As many as 4,000 eggs may be laid in the nest. Then the male, or males since more than one male often hangs on, fertilizes the eggs as he is dragged behind the female. The water covers the eggs with sand as the female drags on to the next site. The six or seven inches of sand protect the eggs from predators and keep them moist. One female may lay up to 20,000 eggs in one night 90,000 in a year.
Incubation takes anytime between two weeks to months.
The eggs swell to about 2-3 mm and usually break out of their outer layer in a few days. While they are larvae, they molt four times in the egg. Next the young trilobyte larva swims for about six days. It floats on its back and paddles along with its little gill plates. It will continue to grow by shedding its shell.