Mosquito Simulator

A female mosquito hunts a sleeper through a chain of checks. Watch which signal (her “KPIs”) makes her abandon a spot. Not a game: there is nothing to win or collect.

Auto: she decides by herself. Drag to orbit, scroll to zoom.

Keys

WASDfly, relative to the camera Space Shiftup / down Lland (within ~15 cm of skin) Phold to probe Escback to Auto
Drag to orbit the camera: the keys follow where it looks. Any move key takes her off the skin.

Scenario: your night ▾

23:00

Person ▾

Room ▾

Display ▾

Her ▾

Her checklist (gates) ▾

Humidity (info, not a gate)0 %
Humid air close to skin is a weak extra close-range cue. It is shown for the mosquito you follow, but she does not pass or fail on it in this model.
Bar = live value, white tick = her threshold. Green passes, red fails; the outlined gate is the one she is checking now. Approximate values.

Sleeper ▾

StateAsleep
Arousal0 %

Event log ▾

Mosquito drawn ×10, not to scale
her ×10, not to scale
Full. Resting for ~2 days.
Waiting for the lights to go out…

What she checks, what she does, and why it itches

The simulator above is a model. This part explains the biology behind it. All numbers are approximate, and some of the science is still unsettled. Where it is, the text says so.

1. How she finds you

Only the female bites, and she works through a chain of checks. Each check is one of the bars in the simulator’s “Her checklist” panel. When one fails, she drops back a step or gives up on that spot.

  1. Wake up. A whiff of CO₂ above the room’s background (about 400 ppm) switches her into hunting mode. In this model a rise of roughly 10 ppm or more is enough (real thresholds vary by species), and the pulses of breath work better than a steady level.
  2. Follow the plume. While she keeps hitting pockets of breath she flies upwind. If she loses it she zig-zags across the air flow to find it again, and if that takes too long she gives up and rests.
  3. Look. Once CO₂ has switched her on, dark shapes against a lighter background become interesting. Without CO₂ she ignores them.
  4. Smell the skin. Close in, skin odours take over: lactic acid, other carboxylic acids and ammonia. Repellent in the air spoils the blend, so she veers off and tries another body part.
  5. Feel warmth and moisture. Within about a metre, warm, damp skin guides the last part of the approach. Cool or covered areas are not worth landing on.
  6. Land and taste. She tastes with her feet. Repellent on the skin, thick hair or fabric thicker than her roughly 2 mm mouthparts sends her back into the air.
  7. Stay safe. Movement, breath gusts on the face and twitches make her flee. She also remembers the spot as risky for a while.
  8. Probe. She has to find a blood vessel. If she can’t, she pulls back and tries again, and after several failed tries she moves to a new spot.
  9. Drink. If she is interrupted she leaves with a partial meal and comes back later. If she gets a full meal she flies off to rest and digest for a couple of days.

2. Female vs male

The simulator has no male mosquito to play, because males never bite. They are built for a different job.

Female
Male
Both models slowly rotating, at the same scale. Look at the mouthparts and the antennae.
FemaleMale
MouthpartsPiercing: a bundle of six thin stylets inside a sheathCan’t pierce skin; the cutting parts are reduced. Long, hairy palps beside it
AntennaeSparsely haired, packed with smell and heat sensorsFeathery and bushy: they work as ears that pick up a female’s wing tone
DietNectar and plant sugar for energy, plus blood for the protein to make eggsNectar and plant sugar only
Wingbeat pitchAbout 400–600 Hz: the whine you hear at nightHigher pitched
LifespanSeveral weeks, with several egg cycles (blood meal, rest, lay eggs, hunt again)About a week
Built forFinding a host, drinking blood, making eggsFinding a female and mating

3. During a bite

What looks like a single needle is a tool kit. The visible “proboscis” is mostly the labium, a soft sheath. It does not go into the skin. It folds back like a bent knee while the six stylets inside it slide in.

1 2 3 4 5 6 7 8
  1. Labium, the sheath. It stays outside and bows back as the stylets go in.
  2. The stylet bundle: six stylets working together.
  3. Saliva pumped in while she probes.
  4. A capillary, the target.
  5. Epidermis, the outer skin.
  6. Dermis, where the small blood vessels and the immune cells are.
  7. Earlier probe tracks. She pulled back and tried another direction.
  8. Cross-section of the bundle: 2 maxillae with saw-tooth tips that cut in and anchor, 2 mandibles, the labrum, a gutter that forms the food canal (blood goes up), and the hypopharynx, a separate saliva channel (saliva goes down).
Schematic, not to scale. Her head is shown hugely magnified.
  • Saliva first. Her saliva contains anticoagulants so the blood doesn’t clot, vasodilators that widen the vessels, and factors that stop platelets from sticking. It also contains foreign proteins, and those are what your immune system reacts to afterwards.
  • Searching for blood. The tip of the bundle bends and probes through the dermis. She can pull back and re-probe in a new direction several times. She drinks either straight from a capillary or from a small pool of blood leaking around the tip.
  • Tasting blood. Sensors at the tip recognise blood by chemical cues such as ATP and salts. That is how she knows she has hit the right fluid and not just tissue.
  • The meal. She can take up about two to three times her own body weight in blood, in a minute or two.
  • Knowing when to stop. Stretch receptors in her abdomen signal “full”. A full female flies off heavily and rests for a couple of days while the eggs develop.

