Ants represent one of the most evolutionarily and ecologically successful groups of animals. The 120 million years of history and their complex sociality led ants to their high diversity, with more than 13,000 species described. The real number is probably much higher, maybe 20,000 or even 30,000 species.
Ant species richness mostly follows a latitudinal gradient, with more species occurring toward the equator. Around 600 ant species are present in Europe and every year many new species are discovered. Here, a higher number of species can be found in particular biogeographical and evolutionary areas: the Balkan, Iberian and Italian peninsula. Other types of areas such as islands (e.g. Crete and Sicily) also shown a high number of species and endemisms.

Ants play key roles in most terrestrial ecosystems. Although they reach the most astonishing biomass value in equatorial forests, they have a strong impact in temperate regions too, from forests to agricultural lands and even cities: they are among the most abundant generalist predators of other arthropods (sometimes controlling key pests), affect the soil quality through digging and cycling nutrients, disperse the seeds of several native plant species while consuming those of others, and they may be involved in complex mutualistic relationships with several other insect groups, as well as plants and fungi. Finally, they are also themselves the food of many among vertebrates and invertebrates!

We can’t think of ants without thinking about their social behaviour on which their success is rooted. Ants have been a fascinating model for generations of scientists describing their complex social structure, communication system, foraging strategies, and so on.
European ants exhibit very diverse social systems, some living in monogynous groups of a few dozens and others in supercolonies of tens of millions with hundreds of queens. Some are social parasites, usurping the colonies of other species to found their own, simply acting as uninvited guests (inquilines), or even becoming slave-makers. There are ants that never leave the canopy of the highest trees and those who never emerge from the soil or from caverns to see the sunlight, those that fiercely bite, sting or spray toxic substances to their enemies, others that deceive predators by mimicking more aggressive ants and even some that flee adopting the shape of a ball with their body and rolling away. Phylogenetic patterns leading to this diversity of adaptations are yet to be documented in most cases.