What life stage do heartworms mature into adult worms inside a dog's body?

Heartworms, which are transmitted to dogs primarily through mosquito bites, undergo several developmental stages after entering the dog's body. Once the infective stage, known as the third-stage larva (L3), is injected into the dog, it travels through the tissues and eventually enters the bloodstream. It takes approximately six months for these larvae to mature into adults.

The correct answer focuses on the adult stage because this is the stage during which heartworms become fully developed, capable of reproducing and causing significant health issues for the host dog. In this stage, heartworms can live for several years, leading to complications such as heart failure, lung disease, and other serious conditions. Understanding this life cycle is crucial for effective prevention and treatment strategies for heartworm disease in dogs.