In some parts of the world this same saliva route is how mosquitoes pass on diseases such as malaria and dengue.

4. Afterwards: why it itches and swells

The bump is your immune system reacting to her saliva proteins, not damage from the stylets. It usually comes in two waves.

  • Immediate (minutes). If you have antibodies (IgE) against her saliva, they sit on mast cells in the skin. The mast cells release histamine, which causes a pale, raised wheal with a red flare and itching. It peaks within about 20 minutes and fades within hours.
  • Delayed (a day or two). Immune cells, mainly driven by T cells, gather at the bite. This gives a firmer, red, itchy bump that builds over the next day, peaks around 24–48 hours and can last several days.
  • Why a break can matter (hedged). People bitten often by the same kind of mosquito can slowly become less reactive. After a long break, some of that tolerance may fade, so the first bites of a season can react more strongly. This pattern is described in the medical literature, but it varies a lot between people, and nobody can say that exactly two months is enough to change anything.
Immediate whealDelayed reactionItchUntouched bite
Close-up, about 3 cm across
Illustrative, not measured. These curves have a textbook shape chosen to show the idea. They are not data from patients, and real reactions vary a lot from person to person.

The “16 h” marker is where your own bites were when you noticed them itchy and swollen. That is on the rising slope of the delayed reaction, so they may get a little worse before they get better.

5. Do’s and don’ts

Do

  • Cool it. Use a cold pack or a cold wet cloth (wrapped, not ice directly on skin) for about 10 minutes. It calms the itch and the swelling.
  • Hydrocortisone 1% cream from the pharmacy, a thin layer once or twice a day for a few days. It damps the delayed swelling. Follow the packet.
  • An oral antihistamine such as cetirizine or loratadine if you react strongly or have many bites. It works best taken early.
  • A pharmacy anti-itch gel or lotion for short-term relief.

Don’t

  • Don’t scratch. Scratching releases more histamine, makes the bump bigger and itchier, and can break the skin and let bacteria in. Keep nails short, or cover the bite at night.
  • Don’t rely on heat pens. The evidence for them is weak, and they can burn if used carelessly.
  • Skip home remedies such as toothpaste. They don’t really work and can irritate the skin.
See a doctor if the redness is spreading, you get a fever, there is pus, or the swelling is still growing after 2–3 days. Get urgent help for trouble breathing or swelling of the face or throat.

This page is not medical advice.

6. Why me?

Some people really are bitten more than others, and in tests they tend to stay that way. Here are the factors, roughly ordered by how strong the evidence is. The buttons load a version of the person into the simulator and restart the night.

  1. Strong Skin chemistry and skin bacteria. The best evidence for “mosquito magnets”. In a multi-year study (De Obaldia et al. 2022, Cell), the most attractive people had much higher levels of carboxylic acids on their skin, and stayed attractive over years. Skin bacteria turn sweat into many of these odours.
  2. Strong CO₂ output and body size. CO₂ is how she finds anyone from a distance. Bigger bodies, and a higher metabolism (after exercise, in pregnancy), put out more of it, so they are found sooner. It gets you noticed, but your skin decides a lot of what happens up close.
  3. Good Heat and sweat. Warm skin, moisture and lactic acid after exercise all help her in the last metre.
  4. Moderate Pregnancy. In a field study, pregnant women attracted about twice as many malaria mosquitoes, probably because they breathe out more CO₂ and are slightly warmer.
  5. Moderate Genetics. Twin studies suggest that how attractive you are is partly inherited, probably through your body odour.
  6. Limited Beer. A couple of small studies found people more attractive after drinking beer. The reason is unclear. (The “after a run” button above includes a beer.)
  7. Weak Blood type. The claim that type O is a favourite rests mostly on one small study (Shirai et al. 2004, with Aedes albopictus), which found more landings on type O. Other work is mixed. She has no known way to read your blood type through the skin. One idea is that some people (“secretors”) put blood-group substances onto their skin, which could change how they smell. In the simulator it is off by default.

So, blood type or CO₂? CO₂ gets you found. Skin chemistry is the best-supported reason one person gets bitten more than the person next to them. Blood type is the weakest explanation of the lot.

Your night, explained

The face. Your breath is the CO₂ source, so she kept coming to your nose. Up close, though, every exhale is a gust in her face, and small twitches and half-waking made the spot fail her safety check. Lots of approaches, no bite.

The arms. Arms lying still outside the blanket are warm, bare, smell of skin and don’t breathe at her. They pass every check, so that is where she bit.

The second bite, hours later. There are two plausible stories, and the simulator can show both. In the first, one interrupted mosquito was disturbed mid-meal by a twitch or by you turning over. She left with a partial meal, rested, and came back hours later for the other arm, steering clear of the one where she had been disturbed. In the second, there were two mosquitoes. The cream had nothing to do with it: hydrocortisone is not a repellent.

Itchy at 16 h. That is the delayed reaction building. After two months without bites, it may also be a bit stronger than usual (see section 4).

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