In terms of body mass, the Etruscan shrew is the smallest mammal on Earth. They weigh 1.8 grams (0,06 ounces), making each individual shrew roughly as heavy as a playing card. They may be tiny and incredibly light, but Etruscan shrews have a serious appetite. On an average day, each shrew can eat twice its own body weight in insects – the greedy rodents are able to eat so much due to their lightning-fast metabolism. For its size, the Etruscan shrew is also a fearless hunter, using its whiskers to detect prey equal in size to its own body, then taking it down before it makes a single evasive move.

Of course, being so small means these shrews are in danger of being eaten themselves. Darting in and out of cover is required to avoid being caught by predators.
Size: 40mm (1.6 in)
Comparison: The size of a matchstick