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How big is a Dust Mite?

300 micrometers!

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Dust Mite

A house dust mite is a tiny eight-legged animal that lives in the dust of people's homes. An adult is about 0.3 millimeters long, and adults range from about 0.2 to 0.4 millimeters, barely big enough to see with the naked eye. Mites and ticks are arachnids, the eight-legged group of animals that also includes spiders.

Size

The two species most common in homes in temperate parts of the United States are the American house dust mite, Dermatophagoides farinae, and the European house dust mite, Dermatophagoides pteronyssinus. A 2013 guide for allergy doctors describes adults as oval, with creamy to see-through white bodies that measure 0.2–0.4 millimeters.

A University of Florida guide gives a larger figure: about 0.42 millimeters long for both females and males. Females are wider, about 0.32 millimeters across the body, while males are about 0.25 millimeters. The size shown here, 0.3 millimeters, is in the middle of the range from the first guide.

Size comparisons

  • A dust mite is about three times as long as a human hair is wide.
  • About three dust mites end to end would span 1 millimeter, the smallest mark on a metric ruler.
  • A dust mite is about one and a half times as long as a paramecium of a large species, which is about 0.2 millimeters long.
  • A mite's droppings are 20–40 micrometers across, so a mite is about 8–15 times as long as one of them. A micrometer is a thousandth of a millimeter.
  • If a dust mite were as long as a person 1.7 meters (5 feet 7 inches) is tall, its droppings would be 11–23 centimeters (4–9 inches) across. The largest would be about the size of a basketball.

How dust mites live

Dust mites feed on flakes of shed human and pet skin, and on the fungi, yeasts and bacteria that grow on them. They have no eyes but avoid light, so they live deep inside pillows, mattresses and carpets. A single gram of house dust can hold thousands of mites.

A mite's body is about 75 percent water by weight, and mites do not drink. Instead, they absorb water vapor from the air, which works only when the relative humidity is at least about 65 percent. Relative humidity compares the water vapor in the air with the most the air could hold. Mites do best at 75–80 percent humidity and 25–30 degrees Celsius (77–86 degrees Fahrenheit).

A mite hatches from its egg as a six-legged larva, then passes through two eight-legged stages before becoming an adult. Adults live about 4–6 weeks. A female lays one or two eggs a day, 50–80 in her lifetime.

Dust mites and allergies

Allergy specialists have recognized dust mites as the major source of allergens in house dust since 1967. An allergen is a substance that causes an allergic reaction. Most mite allergens are in the droppings, which carry digestive enzymes from the mite's gut. Each mite produces about 20 droppings a day.

When someone makes a bed or walks on a carpet, droppings rise into the air and can be breathed in before they settle again 20–30 minutes later. They can trigger asthma, a runny or blocked nose, and an itchy skin rash called atopic dermatitis. Allergy doctors advise keeping the relative humidity at home at 35–50 percent to slow the growth of mite populations.

Sources

Scale of the Universe > Dust Mite
Paramecium
Paramecia vary quite a lot in size, between 50 and 330 micrometers. These little guys are protists and like to swim in water. They can move two millimeters per second!
Ovum (Human Egg)
An ovum is the largest cell in the human body. Animals that develop within eggs within their mother are ovoviviparous, which humans are not. Ovoviviparous is the only English word starting with "vowel-v-vowel-v-vowel-v-vowel".
Thickness of Paper
Paper is very thin. It's so thin it can give you a paper cut. You can do a lot of things with paper, including writing on it, drawing on it, and even folding it into shapes like squares and triangles and dodecahedrons and others.
Amoeba
Amoebae are unicellular, which means there is only one cell. Some amoebae can grow to an incredible 700 micrometers, which is almost an entire millimeter.
Grain of Sand
Of course, not all grains of sand are the same size. They vary a lot. Arenophiles are people who collect sand samples. Also, did you know that Papakolea Beach has green sand? This is because of crystals in the sand. Whatever.
Grain of Salt
Salt is a compound made of a reactive metal and a toxic gas. Everyone knows that. Also, do not eat too much salt, or else you could die. Eating one thousandth of your body weight all at once will usually do the trick.

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