What kind of insect eats tile grout?
Answers:
none. Your grout is probably getting destroyed by mold, and the insect is eating the mold
Other answers:
Dry grout termites.
Dry grout termites.
It would be easier to just scrape it out with a hard instrument.
Cement mites.............. this is the same as snipe hunting. Have a great day
I don't know if they eat grout, but I know ants will bore through it. When we regrouted and tiled my folks pool, we had problems with them boring through the wet grout...we put insecticide in the mortar and remixed and reapplied. We thought all was well, but they actually were able to bore through the dry grout weeks later and they reappeared in their favorite spot. We were truly surprised by their tenacity and by how fast they can move the grout! Now even years later, they are still busy in their tunnels, although now that they've got their tunnels dug through the grout, they seem happy to not be removing more than what we can all live with.
Are your tile munchers inside or outside?
It is possible that your tile grout was done improperly. If it was installed with too much water the grout will actually just gradually powder out into dust.
A good way to kinda tell if this is the case is the grout colors would be a little off or spotty. Also it may appear lighter than the color you originally selected.