By Ella Davies
Earth News reporter
Dust mites "swarm" around houses, migrating as a group in search of moisture, according to a new study.
The collective movement happens when mites leave a dry area in search of higher humidity - the greatest source of which in a house is its human occupants.
Mites gain nutrients from dead skin but also depend on moist air for survival.
Millions of dust mites are found in the average home and their droppings are known to trigger asthma attacks.
DUST MITE FACTS
House dust mites are acari, a subclass of arachnids and have eight legs
At less than half a millimetre in length, they are barely visible to the naked eye
The human immune system can "recognise" the mites and produce antibodies in response. This can trigger an allergic reaction
In findings published in the journal Ethology, scientists reveal the previously unknown sociable side of house dust mites (Dermatophagoides pteronyssinus).
"We expected the mites to move to areas of higher humidity, because they are dependent on air moisture to survive," said co-author Anne-Catherine Mailleux.
"However, the fact that they attract each other and prefer to move together rather than independently from one another was an important finding."
Researchers knew that house dust mites were unable to drink and depended on moisture in the air to survive.
During their study they observed that male adult mites and nymphs moved as a group from a dry area in search of higher humidity.
When offered the choice of more than one path providing access to moister air, mites were able to perceive which branch previous mites had chosen. More often than not, they then followed these other mites.
The study showed that, by tending to choose the same routes, dust mites travel collectively or "swarm".
Although usually associated with flying insects, swarming is defined as the collective movement of a large number of organisms.
This behaviour has been observed in a variety of species but was unknown in dust mites.
"So far, mites had not been considered as "social" animals, and this is the first study that shows that they tend to stick together when on the move," explained Ms Mailleux.
"This suggests that they need each other for some reason, that they are better in a group than alone."
House dust mites are barely visible to the human eye, measuring less than half a millimetre long.
Millions can be found in the average home in Europe, Asia and the US.
Due to their need for moist air, they are most often found in bedding such as pillows and duvets.
Their droppings are a known trigger for attacks amongst asthma sufferers.
In allergic individuals the human immune system can identify mite droppings as a threat and creates antibodies to fight it, causing irritation to the airways.
The behaviour of house dust mites is therefore of considerable interest to those studying allergies.
"Knowing how mites behave can be very helpful when taking measures to prevent their populations from growing," says Ms Mailleux.