Pacific banana slug

Appearance

This robust slug can attain a length of 185 to 260 mm and may weigh up to 72 g at maturity. This species is normally yellow in color; however, several color morphs exists, that range from white to tan-green, red-brown, brown-green, olive green, slate green and ochre yellow. The mantle and body of the slug is usually of uniform color; however, the mantle in any of the color morphs may possess dark-brown to black spots, while the body remains a uniform color. In some specimens, this pattern is reversed and the body possess spots that are not present on the mantle. In some specimens, the black blotches occur simultaneously on the mantle and body and may even coalesce to give the slug a solid black. The juveniles of this species are finely speckled. This slug has a caudal mucus pore with the pneumostome ( breathing pore) located behind the midpoint of the often finely granulated mantle. The keel appears undulating in strongly contracted individuals and does not reach the mantle. The sole of the foot is usually much wider than the body.

Slugs in this genus are similar in appearance; however, they can be separated based on the following genitalic characters:

A. columbianus: The penis permanently evaginated, and the apical portion is rounded/blunt. The retractor muscle is narrow and strap-shaped, and originates on the apex of the penis.

A. californicus (Cooper, 1872): The penis forms a hollow tube and can be completely invaginated. The apical portion of the penis is slender and is 1 to 1 2/3 times the length of the basal portion. The retractor muscle is broadly flabellate, and originates close to the apex of the penis.

A. dolichophallus (Mead, 1943): The penis forms a hollow tube and can be completely invaginated. The apical portion of the penis bears a flagellum that is 2 to 4 times the length of the basal portion. The retractor muscle is narrow and strap-shaped, and the point of origin is not at the apex of the penis. This species may also be aphallic (does not have a penis).
Source: http://idtools.org/id/mollusc/factsheet.php?name=Ariolimax%20columbianus

Naming

The Banana Slug was first given a scientific name in 1851 by Augustus Gould. Columbianus is named after the Columbia River district where this animal was first studied.

Distribution

Limiting abiotic factors such as moisture, temperature, and the need for heavy ground cover make the forest habitats of the west coast the perfect homes for the terrestrial slugs. The Ariolimax columbianus are most likely paleoendemics restricted to a range that extends as far north as Sitka, Alaska, to the west side of the Cascade range in British Columbia, on the west coast of Washington and Oregon, and finally into California, primarily on the coast and as far south as Salinas Valley (Harper 1988). In 1992, The Veliger reported the first documented siting of A. columbianus in Plumas County, California on the western slopes of the Sierra Nevada's (Groves 1992). This is also the highest elevation (1,097 meters) the banana slugs have ever been documented at. A biotic factor that restricts the distribution range of the banana slug has been studied by Mark Denny who attributes their high cost of mucus (slime) locomotion (1980). Two disadvantages of adhesive crawling of gastropods, according to Denny are that the adhesive power of the slime must be overcome by the animal, and that the mucus must be produced to replace the expended slime during movement. These factors limit the distance to which slugs will crawl in search of food or mates. Banana slug slime also serves as defense from predators, helps them retain moisture, reproduce, and may also serve as nutrition if necessary (Harper 1988).
Source: http://online.sfsu.edu/bholzman/courses/Fall00Projects/bananaslug.html

Status

Not evaluated

Behavior

One disitinctive behavior of the Banana Slug is how it gnaws off its penis when disengaging from intercourse. Another interesting behavior that the Banana Slug engages in is estivation. The slug buries itself in forest debris, secretes a protective layer of mucus, and becomes inactive. Estivation occurs during hot, dry periods to prevent the slug from dessication. Banana Slugs also hibernate when the temperature gets very low.
Source: http://animaldiversity.ummz.umich.edu/accounts/Ariolimax_columbianus/

Habitat

Damp forests are the habitat of preference. Rarely found in cosmopolitan areas.
Distribution is North America:
- U.S.: Alaska, California, Idaho, Oregon, Washington
- Canada: British Columbia

Reproduction

The slime of the slug contains pheromones to attract other slugs for mating. These slugs are simultaneous hermaphrodites, and reproduce by exchanging sperm with their mate. They produce up to 75 translucent eggs, which are laid in a log or on leaves. Slugs mate and lay eggs throughout the year. The adults provide no further care for their eggs beyond finding a suitable hiding spot, and the eggs are abandoned as soon as the clutch is laid.

