Human:
A mammal that ranges in size from about 1 to 2 metres.
Weighs between 30kg and 100kg. Females are pregnant for 9 months.
Omnivorous diet. Population estimated around 7 billion.
Ant:
An insect that ranges in size from about 0.01 to 3 centimetres.
Weighs between 0.001mg and 1g. Can produce eggs endlessly given there is an ample sperm reservoir.
Omnivorous diet. Population estimated around 1 quintillion (1 billion times 1 billion).
(from The Encyclopaedia of Relative and Absolute Knowledge by Bernard Werber)