Gary, Yes this is normal for these guys, and the tubiflex worms are ok.
I miss the ones I had years ago for that very reason.
I fed mine frozen brine shrimp and aquatic frog and tadpole pellets wen they were young.
and when they got larger I would feed an occasional guppy that was suppled by my coworker
in the Science education bldg.
with a staple of frozen krill and shrimp pellets , blood worms.
I had a piar of them started out in a 5 gallon hex as a normal fish setup with power-filter and a airstone
then moved up to a 20 gallon long for the last 4 years I had them.

When I left I gave them to the school and they were well looked after and lived another 4 years.