPA1) into a hyper-sensitive heat sensor.
The Heat Map: Even in pitch darkness, the mosquito can "See" the heat radiating from your body.
The Landing Zone: It uses this thermal map to find the perfect spot to land—specifically looking for the areas where blood vessels are closest to the skin (like your ankles or wrists), which glow "Hotter" than the surrounding tissue.

The Visual Lock: High-Contrast Motion

While following the heat, the mosquito also uses its primitive eyes.

The Attraction: Mosquitoes are highly attracted to Dark, High-Contrast Colors (like black, navy blue, and red).
The Logic: In the mosquito's visual world, a dark shape against a light background usually means a solid, warm-blooded animal. If you wear a black shirt on a summer evening, you are making yourself the highest-contrast target on the field.

Why don't you feel the bite?

To ensure it gets a full meal, the mosquito must overcome your pain and clotting systems.

The Anesthetic: The mosquito's saliva contains a mild anesthetic that numbs the area instantly.
The Anticoagulant: It also injects a protein that prevents your blood from clotting (similar to the Vampire Bat).
The Itch: The "Bump" you get afterward is not caused by the mosquito; it is your own immune system's Allergic Reaction to the foreign proteins in the mosquito's saliva.

Conclusion

The Mosquito is a high-tech tracking system in a 2-milligram package. By combining a long-range CO2 sniffer, a mid-range chemical filter, and a short-range thermal camera, it has occupied a predatory niche that is nearly impossible to escape. It reminds us that our bodies are constantly broadcasting a multifaceted signal of our existence into the environment, whether we want to or not.

Scientific References:

Luo, Y., et al. (2015). "A carbon dioxide sensor required for track-tracing in mosquitoes." Nature.
McMeniman, C. J., et al. (2014). "Multimodal integration of carbon dioxide and other sensory cues drives mosquito host seeking." Cell.
Guerenstein, P. G., & Hildebrand, J. G. (2008). "Roles and mechanisms of insect chemosensation in host seeking at plants and animals." Annual Review of Entomology. (Context on the skin odor detection).