Why Ants Rule the World Count on ants to be the first uninvited
guests to show up at a picnic. Their party-crashing feats show
just how productive and important they are and hint at why they
thrive in just about any habitat. It hasn't always been an ant's
world. Scientists estimate modern-day ants first evolved about
120 million years ago. But the fossil record suggests that ants
at this time weren't the prevalent insect that they are today.
Not until 60 million years later, when some ants adapted to the
new world of flowering plants and diversified their diets, did
the critters achieve ecological dominance. Since then they've
had a successful run of the planet [Image Gallery]. Scientists
estimate that about 20,000 ant species crawl the Earth.
Taxonomists have classified more than 11,000 species, which
account for at least one-third of all insect biomass. The
combined heft of ants in the Brazilian Amazon is about four
times greater than the combined mass of all of the mammals,
birds, reptiles, and amphibians,