The identity of the strange, pea-sized animals - littered along the beaches of Oahu, Honolulu - has also perplexed marine biologists, who have never seen anything like it.
Most of the crabs, which washed up in the surf over the past few days, were dead or dying.
Experts at Waikiki Aquarium believe they may be the larval stages of the 7-11 crab, a crustacean commonly found in the area, but added there has never been an event like this before.
Norton Chan, a biologist at the aquarium, said: 'What you are seeing is a swimming stage, probably a few more molts before they settle into their crab stage self.'
Researchers are said to be studying those which are still alive to try to find out what they will grow to become.
The little crabs are less than an inch long and, if they are 7-11 crabs, they will eventually grow to around six or seven inches.
'The lifeguard called and asked what these things were because she had reports that surfers were actually having these things crawl up on their boards and onto them,' Mr Chan added.
Meanwhile, one resident told KHON news: 'It's really weird.
'It looks like you want to eat it like a berry.'
Another said: 'When something washes up like this, you don't know what to expect - maybe tsunami stuff.'
The coastline affected stretches from Kahala to Ala Moana on the southern tip of Honolulu.
Dr Andrew Rossiter, director of the Waikiki Aquarium, reckoned that the crabs were washed up after rough seas left air bubbles in their shells, leaving them unable to dive.
As a result of this, they get caught up in tides and come ashore.
'It could be a flux of warm or cold water coming in but I don't have any signs of that,' Dr Rossiter told Hawaii News Now.
He added: 'And if it was pollution, it would have affected other species as well, so we really don't know.