According to Harvard biologist ant expert EO Wilson, there are an
estimated 100,000,000,000,000,000 ants in the world.
"EO Wilson , a noted Harvard biologist and expert on ants, estimates
that the number of ants in the world is between ten to the sixteenth
and ten to the seventeen or: 100,000,000,000,000,000 ants."
"Scientists estimate that there are one quadrillion
(1,000,000,000,000,000) ants living on the earth at any given time."
Embery, Joan with Ed Lucaire. Collection of Amazing Animal Facts. 1983.
Number of Ants in the World
The Physics Factbook Edited by Glenn Elert
This related ant question might interest you as well.
"ants in the world"
I hope this is helpful!