A population of snails is separated when an eight-lane highway is built. After 50 years, the two separate populations can no longer interbreed. This describes the process of

All fly species have shortened hindwings called halteres. These don't generate useful lift, but are used as sensory organs for balance to help stabilise the insect while in flight. A group of flies known as Calyptratae, which includes houseflies and blowflies, rhythmically move these wings when standing.