i wash them under water for a copple of secs and mine are eating them!
but every axolotl need to adjust to new food. it can be he never ate it before so just try a copple of days without giving something else.
my white girl also made problems and she didnt want to eat them for over 2 weeks... stobbern girl... now shes like a shark on them XD after a few days i just gave some red worms if she wasnt eating them so she wouldnt get underfed.
you can also chop 1 in little pieces to let it get used to it and put it between the red worms in the hope he'll eat it.
my girl was still spitting it out when i put it between the other worms so dont keep your hopes high
they can be very stobbern sometimes but 1 will win ^^
most of the time they taste the soil where the worms are breed in and they just need to adjust to it.