depending on the ant, you can use teetree oil! this is what I use and it works like a charm, just circle your terrarium and the edges, ALL the egdes with it every day to every few days, the ants wont cross it becasue it messes with their "sensors" also any chili oil will I think work as well. if you want to see this trick really work get an ant on the counter and draw a circle around it with the oil. they just start freaking out and wont cross it. once agian I dont know what kind of ants you have, for me this works with sugar ants, if you have carpenters you may have a much bigger problem!