Follow Up:

Well, I went digging. I found 1 bulb that was just late and 2 baby bulbs that weren't connected to anything with a single leaf on each. Should have been about 3 - 4 adult bulbs... No idea what happened. No tunnels evident. No evidence of rotted bulbs though I suppose it would depend on the degree of decomp. Anyone have any ideas? Should I bother trying to replace them? They're supposed to be quite perennial...

I grow Daydream and it is one of my favorite tulips. I find that they are more perennial than most tulips, but still, they start weakening after two or three years. 50% return for the third season isn't bad for a tulip.

Based on what you found when you dug them up, it sounds like they divided into weak baby bulbs. This is typical and happens to all tulips sooner or later when they are grown in a climate that isn't native to them. Plant more, though, they are beautiful and it's worth it :)

Maybe you dug into them during the summer while planting something else?

Usually if tulips go missing, something ate them. If they are just producing alot of leaves it's dividing they need. They are trouble, but worth it I think!

I've noticed my other tulips getting more plentiful but smaller and figure they've been dividing, but these are the only ones (knock on wood) to leave a bare spot. I didn't plant anything else along that line so I know I didn't slice them, but I think I'll break down and get some more this fall. They are kind of special. :-)