[Limax maximus,
the giant Garden slug, from Dyers Bay on the Bruce Peninsula]
Limax maximus from Dyers Bay, photo by Aleta Karstad.

The Bishops Mills Natural History Centre is working with others interested in introduced slugs and snails to document these species in Canada (see http://mollus.ca/ ). We're co-operating with a European team that's revising the family to which Limax belongs, and which finds that Canada is the only country where Limax has been introduced from which they don't have samples. If you're going to look for them, go out at night, especially when it has rained or the ground is damp, since they often spend the day well underground, where they can't be found by simply turning superficial cover objects. Pictures, accounts, or specimens may be sent to the Bishops Mills Natural History Centre, RR#2 Oxford Station, Ontario, Canada K0G 1T0, (613)258-3107.

Contact us by phone at (613)258-3107
or e-mail bckcdb@istar.ca

return to Projects

Pinicola home

About us

Bishops Mills
Natural History

Giant Garden Slugs around Dyers Bay and around Ontario

(modified from an announcement in the Tobermory Press, F.W. Schueler, last modied 17 July 2009)

What may be the northernmost Ontario population of a giant slug has been found on the Bruce Peninsula on the slope of the Niagara Escarpment above the settlement of Dyers Bay, by a team from the Bishops Mills Natural History Centre.

Almost all of the slugs that live around houses and in Canadian gardens are introduced from Europe, and many of these are only hardy enough to live in southern Ontario and the warmer parts of British Columbia. One of these species is Limax maximus, the Giant Garden Slug, which is 10-20 cm long, brownish and heavily spotted with black or dark brown.

This species lives in gardens, along roads, in wooded areas adjacent to human settlement, and on waste ground and other disturbed habitats. It is probably native to the Mediterranean region, but is now widespread in Europe. There are places in southern Ontario where this species is common, but in Ottawa it is believed that introductions are killed off by winter cold, though some may survive near heated buildings.

In 1990, when he was working on a survey of the amphibians and reptiles of the Peninsula, Fred Schueler saw one of these slugs in the woods above the settlement of Dyer Bay.

After a thunderstorm on the evening of 23 August 2008, Fred and Judy Courteau walked the Dyer Bay Road, through an escarpment slope forest between the Bruce Trail and the settlement. This was part of an expedition across southern Ontario trying to refind old records of introduced snails and slugs. They found two Limax maximus on the roadside and on the trunk of a Birch tree. This confirms that the species has persisted here, away from buildings, for 18 years. These slugs seek shelter during the day under debris, stones, wood and vegetation and emerge to feed at night and during wet weather. They eat mostly dead vegetation and fungi, but roots, fruit and leafy crops form a small part of their diet. Deep snow, and access to hibernation refuges among broken rock may explain their long-term survival here, at the latitude of Ottawa.

Afterwards, Fred & Judy spoke to Craig Arthurs, who lives in Dyers Bay, and he said that they see big striped slugs similar to these occasionally on the Georgian Bay beach below the Escarpment. He particularly recalls one about 15 years ago which was on the patio of their cottage, and attracted the attention of his children.

Since then, we've received a number of records of these slugs from the Bruce Peninsula, Toronto, and Peterborough, and old records from the Thousand Islands region.

The best characters for Limax maximus in the field would be a roughness of the body (behind the mantle) in longitudinal ridges broken up into what are called tubercles. The mantle (front part of body) is smooth, sometimes with subtle fingerprint-like whorls. Slugs of the genus Arion also have this characteristic, but the tubercles are more sharply defined (raised) in Limax maximus. The difference between Limax maximus and all Arions (besides the extreme size of the Limax adults) is the keeled tail - visible in all sizes of Limax maximus - the keel begins to rise from about halfway down the back, and becomes more compressed laterally toward the tip. The pattern of dark Leopard spots, arranged in rows on a tan body, is most prominent on adults - may not be noticeable on juveniles - but is sometimes absent on adults, sometimes also with colour variation. The one in the photo has very prominent classic spot/stripe pattern.