The aqir were an ancient insectoid race, created by the Old Gods and obsessed with eradicating all non-insectoid life. They were eventually defeated by the trolls, and split into the nerubians, qiraji, and mantid.
According to a journal entry by Brann Bronzebeard, titan records suggest that the Old Gods created the aqir out of something that was not the silithid or generic insects (as those are descended from the aqir). It was some kind of species of various "proto-insectoid humanoids" that was a part of the "Black Empire." Their civilization, Azj'Aqir, was built in the southeastern deserts of old Kalimdor, and for thousands of years the expansionistic aqir did battle with the other two major civilizations of the age: the ancient Gurubashi and Amani empires of the trolls.
Approximately 16,000 years ago, the trolls finally succeeded in winning a victory of attrition, and the empire of Azj'Aqir was shattered and split. One group of aqir headed north, where they happened upon a titan facility in what would one day become Northrend. They overthrew the tol'vir attendants within, and from the ruins they founded the empire of Azjol-Nerub. Over time, this group of aqir evolved into what are now the nerubians. Another group of aqir retreated south; they too found and took over a titan facility, rechristening their new empire Ahn'Qiraj and eventually evolving into the qiraji. A third group of aqir became the mantid in what would one day become Pandaria.