vespa velutina

A hornet introduced from Asia that has spread throughout mainland Portugal. It is larger than a wasp, with a black thorax and yellow-tipped legs; the nest is a grey ball, often high up in a tree, but it can also be under a roof, on a balcony or in a wall. It stings when you get close to the nest; the venom is not deadly in itself — the danger is a severe allergic reaction. Nests are at their largest in autumn, which is also when stings are most common: during the grape harvest and in gardens and orchards.