I have a vague understanding that ants and moths use pheromones in a variety of ways, but recently after a heavy rain my office is being explored by a some small ants looking for food. They decided it was a potentially interesting area to explore after finding a drink lid that had left on my desk. That the ants left a pheromone trail for other ant's to follow I understand, and after removing the lid, the number of ants has gone down as expected.

However this morning I came in put my Starbuck's (Mocha with an extra pump of chocolate) on my desk and after a couple of minutes saw what appears to be the last remaining little ant climbing up the side of the cup. So my question is:

a) Was the ant just very lucky? Wandering around anyway and encountered the cup? b) Did the ant smell the Mocha/coffee and decided to investigate because it smelled like there was something good in the area?

This led me to wonder how much insects use their sense of smell to find food. I was generally aware that flowers are brightly colored and some patterned in the ultraviolet, and I guess it might be obvious that flowers also might smell good and flies are attracted to rotting flesh etc. I think I also read some time ago Luna Moth's find each other by airborne pheromones and the antenna are very sensitive and they can follow the gradient to find the moth to mate with.

So do ant's find food by smell? How much do non flying insects depend on smell to find food?

Thinking about it, it must be yes, but are there specific 'food' molecules ants are especially responsive to?