Summary: Southern insects cross the Alps
In the course of the last 10 to 15 years more and more southern thermophilous species have been sited in central Europe. In particular, warmer winters enable numerous thermophilous species to expand their ranges north of the Alps.
This high and large mountain area meters constitutes a strong barrier for the dispersal of plant and animal species between southern and central Europe. Several butterfly species, however, regularely invade central Europe from southern Europe or even Africa.
The most important gateway to central Europe for southern insects species are the Burgundian gate, the Danube valley and the northern German lowlands. Although, the Alps act as a barrier, they nevertheless can be circumpassed from west and east.
Also, shipping from overseas and other traffic by water, land and air may enhance the introduction of species from warmer regions.