Another point I may not have made firmly enough - sometimes when you do something in the exterminator vein, you get close enough to the nest to stir them up, but not close enough to do enough damage. The ants then start to migrate (to somewhere nicer and less pestified) and you're thinking, what a lousy pesticide company, the problem is now worse than ever.
This is especially a problem with spiders, which don't take kindly to most insecticides, because spiders aren't insects, they're arachnids and have book lungs as well as the usual insect spiracle breathing apparatus. Book lungs mean that spiders can even live underwater, for a week at a time... spraying spiders generally doesn't kill them, it just makes them cranky, with a headache. Unless you drown them in it, and even THEN it can take half an hour or more. And with our funnelweb spiders, I don't want to make them any crankier than they are. I see one, I don't spray. I reach for a heavy shoe instead.
So yes, let the exterminator know about the sudden attack of ants and do ask if this could have come about BECAUSE of his recent visit. Certainly you shouldn't have problems again so soon, unless he got the nest with a near miss.
We no longer use pesticide companies. Long story. And that's just us. We get by - but then, we have a pet house spider called Charlotte, whose web is in the corner of the kitchen window. Whenever her web area is getting too ambitious, I clean a lot of it away, but I always leave a corner near the pitcher plant and the drosera for her, she keeps the flies down.
Marg