Food

Banana slugs love to eat. They usually feed in the day during spring and fall. Mushrooms are the banana slug's favorite food. But they eat almost anything. They will munch on both living and decaying plants, bulbs, lichen, algae, fungi, animal droppings and animal carcasses. It is thought that their habit of cleaning up the forest floor helps disperse seeds throughout the forest. Not to worry about your garden. If you find a slug there it is probably there by accident. Banana slugs prefer the dense forest to your garden and rarely eat the vegetation growing there. Their diet includes fungi, feces and carrion of other slugs, and detritus and necrotic vegetation, lettuce, lillies, mushrooms and poison oak
Source: http://acdrupal.evergreen.edu/naturalhistory/animalia/mollusca/gastropoda/stylommatophora/arionidae/ariolimax/ariolimax-columbianus

Predators

Raccoons, garter snakes, ducks, geese and salamanders sometimes eat banana slugs; they roll the slugs in soil to bind the slime. Juvenile banana slugs are sometimes eaten by shrews or moles.

Defense

The caudal mucus plug covers the caudal pit which serves as a defense mechanism

Migration

All populations of this species make significant seasonal migrations.

Evolution

The banana slug is a mollusk, which came from the sea. Their stages of evolution can be seen in other various species of land and sea mollusks. Therefore, slugs are believed to have evolved from marine snails and to have once been protected by a large shell (Harper 1988). The tremendous adaptation variation in slug traits such as size and color, make their fossils challenging to classify. Not to mention the challenge of identifying their soft bodies, which become distorted and faded during fossilization (Runham 1970). A “slug” is actually a word describing their type of body. Divergent evolution is evident in the variation between internal and external shells. Studies of slug anatomy have determined that the current slug shape has evolved through parallel evolution both aquatically and over land, deriving from snails (Harper 1988). Pulmonate species of mollusks in the intermediate stages of land evolution maintain shells that are too small to actually protect and contain their bodies effectively (Gordon 1994). Other’s, like the banana slug, conceal remnants of their shell within their small bodies. The caudal mucus plug covers the caudal pit which serves as a defense mechanism, and may also allow banana slugs greater access to nutrients through arboreal means (Richter 1980). Land snails have limited themselves to conditions of high moisture, the need for protection from light and heat, but have moved away from their dependency on calcium rich soils due to the shedding of their external shell. In retrospect, they also lost their prized protective barrier, allowing predators easy access to a terrestrial treat. In return, banana slugs are able to live in a wider range of environments. They have also become quite mobile with their elastic sleek bodies and gained the ability to live below ground for extended periods of time, as deemed necessary as in places like southern Alaska (Harper 1988).
The Cambrian Period of the geological time scale is the first division of the Paleozoic era in which the ancestral wormlike mollusca existed. It was probably during this time span (~500-570 million years ago) that large aquatic invertebrates existed with skeletons and hard shells of chitin or lime. Their shells have preserved their fossils much better than their slug decendents (Funk & Wagnall 2000). During the Devonian period (~ 395 million years ago) invertebrates began to leave the ocean, probably due to increased solar radiation and warmer wet conditions on land. It can only be hypothesized that this is when various snails left the ocean for land, some eventually losing most of their shell and becoming slug-like.
Source: http://online.sfsu.edu/bholzman/courses/Fall00Projects/bananaslug.html

Uses

Banana slugs have been used as food by Yurok Indians of the North Coast and by German immigrants in the 19th and early 20th centuries. A yearly festival and contest is held at Russian River (California) including slug races and a contest for recipes - though, even when fed corn meal to purge them or soaked in vinegar to remove slime, the slugs' flavor is not always well regarded, and the most successful entries are often those in which the flavor is unnoticeable.