Starting as an embryo, it only takes a matter of weeks for horseshoe crabs to become small larvae, and then they grow quickly to become juvenile horseshoe crabs. At this point the juveniles are large enough to defend themselves and hunt for themselves well enough to make it to adulthood. Horseshoe crabs grow 33% larger with every molt until they reach adulthood, averaging out at two feet, female horseshoe crabs are larger than males. They are mainly found in shallow waters with soft ocean floors in the Atlantic Ocean. Horseshoe crabs diet mainly consists of mollusks, worms and crustaceans; other than humans the only animals that really prey on them are sharks and sea turtles. Horseshoe crabs have very basic biology, they have been around a long time and know what they need to stay alive. The formaldehyde used to sanitize the animals for dissection did a number on our horseshoe crabs delicate insides.