Yacov Lewin spotted the creatures in the waters of Yowie Bay at Port Hacking around 8.30am today. Mr Lewin said he's never seen anything like it. READ MORE: Box jellyfish have been spotted in Port Hacking.(Supplied) Box jellyfish, named for their body shape, have tentacles covered in biological booby traps known as nematocysts - tiny darts loaded with poison. Their sting can result in paralysis, cardiac arrest, and even death, all within a few minutes of being stung. Box jellyfish are common in Australia all year round however they are most prevalent in the summer months between November and May.