First of all, most axolotls love them and they are the perfect size (about 3" long) for an axolotl to eat. Whereas Canadian Nightcrawlers are usually too HUGE making it hard for the axolotl to eat them and Canadian Nightcrawlers are expensive buying them by the dozen at your local bait store.
Secondly, they provide good protein-based nutrition to your axolotl. Especially when the worms are raised like we raise them here at the Mottled Lotl.
Thirdly, they are hearty and survive even in low-level composted food environments. If you have been using salmon pellets to feed your axolotl that is great, but you may be discovering how much it makes the water murky and forces you to do clean water changes more often. Simply put, European Nightcrawlers are easier to care for, easier to handle, easy to reproduce, less messy than salmon pellets and axolotls eat them more readily than any other worm.
Fourth reason is because all of our worms are all fed our exclusive homemade worm feed with specially-formulated alfalfa, oatmeal, and vitamins galore which produces a worm with higher nutritional value to your axolotl.
We have the BEST European Night Crawlers available for axolotl food here