prey on

prey on or prey upon  {v.}

1. To habitually kill and eat; catch for food.

Cats prey on mice.

2. To capture or take in spoils of war or robbery.

Pirates preyed on American ships in the years just after the Revolutionary War.

3. To cheat; rob.

Gangsters preyed on businesses of many kinds while the sale of liquor was prohibited.

4. To have a tiring and weakening effect on; weaken.

Ill health had preyed on him for years.