Btk, or Bacillus thuringiensis kurstaki, is a bacterium commonly used as a biological pesticide. It produces proteins that are toxic to certain insects, particularly caterpillars, making it effective in controlling pests in agriculture. Farmers often apply it to crops to reduce damage from these harmful insects while minimizing the impact on beneficial species. This bacterium is considered safe for humans, animals, and the environment when used as directed. Btk is part of a larger group of Bacillus thuringiensis strains, each targeting different types of pests, and is widely used in organic farming practices for sustainable pest management.