With the arrival of warm weather, in spring and summer, mosquitoes and other insects arrive. Do they arrive? No, they were already among us overwintering (usually in egg form), waiting for the moment to reactivate their growth.

Mosquitoes bite us to feed our blood to their larvae. And some of them can carry organisms that can cause us diseases (viruses and protozoa) and this is what we call "vectors" of diseases. This is the case of malaria, yellow fever, Chikungunya, or Zika. Not all mosquitoes are vectors, because they have to combine the ability of the pathogen to survive inside them (each species of mosquito is capable of harboring some pathogens but not others) and actually acquire it when feeding on the blood of a sick person.

There are other, less visible insects that can also cause damage. Moth larvae can bore holes in our clothes. Weevils (the name given to any insect that can bore holes in something) bore holes in our grain. Woodworms cause our wooden belongings to gain or lose value, and termites can tear down our house without us realizing it. We even have specialists in eating the books in our libraries. Some species make life impossible for farmers, insisting on eating our crops, and others change the color of our forests by eating the leaves of trees or carrying pathogens that make them sick. Some of these species were "born" here, but usually the most harmful ones come from distant countries and, when they arrive, they do not find skill to carry out their misdeeds (this is what we call Invasive Alien Species).

According to a recent study, we are experiencing the greatest extinction of insects since the Cretaceous (145 Ma ago). And insects have been on earth for almost 500 Ma. The most important causes (accounting for 50%) are intensive agriculture, pesticides and other environmental changes. If we add urbanization, fertilizers and deforestation, we reach almost 80 %. All these causes are attributable to human activity. A particularly noteworthy case is that of bees, which are suffering from the almost indiscriminate use of a family of insecticides that has been very effective and widely used for some years: neonicotinoids (what a curious coincidence with the harmful tobacco, right?).

What about mosquitoes - annoying and dangerous - when they transmit diseases? It's clear that most people don't want them around. But there is one thing to keep in mind: not everything we see flying around us is annoying or dangerous. On the contrary, only a tiny part of insects is dangerous, since most of them contribute to the reproduction of the plants we need, because they pollinate them, or are part of the food chain that most of the time has something to do with humans. This is the case of bees, and not only of the honey bee, which almost everyone "recognizes" as allies -important allies- for their pollination work. But there are other "services". We have been obtaining products from some of them for a long time: waxes, silk and lacquers.

The genetic underpinnings have been investigated mainly in the vinegar fly (or common fruit fly), which sometimes flies around our kitchens. In agriculture there are thousands of insects that are dangerous or harmful, but others are beneficial when we use them - biological control - as predators or parasites of the previous ones. There are even some that participate in the important work of nutrient recycling, especially in the soil, source of all terrestrial life.

Last but not least, they are part of the incredible and diverse network of animals (what we call animal biodiversity) that eat or are eaten all over our planet: no less than 70% of the known animal species are insects. The ants in a well-preserved rainforest, all together, weigh far more than all the large animals that live in it, including birds and mammals. Without ants, the beautiful poison dart frogs would not be poisonous, nor would they even exist.