This paper reports results of laboratory experiments to evaluate the cold hardiness of the terrestrial slug, Deroceras reticulatum . The mean supercooling point (SCP) rose from -4.2� C in summer to -3.6�C in winter. The SCP that caused 50% mortality (LSCP50 ) remained constant at -4.7 to -4.8�C in both seasons, but slugs were able to survive the frozen state for longer in winter (LD50 of 31.8 minutes compared with 17.0 minutes in summer). Slug survival at freezing temperatures was prolonged to at least five hours when placed on a moist, absorbent substrate. D. reticulatum exhibits partial freeze tolerance, with an increased survival in winter. The results are discussed in relation to the slugs' natural environment.
http://www.ingentaconnect.com/content/cryo/cry o/2004/00000025/00000003/art00005
Well that's what google said when I entered 'frozen slugs' anyway! ;0)