I also emailed Bill Nuttley, a neurobiologist whose specialty is the nematode worm C. elegans, and asked him whether blocking had been confirmed or disconfirmed in this worm. I received the following reply (Nuttley, personal email, 18 July 2003):
As far as I have heard, the jury is still out, whether there is blocking, although those that have found it still claim that there is no dispute about their data. There are a few finds, but alternative explanations have not been ruled out, yet. So far, blocking, if it is there, is definitely not as universal and general as in vertebrates, at the least.
As for blocking, a student has been looking at that and although the trends are all encouraging and the data looks pretty good, we fall just short of making stats. A few changes to the protocol and I think we will be able to demonstrate blocking, but so far no.