Picture of Portuguese Man of War Sting
A Portuguese man of war is a type of jellyfish that has tentacles extending from its base that can be up to 165 feet long. Those tentacles have toxins in them to help them catch prey and can cause painful stings when humans come in contact. Burning painful welts can result and may last for days and even weeks. Strong reactions can see a fever, dizziness, nausea and cramps.
Text Source: UpToDate