Check the pH of the soil if you can. Take some of the soil and soak it in a small amount of water and test it with a liquid regent kit. From what I have read acidic soil can cause ruptures and tumor looking injuries.
Too warm can harm them also and I have seen regular earthworms rupture when they get stuck out of the ground and the sun hits them.

38F seems really cold for Europeans also. Everything I have read has the proper temp between 50F and 80F with both ends being extreme and not to be held there for too long.
Raising European Nightcrawlers