Of all the ant sites on the internet, few are as effective an outreach tool as AntWeb.org’s excellent Ant Blog. Reader questions about everything from ant-rearing tips to identifications to pest control are farmed out to the appropriate experts. Responses are characteristically authoritative and good-natured. Consider the Ant Blog’s answer to the above question about patio ants:
…many ants regularly relocate their nests on their own, and it turns out that this behavior has been previously studied in Formica subsericea (Smallwood 1982 – full citation below). According to Smallwood (1982), Formica subsericea change nest sites about every 90 days. So if you wait long enough, they may leave on their own, though they could be replaced by yet another colony. Hoelldobler and Wilson have a section on ant nest relocation on page 171 of their 1990 book, “The Ants”. They discuss a number of factors that are known to motivate some ants to relocate their nests including mechanical nest disturbance, flooding, competition, and predation. I doubt you want to prey on these ants but, given enough disturbance, they may choose to leave on their own. Digging up your old patio may be all the motivation the ants need to leave.
Ant Blog is a valuable service, performed entirely for free. Contact firstname.lastname@example.org with your questions.