House Dust Mite
House Dust Mites (HDM) are a major source of allergen and found in temperate and humid areas. There is widely published data that shows how House Dust Mite avoidance can reduce exposure to allergens.
House Dust Mites are arachnids not insects and related to ticks and spiders such as daddy long legs. Thirteen species of HDM have been found in dust however the two which are the most common and are the main source of the HDM allergen are Dermatophogoides farinae and Dermatophadoides pteronyssinus from the family Pyroglyphidae. The life cycle of the HDM Dermatophagoides pteronyssinus consists of 5 stages:
The adult mated female can lay 40 – 80 eggs in her lifetime, when the egg hatches a six legged larva emerges. There are two nymphal stages which feed and moult before an eight legged adult is developed. The adult HDM has a mouth-like appendage and no eyes or antennae. The duration of the cycle is usually one month and dependent on the climate, ideally 25°C and 75% RH. An adult HDM can live for one to three months under favourable conditions.
Their translucent body is 300µm – 400µm in length and only visible under a microscope with the faecal pellets ranging from 20µm – 50µm, it is estimated that the HDM can produce 20 pellets per day. HDM are ~75% water by weight and therefore need to absorb water from the water vapour in the air making relative humidity a critical factor for survival.
