Oregon Department of Agriculture guides
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Start here: Slug or Snail? 

Slugs have: 
  • no visible shell or a small shell that cannot contain their body.
Slug with no visible shell
Slug with small shell covering the end of its tail
Continue to slugs
Snails have:
  • a coiled shell that can contain most or all of their body.
Two snails with shells that can contain most or all of their  body
Continue to snails
 

Slugs

Parts of a slug

Diagram of a slug showing external body parts. These are the body, caudal pore, mantle, pneumostome, tentacles, tubercles, and foot fringe
Slug with the keel highlighted
Slug with an external shell highlighted

Common slug identification key

Start here:

  • Slug has a visible shell - Testacella haliotidea, earshell slug
Picture
Testacella haliotidea, earshell slug
  • Slug has no visible shell and has...

... pneumostome in anterior half of mantle - 
go to "Slugs with anterior pneumostomes"
Slug mantle with pneumostome in the anterior position
...pneumostome in middle or posterior half of mantle -
​go to "Slugs with posterior pneumostomes"
Slug with pneumostome in posterior position

Slugs with anterior pneumostomes

1. No line where tail can be shed. Caudal pore present. Body tubercles uneven, ovoid in shape with no apparent pattern. 
Picture
Arion, roundback slugs
2. ​Line where tail can be shed (can be difficult to see). This can be an impressed line or indicated by a change in the skin texture. No caudal pore. Body tubercles typically diamond shaped in diagonal rows. 
Picture
Prophysaon, tail droppers

Slugs with posterior pneumostomes

1. With bands or spots and...
...foot fringe with vertical stripes, mantle without wrinkles -
​Ariolimax columbianus
Picture
Ariolimax columbianus
...foot fringe without stripes, mantle with wrinkles - 
Ambigolimax, Limacus, and Limax.
Picture
Ambigolimax valentiana
Picture
Limacus flavus
Picture
Limax maximus

2. No bands or spots (may have pigmented speckles) and...
...mantle pointed posteriorly. Body long and worm-like - 
Boettgerilla pallens. 

Picture
Boettgerilla pallens
...mantle rounded posteriorly. Body of typical slug proportions. Go to 3. 
Slug mantle with rounded posterior margin

3. Mantle with wrinkles centered on pneumostome. Keel 1/3 tail length or less - Deroceras sp.

​
Picture
Deroceras sp.
Mantle without wrinkles, smooth or bumpy. Keel from tip of tail to mantle or nearly so (can be difficult to see). Go to 4. 


4. Mantle appearance...
...with U-shaped groove. Foot fringe without vertical stripes. Less than 70mm (2.75”) - Milax gigates

Picture
Milax gigates
...without U-shaped groove. Foot fringe with vertical stripes. Adults over 180mm (7”) - Ariolimax columbianus

Picture
Ariolimax columbianus
​
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