I don't know what it is about defrosted bloodworms, but aquatic newts seem to get 'hooked' on them quite easily. By that I mean if you offer nothing but bloodworms for any length of time you'll have a hard time getting them back on to more nutritious foods like earthworms or pellets. My pyrrho's would take defrosted bloodworms over anything else if I let them, even live bloodworms!