Horseshoe crabs are not real crabs, but more closely related to spiders or scorpions. The horseshoe crabs have been swimming in the Earth's waters for 400 million years. Although they are not in the endangered species list, their numbers are dropping to be in the extinction list. City University of Hong Kong has conducted a study on the horseshoe crabs in Hong Kong. the result shows that nowadays only 1 or 2 crabs can be found in every , a decrease of 90% in four years when compared to 10 to 20 in 2002.