Yes, because Betta's are tropical fish, not cold water fish. Only cold water fish should not have heaters otherwise they would literally boil to death. Betta's come from an environment where they live in warm water and they are breed in warm water, so therefore they need to live in warm water. They aren't very adaptable fish and despite what people say, they aren't very tolerant to bad water conditions. People will say otherwise, but they either don't keep Betta's so they don't really know, or they have kept Betta's and they haven't lived that long (meaning less then 5 years). You also must have a filter, all fish must have filters otherwise any toxin or chemicals that get into your tank through the air are likely to kill the fish. Another thing I will mention is that no fish can live in half a gallon of water, it's not enough water for them to swim in, and there will not be enough water for them to get oxygen from. Betta's need a minimum of 5 gallons as they get to be 3-4 inches at adult size, therefore they need approx one gallon of water per one inch of adult fish. It may look like the fish is fine in less the 5 gallons, but they can't talk for you to ask them! It would be the same as an elephant living in your bathroom, a little cruel yeah?