These jellyfish are not particularly big, nor are they as venomous as many of their kin, yet their victims are believed to number in the tens of thousands every year. The high sting rate is largely down to their sheer numbers. During the summer months, huge blooms converge in inlets such as Chesapeake Bay, which are popular with swimmers. A live prediction map has been created by the National Oceanic and Atmospheric Administration (NOAA) to help avoid them.
DANGER FACTOR: In the majority of cases, it only causes a temporary rash, although other species of sea nettle can have more severe effects.
Bell diameter: 20cm (8in)
Tentacle length: <50cm (20in)