Ambigolimax valentianus (also known as Lehmannia valentiana) is a species of terrestrial slug, a pulmonate gastropod mollusc in the family Limacidae.

External appearance does not reliably distinguish Ambigolimax valentianus from other members of the genus, such as A. parvipenis, with which it may co-occur.

[8] This might cause confusion with A. parvipenis but the penis of A. valentianus without the appendage is about as long as the bursa copulatrix and its duct, whereas it is only about half the length in A.

[7][12] In more temperate parts of Japan, the life cycle is similar, but shifted two months earlier, so that slugs mature already by August or September and die by May.

[15] Ambigolimax valentianus eats green leaves and shoots,[7] and consequently can be a pest in greenhouses[16] or even outdoors.

[18] This species seldom climbs up trees and during the day is most commonly found under boards, rocks and plant containers.

[19][8] Often its first discovery in a country has been in greenhouses, from whence it has spread to gardens, other synanthropic habitats outdoors, and even to woodland, likely facilitated nowadays by global warming.

[23][19][24] A bizarre consequence of its abundance on Gough Island is that it prevented the eradication of another introduction, the house mouse, by consuming the poison bait dropped from helicopters.

Europe Africa Asia Australasia Americas Oceanic Islands Ambigolimax valentianus has been used as a model species for studying the neuromechanisms of learning and memory, particularly by researchers in Japan.