Yes. To feed only one food is like you eating only a hotdog (without the bun and condiments) every day forever. And bloodworms grow up in muddy water that is often laden with runoff heavy metals so, even though they've been dried (or frozen), they will carry that stuff in their tissue and your fish will eat it. A little will be okay for a healthy fish but as an only food, not a good idea. Some fish will even develop an allergic reaction (some fatal) to bloodworms. So get your fish used to eating other foods. And if you can get live food, or frozen fish foods (brine shrimp, bloodworms, glass worms, chopped beef hearts) from your local fish store/pet store, add that to weekly menu. Live food will ignite your fish's hunting instincts and give them something to do (if you want to see your betta at his best, try live food and watch how he attacks it and then does a little victory dance when he's caught it--they practically grin with glee). Just make sure your source for live food is clean (like, if you net out of a pond, just be real careful you aren't introducing bad stuff to your tank/fish).
