No they don't have to eat crickets. Many people prefer Dubia roaches and other types of roaches over crickets because crickets smell! You can feed moths, dragon flies, mantis, silkworms, superworms, phoenix worms, hornworms, grasshoppers, katydids.etc. Many of these have to be caught of course. My chameleons love dragon flies, but I cannot catch them too often. Crickets are just used because they are readily available and easy to gutload. Basically variety is key. They can exist on one feeder, but down the road that is going to cause problems for them from lack of nutrition. They need a varied diet, where they get different nutrients from different prey items.