Hornets are the largest eusocial wasps; some species can reach up to 5.5 cm (2.2 in) in length. The true hornets make up the genus Vespa and are distinguished from other vespines by the width of the vertex (part of the head behind the eyes), which is proportionally larger in Vespa and by the anteriorly rounded gasters (the section of the abdomen behind the wasp waist). The best known species is the European hornet (Vespa crabro), about 2-3 cm in length, widely distributed throughout Europe, Russia, and Northeast Asia. In Vespa crabro, the nest is founded in spring by a fertilized female known as the queen. She generally selects sheltered places like dark hollow tree trunks. She first builds a series of cells (up to 50) out of chewed tree bark. The cells are arranged in horizontal layers named combs, each cell being vertical and closed at the top. An egg is then laid in each cell. After 58 days, the egg hatches, and in the next two weeks, the larva undergoes its five stages.