Hawaii does have one species of scorpion living here called the Lesser Brown Scorpion. It is not very large but it does pack a punch approximately equal to the sting you might receive from a yellow jacket. For the average person the sting itself will be very intense for a few minutes and moderate to severe localized swell of the area is likely to occur. Beyond that however the damage will be short-lived and all should return to normal within 24 hours. If you are allergic to the sting however that is another story and you should get some medical assistance right away.
These insects are not easily seen and the fact is that many people who have even lived in Hawaii for 10 years and longer have never even seen one. They like to live at ground level under the protection of dead tree limbs and refuse that can hide them from view. It is at night time when they move from their positions and begin their hunting. The will eat any one of a number of insects and will even attack small rodents. Similar to some other insects, they give live birth to the young ones and after mating they will often eat their mate. They have also been known to eat their own babies as well.