Why do some animals have poisonous or toxic glands?

Some animals have poisonous or toxic glands as a defense mechanism or to subdue their prey. For example, certain species of frogs, snakes, and insects produce toxins that can deter predators, making them unpalatable or dangerous to eat. These toxins are either injected through bites or stings, or in the case of frogs, absorbed through the skin. The presence of poison or toxins is often an evolutionary adaptation that improves survival chances, either by deterring predators or incapacitating prey.