Does terro ant killer expire?

I bought some terro ant killer about two years ago and it worked really good when i bought and even a year ago when i needed it again it worked, but not ive been using it for two weeks and ants still keep coming and drinking the stuff and wont stop coming. Before when i used it they would stop coming cause they died after about a day i think. Its the liquid kind that you drop onto little pieces of cardboard. I feel like it stopped working and that ive just been feeding the little buggers. Is it possible for it to have stopped working after 2 years? Thanks.