The damage they do is insidious. After seeing enough infected corals, it becomes easy to tell acropora with red bugs. Chadfarmer noticed mine after seeing them enough times and I've learned to spot the telltale signs as well. The damage occurs slowly as color fades with PE lessening, then you might see some coral deaths. Next thing you know, WHAMMO!
Glad you found them, John and hope others will learn to dip all their acquisitions and perhaps even set up a QT tank to observe for other worse pests like acropora eating flatworms and their eggs, montipora eating nudibranchs and their eggs, etc, etc. There are some good dip protocols for new arrivals that are quite easy to follow and cheap too. QT is extra insurance, but I haven't setup a tank for that yet either, which is gambling with some of the worse pests I know.