Ambigolimax valentianus Another Alien Benefactor of Milder Winters

 

A group of Ambigolimax valentianus found in the garden behind a hanging basket

Recently I took a large trough like hanging basket down for the winter which I fix onto the garage wall for pollinating insects. I knew this would likely have some treats behind it to photograph, and whilst I was hoping for some spiders I found a numerous group of the slug Ambigolimax valentianus a species strangely I have not recorded in my garden before. Also known as the Iberian Three Banded Slug, Ambigolimax valentianus is native to the Iberian peninsula and has spread widely around the world, where across much of its alien range is considered a pest species. 

Introduced with horticulture, this species initially was only found in heated greenhouses in Britain, until around the 1980's when it first began to be found outside. This was due to our cold winter temperatures, the species is now regularly found in gardens and appears to now survive our milder winters well. Now this species is regularly recorded outside in synanthropic (in association with humans) habitats, particularly gardens. 

This species can overpopulate rapidly and cause problems for gardeners and horticulturalists especially when confined in greenhouses.  Although a species which has a preference for warmer conditions, its eggs strangely fail to survive consistent temperatures above 33oC, likely resulting in it being found in cooler stream sides, cellars and caves in its native range. 

This species feeds on a range of plants as well as algae on rocks and windows. It is relatively widespread in Britain and common in Yorkshire, it is strange I have never recorded it in the garden up until now, likely to be an oversight. The slugs in the photo were tucked away between the felt from the hanging basket and the wall, likely emerging at night to feed on the plants. Interestingly I removed the basket late in the afternoon and many of the slugs did not disperse until the following morning as the temperature increased. The compost heap is likely to support more of these individuals, so warrants a further look.