Hi,
From what I've picked up on other forums and from books, which isn't much, Atelopus spumarius are one of the easier species of Atelopus to keep. They are native to lower altitudes than many other species of harlequin toads so they do well when kept at temperatures higher than many other species can tolerate. Their over all care is pretty much similar to keeping the larger species of dart frogs. Pretty much all harlequin toads are native to streams and rivers in central american so it would be good to include a streamside with rocks and crevices for females to hide in and males to call from.
These are rare frogs that are not commonly bred in captivity. Wild caught animals are availible from time to time and usually aren't too expensive but from what I've heard they often are in rough shape with a good load of internal parasites to deal with. If you haven't kept any small, delicate frogs before you might want to pass up wild caught Atelopus and first try keeping some captive bred dart frogs. Good luck!
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Devin
devin@amphibiancare.com
www.amphibiancare.com