Maracas were created and first used by the native indians of Puerto Rico: the Tainos, as a percussion musical instrument. A pair of these are used to create the unique sound so common in Latin American and Puerto Rican music.
Maracas are made from the fruit of the higuera tree so common throughout Puerto Rico. The fruit must be round and small. After taking out the pulp of the fruit through two holes that are bored through the dried shell, small pebbles are introduced into it. Then a handle is fitted to the dry fruit shell. Unequal amount of pebbles are used in a pair that make up the maracas, to produce their distinctive sound.
In salsa music the maracas have become one of the most important percussion instruments because they add a driving pulse in the high frequency spectrum. Perhaps their importance to salsa is like the role of hihat and snare drum in pop and rock music.
Maracas are now often made of new materials, such as plastic, but are used the in same way, fulfill the same musical role in Latin bands, and retain the same distinctive sound.