Associative learning by C. elegans is variable when butanone is paired with starvation

The nematode <i>C. elegans</i> has been reported to show a reduction in its preference for the odorant butanone after prior exposure to butanone coupled with starvation. Here we report unexplained variability in such associative learning. Pre-exposure of unfed worms to butanone resulted in different responses during different trials of subsequent chemotaxis assays - from strong avoidance to enhanced attraction. Given this variation in associative learning despite the artificially controlled lab setting, we speculate that in dynamic natural environments such learning might be rare and highlight the challenge in discovering evolutionarily selected mechanisms that could underlie learning in the wild.