particularly in north america, some "deroceras laeve" grow large enough that they closely resemble "d. invadens". a useful clue to distinguish them is the profile of the end of the tail when the animal has been disturbed or is preserved. the tail of "d. invadens" usually slants vertically upward from the sole for a short distance, or even bends backwards. the tail of "d. laeve" slopes forward above the sole. also, the tail of "d. invadens" is longer than the mantle, whereas it is the same length or shorter in "d. laeve".