Horseshoe crabs don't usually reproduce in captivity. They have in Sioux Falls.

The Great Plains Zoo & Aquarium has welcomed the rare hatching of more than 1,000 horseshoe crabs at the Butterfly House & Aquarium , according to a Tuesday morning press release .

More: Butterfly House to eventually move to Great Plains Zoo; merger announced

This phenomenon is quite atypical, given horseshoe crabs don’t generally reproduce in a fully submerged aquarium setting. In the wild, however, they can lay up to 4,000 eggs on sandy beaches, according to the Great Plains Zoo & Aquarium press release. Horseshoe crabs can usually be found from the Gulf of Maine all the way down to Florida, according to the Great Plains Zoo & Aquarium’s website .

More: Great Plains Zoo welcomes new giraffe, meerkats to Sioux Falls

Horseshoe crab hatchings, unfortunately, rarely reach adulthood with about a 0.01% chance due to natural predators. Even if wild horseshoe crabs surpass all odds and fully mature, their population is on a steady decline because of overharvesting and habitat destruction.

An aquarist made this discovery during a routine water change in the Eastern Shores exhibit , a newly developed “touch pool featuring diverse species.”  The trilobite larvae, or baby horseshoe crabs, were carefully sifted from the exhibit's sand and relocated to a tank with warmer water and reduced salinity, conditions that better simulate waters where they would naturally hatch.

While Eastern Shores mimic the colder, saltier waters favored by adult horseshoe crabs, many of the more than 1,000 hatchlings might not survive their first molt. Nonetheless, hundreds have successfully reached this initial stage and continue to grow, although they will undergo several more molts before reaching maturity.

“Finding and raising baby horseshoe crabs is a surprise for the aquarium team at the Butterfly House & Aquarium and such a unique opportunity for growth,”  said Michelle Coley, the Aquarium & Conservatory Director and Marine Animal Specialist. “ Not only does the staff get to learn new skills in rearing aquatic animals, but the knowledge and information gained from this experience will be able to be shared and exchanged with other zoos and aquariums around the world. Since horseshoe crab populations are on the decline due to over-harvesting and habitat destruction, zoos and aquariums have a unique opportunity to assist with helping wild populations of horseshoe crabs by raising this species in human care.”

For now, the hatchlings are being cared for behind the scenes at the Butterly House & Aquarium . While they are not on public display, updates on their progress will be shared on social media .

More: Sioux Falls businesses are starting to offer sensory-inclusive opportunities

Visitors can view adult horseshoe crabs from 10 a.m. to 1 p.m. Thursday through Sunday at the Eastern Shores exhibit. Tickets can be purchased online or in person.

“The Butterfly House & Aquarium staff is excited to continue to create a strong network within the zoo and aquarium community of shared knowledge and experience, so that we may assist in the preservation and conservation of vital aquatic habitats and their inhabitants,” Coley said.

This article originally appeared on Sioux Falls Argus Leader: Horseshoe crabs don't usually reproduce in captivity. They have in Sioux Falls.