We generally use the term biodiversity to refer to the wealth of organisms that inhabit wild ecosystems, such as forests or reefs. However, human constructions are also ecosystems, artificial and man-made, but ecosystems just the same, which can also be inhabited by some animals.

Shelter, temperature, food and humidity
Species that appear in cities taking advantage of the conditions created by man are called synanthropic, and those that end up living in cities are called urban or synurban species. The favorable indoor conditions for certain animals have to do with three parameters: shelter, temperature and food.

Beyond our pets, there are few animals that we see easily and many that actually live inside our homes. In other words, this means that there is not much interaction between them and humans: most of them take advantage of the conditions we provide them without us noticing. In many cases, our homes are a last refuge for them because they would not be able to survive outside.

There is a fourth parameter that usually explains the presence of some groups only in certain areas of the house: humidity. We will find animals in damp bathrooms due to the use of bathtubs or showers that will not be in other parts of the house.

The skewed distribution of animals in the different premises depends on the presence or absence of food, which is important to explain situations we call "pests" and to recognize their identity down to the species level.

Many of these animals are tiny, so we do not realize that they live next to us. They are the protagonists of this article.

Dust mites
They are like small spiders that we can find taking advantage of the organic subject that we leave in the corners, also in our beds; it is the reason for the presence of "dust mites", which are only annoying for people allergic to their hairs.

Spiders
Present in corners (especially high up), they can serve as natural traps for other animals more annoying than themselves, such as mosquitoes. They are one of the most important groups in homes and, together with ants, beetles and flies, account for 73% of the "encounters" in a typical home.

Mealybugs
They are crustaceans and breathe through gills. That is why they are only present in very humid places, as they need to obtain oxygen from humid air.

Springtails
They are little known and yet they are abundant in the soil and in the soil of our pots, as they are closely related to the fungi that grow in any place with permanently high humidity.

Silverfish
Related to springtails, silverfish feed on the organic subject that remains in the corners, especially in bathrooms where there is the humidity they need to develop their life cycle.

Insects
There are different groups of insects that we can find in houses for different reasons. Crickets come in from gardens looking for shelter.

The elusive cockroaches are among the few groups that are dangerous because of their ability to bring pathogens to us by moving between food products and sewage systems full of undesirable microorganisms.

Termites - nowconsidered social cockroaches -can be a serious problem at Structures wood.

Mealybugs and aphids are hemiptera that can feed on our indoor plants, often tropical plants inside houses located in places that are not tropical.

Bed bugs feed on blood, so they can transmit serious diseases. And we can also find "vegetarian" bedbugs that are only in homes in winter, fleeing from the cold temperatures outside.

Lice also feed on blood by gnawing on the scalp, especially of children.

Psocoptera, or book lice, are related to fungi that may be growing in damp libraries.

There are moths that feed on wool, and therefore spoil our clothes, and there are also others capable of feeding on nuts or floury products (there are never "moths" in wood).

There are larvae of small flies feeding in the substrate of our pots, and others are present in the fruit when overripe, such as the Mediterranean fruit fly or the vinegar fly.

The cosmopolitan house fly is a frequent visitor to the outdoors seeking pleasant temperatures and shelter.

Ants wander through houses in search of food in the pantries, but always make their nest outside.

Finally, beetles include species that can be on our food, and also on building materials, as in the case of woodworm.

Biodiversity and humans
Even extreme cleanliness does not completely prevent the presence of these inhabitants, but that's okay: in most cases they do not pose any danger and eliminating them with toxic chemicals is not advisable.

There are species, which we can consider cosmopolitan, that can live in homes in different parts of the world, but others prefer a certain subject climate. The arrival of some species to other countries has accelerated in recent years due to the greater mobility of people, both in issue and in the frequency of travel. Some may become invasive species , as is the case of the termite Cryptotermes brevis, originally from South America.

The presence of a wide variety of living things, even in the urban environment, is good news. And the presence of animals in our homes is a good reminder of where we come from: nature.

............................................

Enrique Baquero researcher of Biodiversity and Environment Institute (BIOMA) and professor of the School of Sciences, University of Navarra 29.07.2024