How Do Mosquitoes Find Hosts by Carbon Dioxide?

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Mosquitoes find animals to bite by combining several cues, and carbon dioxide is one of the most important of them. The short answer to how do mosquitoes locate hosts by carbon dioxide is that carbon dioxide works as a long-range signal, telling the insect that a warm-blooded animal may be nearby. Once a mosquito is close, other cues such as body odor, heat and moisture take over. This article explains that sequence using two research papers: an experimental study of Aedes aegypti mosquitoes and a review of host-finding behavior across mosquito species.

Quick answer

• Carbon dioxide is a long-range cue. It “activates and induces upwind flight” according to one review.
• Carbon dioxide alone does not identify a suitable host, so mosquitoes combine it with other cues.
• Close to a host, heat, moisture and skin odour cues guide the final approach and the choice of landing and biting site.
• Experiments show that carbon dioxide and human odor interact, so the signals work together rather than one at a time.

Why carbon dioxide is a key cue

Carbon dioxide has been studied heavily as a mosquito signal. One review states that “carbon dioxide is the best-known mosquito kairomone and its role in mosquito host location has been intensively studied.” The review describes carbon dioxide as “a general cue indicative of the presence of a vertebrate host.”

The same review also gives a sense of range. It states that “host recognition through changes in CO 2 levels usually occurs over distances of approximately 10 m when the ambient CO 2 level changes by the addition of a breath plume containing ~ 4% CO 2.” That range is why the review treats carbon dioxide as a long-range cue.

The review also reports that mosquitoes can detect small changes. It says that “mosquitoes have been shown to respond to very small changes in atmospheric CO 2 concentrations.” A cue that can be sensed at low levels gives the insect an early signal to move toward the source.

From a faint signal to upwind flight

A carbon dioxide signal does not tell the mosquito where the host is. It tells the insect that something useful may be nearby, and the next step is movement. The review describes the first stage as “long distance chemical stimulants (such as CO 2 , that activates and induces upwind flight).” That phrase describes the basic plan: detect the plume, then fly into the wind toward its source.

This is a stage of host-seeking rather than the whole process. The review lists several behavioural cues used during host-seeking, including “visual cues, long distance chemical stimulants (such as CO 2 , that activates and induces upwind flight), heat and moisture cues that play an important role in behavioural responses in close vicinity of the host, and skin odour cues that influence landing and biting site selection.” Each cue is tied to a different range or decision, which is how the signals divide the work.

Why carbon dioxide is not enough on its own

The review explains why mosquitoes do not rely on carbon dioxide alone. It states that “carbon dioxide is a general cue indicative of the presence of a vertebrate host but mosquitoes do not only rely on CO 2 because it does not convey information on the potential suitability of the host.” A plume tells the insect that a vertebrate may be there, but not whether that animal is a good source of blood for that mosquito.

The experimental paper points to the same combination. It describes female mosquitoes as integrating “an array of sensory information to find their human hosts including carbon dioxide (CO 2 ), body odor, heat, moisture, and visual cues.” The paper’s main point about carbon dioxide is that it sensitizes the insect to other signals. It states that “the genetic interactions of Ir8a and orco as well as Ir8a and Gr3 suggest a crucial role for CO 2 to sensitize mosquitoes to human odor and highlights the importance of human acidic volatile detection during mosquito host-seeking.”

The same paper gives a behavioural result that shows the interaction. It reports that “in the absence of CO 2, orco mutants lose strong attraction to human odor.” In other words, the human-odor response depends on the carbon dioxide context in these experiments. The paper’s wording is about mutant lines of Aedes aegypti, so the result describes that species under those test conditions.

What happens close to the host

When a mosquito is near a host, the cues change. The review places “heat and moisture cues” in “close vicinity of the host.” It also places “skin odour cues” with the decision about where to land and bite, since they “influence landing and biting site selection.” The early signal starts the flight, and the closer cues steer the final steps.

The experimental paper also describes an earlier finding that narrowed the question. It states that “previously, the functional ablation of a family of Aedes aegypti olfactory receptors, the Odorant Receptors (ORs), was not sufficient to reduce host-seeking in the presence of carbon dioxide (CO 2).”

How we chose

The two sources were chosen because each is a research paper on mosquito host-finding and each was opened directly from its PubMed Central page. One is an experimental study of Aedes aegypti behaviour and receptors. The other is a review of semiochemicals and host selection across mosquito species. Both pages returned HTTP 200 on a direct request without redirects, and each quote was copied from the fetched text. No retail pages or product listings were used.

What we could not verify

The experimental paper is about one species, Aedes aegypti, and the review covers several species. The article describes each claim as the source reports it.

What the sources do not say

The fetched sources do not give a single distance for every mosquito species or every weather condition. The review’s range figure comes from a specific breath-plume example. The sources also do not describe how wind direction changes the plume shape in a yard, so those details are not included here.

Frequently asked questions

Do mosquitoes find people only by carbon dioxide?

No. The review states that “mosquitoes do not only rely on CO 2 because it does not convey information on the potential suitability of the host.” Other cues such as body odor and heat are used as well.

How far away can a mosquito detect a breath plume?

The review says host recognition “usually occurs over distances of approximately 10 m” when a breath plume changes the ambient carbon dioxide level. This is a typical figure from the source, not a fixed limit.

Does carbon dioxide make a mosquito fly toward a host?

The review describes carbon dioxide as a long-range stimulant that “activates and induces upwind flight.” It is the first step in that movement.

Which cues guide a mosquito once it is close to a host?

The review places “heat and moisture cues” in “close vicinity of the host,” and “skin odour cues” with landing and biting site selection.

Do mosquitoes respond to small changes in carbon dioxide?

The review states that “mosquitoes have been shown to respond to very small changes in atmospheric CO 2 concentrations.” The source does not give one threshold value in the fetched text.

For related reading on insects in the garden, see how to attract native bees and how to attract hummingbirds to your yard.

Sources

• Aedes aegypti mosquitoes detect acidic volatiles found in human odor using the IR8a pathway. PubMed Central, https://pmc.ncbi.nlm.nih.gov/articles/PMC6482070/ (opened 2026-10-28).
• Controlling mosquitoes with semiochemicals: a review. PubMed Central, https://pmc.ncbi.nlm.nih.gov/articles/PMC7027039/ (opened 2026-10-28).