Naphthalene sublimes easily because it has a low triple point. A substance's triple point is the temperature and pressure at which it can exist in all three phases of matter: solid, liquid and gas. Under ordinary atmospheric pressure, naphthalene's triple point is 176 degrees Fahrenheit.
Naphthalene is the active ingredient in mothballs. The ease with which it sublimes is what makes it an effective insecticide. In gas form, it both poisons and suffocates insects. Gaseous naphthalene is able to penetrate clothes and fill small spaces such as chests and closets.
Naphthalene's low triple point means it has a low persistence in the environment when exposed to air. It sublimes into gas and dissipates into the atmosphere. When conditions trap naphthalene in soil or an enclosed space, or otherwise prevent it from sublimating into open air and dispersing, it can persist for longer periods of time.
Naphthalene is also an effective insecticide on crops, as well as an animal repellent. Naphthalene is a popular deterrent for snakes, rabbits, squirrels and bats. It works on these larger animals by the same mechanisms it uses to kill insects: toxicity and suffocation.
Naphthalene should be used with caution as it is also toxic to humans and pets. Common signs of exposure to naphthalene include vomiting, dizziness and headaches.