House dust mites are small arthropods that belong to the subclass Acari (also known as Acarina) and the class Arachnida. They are very common in households – hence the name – and they are supposed to have lived on Earth for over 23 million years. The two most common species of house dust mites are the North American house dust mite (Dermatophagoides fariane) and the European house dust mite (Dermatophagoides pteronyssinus).
Description and distribution
They can be described as microscopic spiders, as they have oval-shaped, semi-transparent bodies, of a translucent creamy white colour, with very fine stripes. They are wingless and have hair on their body and their legs. Typically, adults measure around 0.4 millimetres in length and 0.2 – 0.3. millimetres in width, while youngsters are even smaller.
Due to their size, they are very difficult to spot with the naked eye; in fact, in order to be correctly identified, a magnification of the image of at least 10 times is necessary. Therefore, if you can see a mite without a magnifying glass, they are probably a completely different species, and not a house dust mite.
As previously mentioned, house dust mites are a cosmopolitan species in human households, living in colonies and thriving in the humid environments provided by rooms such as bedrooms and kitchens. More specifically, they survive well in bedding (pillows, duvets, sheets, blankets, etc.) mattresses, upholstery, soft toys, curtains, carpets (especially long-fibered ones), and furniture; they attach themselves to the fibres and live comfortably, to the point where a single gram of dust can contain anywhere between 100 – 500 dust mites.
Despite warmth and humidity being preferred, the existence of house dust mites is not limited to wet climates; a temperature of 18 – 26°C and a humidity level that is higher than 50% generally constitute a perfect environment, but they can be found even in dry climates and at high altitudes, surviving and reproducing relatively easily in carpets and beddings (especially pillows), seeing as these are the objects that most often come in contact with and retain human moisture.
Breeding and dietary information
A house dust mite’s life consists of five main stages: egg, larvae, protonymph, tritonymph, and adult. The transition between stages happens through moulting; in appropriate environments, the entire development, from egg to adult, can happen within a month. Male house dust mites live around 10 – 19 days, while female house dust mites live longer, up to 70 days, laying between 60 – 100 eggs in the last 5 weeks of life.
House dust mites feed on different types of organic detritus, including (but not limited to) molds, fungi, bacteria, dead mites, pollen, and even dead skin cells, the latter of which can be considered their favourite food. A human being sheds approximately 0.3 – 0.4 kg of skin cells per year, which is more than enough to feed a million house dust mites. Like many decomposer animals, they select food that has already been partially broken down by fungi (usually molds). Their digestion is also incomplete; mites’ intestines lack the ability to absorb all available nutrients, so some substances are consumed more than once, with the help of powerful enzymes that are placed in droppings and that act to break down the leftovers and turn them into more nourishment.
House dust mites as pests
House dust mites are a common problem in households because the usual cleaning methods (such as hoovering, wiping dust, etc.) and products are not effective in removing them; the same can be said about insecticides. Although house dust mites do need a certain degree of warmth and humidity to survive, as previously mentioned, a drop in both cannot guarantee a complete elimination; this can only prove effective if drastic and, even then, only after a period of time of couple of months has passed, seeing as they usually manage to survive by retreating towards the inside of pillows and carpets.
As opposed to other species of mites, such as scabies mites, house dust mites do not burrow under the skin, do not sting, do not bite, and are not parasitic, but that does not mean they are not pests; on the contrary, they are a common cause of asthma, chronic rhinitis, as well as allergic symptoms in general. The main reason is because the mites’ guts contain potent digestive enzymes (the most notable of which are proteases) that are eliminated through and persist in faeces, which enables them to be easily breathed in by people, causing allergic reactions. What’s more, these enzymes stay in the dry droppings until they meet a moist surface, and if the surface in question happens to be human tissue, the enzyme will attach to it and become active once again, which can create irritation and rashes. The same can be said about the mites’ exoskeletons and other secretions. All of these particles mix to create a fine dust that is aptly referred to as house dust and that is very easily stirred when performing even the most basic of actions, such as hoovering, sweeping the floor, walking across the carpet and even shifting during sleep.
To further understand the problem that such small beings can cause, specifically to highly allergic people, it is important to mention that, in a 10-week lifespan, an average house dust mite will produce approximately 2.000 faecal particles and even more partially digested, enzyme-covered dust particles, which continue to cause allergic symptoms even once the mite itself has died. Here are a couple of symptoms that exposure to house dust mites might bring:
- a tight feeling in the chest area;
- runny nose;
- itchy nose;
- itchy eyes;
- itchy skin;
- skin rashes.
Children are particularly vulnerable, not only because they spend much more time in bed, but also because they are unable to recognise the allergic symptoms, much less understand what measures need to be taken to alleviate them. In highly allergic, hypersensitive individuals, inhalation of house dust can result in acute attacks of bronchial asthma and, in the worst of situations, perhaps even death.
Furthermore, although they, themselves, do not bite, as was said, some research points towards the fact that the active digestive enzymes found in droppings can kill delicate defence cells and enter the human body, continuing their journey through the blood stream.
Avoiding exposure to dust mites is the best strategy for controlling dust mite allergy. In order to do this, you need to decrease the humidity in your house and improve ventilation, use dust-proof or allergen impermeable covers, wash beddings in hot water and reduce clutter around the house. These are just a few preventive measures that you can take against an infestation. For more details, you can check our related article about how to ‘Prevent infestation with Dust Mites’, and for details on ‘How to get rid of Dust Mites’, you can also find a list of actions you need to take inside the house, to be able to eliminate the risk of allergies and the presence of house mites. Acting quickly and thoroughly against these pests can get you rid of infestations, however, mites can easily come back. Remember to always keep a good level of sanitation and combine exclusion methods with preventive ones, as this is the only way of keeping your house secure of these critters.