New (Picky) Long Toed Salamander: Worm Problems

I recently inherited "Junior", an Ambystoma macrodactylum, and he/she was raised on slugs and caterpillars for a little over 8 years. I am trying to switch to a more earthworm-centric diet, but I ran into a dilemma. When I cut the earthworms to palatable sizes, the salamander consistently refuses to eat them (this has happened several times).

I was trying it again tonight, but I accidentally dropped the longer ~1.5" worm segment into the tank. To my surprise, the salamander ran out of its burrow, dragged the worm back into it, and chomped it down.

Junior ran over to beg for more, so I gave him a small, appropriately-sized piece. Complete rejection. On a gamble, I offered another longer-than-recommended (but not as long as the first) worm piece. That one was eaten with gusto.

Does anybody have a suggestion(s) on how to break this unhealthy eating habit, before I end up with a choking incident?

In addition to the problem of Junior only eating worms that are too big, he/she likes rubbing them in the dirt before proceeding to "slurp" them. How worried should I be about compaction, since the worms still have some dirt on them when they get swallowed?

What type of worms are they? Some worms give off a funky smell (and presumably taste) when cut. Try Canadian nightcrawlers.

The dirt is unlikely to cause problems. If Junior isn't shy, you could feed him/her in a separate container.

I think the worms are just regular earthworms, only a few inches long. Not quite the size of full-blown, post-rain nightcrawlers.

If it helps, here's a picture of what they look like--maybe they're red wrigglers? That would explain a lot, even though the ones I cut didn't seem to smell bad.

http://environmentprogress.com/wp-content/uploads/2013/02/KHR_nano-earthworm.jpg

Junior is still pretty shy, so right now I'm considering putting some plastic wrap or a piece of foil in front of the burrow where I put the worm, or even burying a bottle cap.

Thank you very much for your help/reply!