Three warm springs used to form a rare desert marshland at the base of the mountains outside Socorro, New Mexico.
Two of these have now been diverted for the town’s water supply and only Sedillo Spring remains as the home of the Socorro isopod (Thermosphaeroma thermophilum), a freshwater species of crustacean resembling pillbugs (a.k.a. rolly-pollies). One can see them swimming among concrete-lined pools, remains of when the spring was used as a spa.
In 1988, an obstruction in the spring’s flow caused the spring to dry up and the isopods to die off. Fortunately, the water flow was restored and the University of New Mexico was able to reestablish a wild isopod population using captive specimens. Today, captive populations are kept by a number of agencies that ensure the species’ survival in the event of another extinction in the wild.
The trail to Sedillo Spring is accessible only on foot or by bike. The site is on private property but the owner allows people to visit the spring. Please do not disturb the isopods by entering the water – it is their only home left.
Know Before You Go
The Socorro Isopod - Sedillo Springs trail runs west of Socorro to the base of the mountains.