You should definitely try to get it to eat earthworms; they're hands down the best staple for newts because they are packed with nutrients like calcium, which will fortify your newt. When my fire belly doesnt eat I try with tweezers a few times. Then I take him out of his tank and set him on a damp paper towel and put a piece of earthworm in front of him. He will usually go for it then. If this doesn't work, try putting some pieces of worm on a paper towel on a rock or in a dish (basically anywhere they won't be able to foul the water) and leave them with the newt for a couple of hours. If possible, try to turn off the lights and make as little noise as possible to minimize the stress he/she is experiencing. Hopefully your newt will eat the worm when he isn't under pressure and stress that a feeding situation can cause. Make sure the pieces are smaller enough for your newt to eat; bigger worms intimidate my newt so this is probably the case for yours. Best of luck!