The granite slug is a land-dwelling mollusc, which can reach lengths in excess of 1.5 metres and weigh over 25 kilograms. At rest, a granite slug is approximately 30 centimetres wide, with a roughly semicircular cross-section. The dome-shaped upper half of the slug is mostly featureless, except for the eyestalks on the head. These stalks contain a highly-developed eye with acuity far beyond any known mollusc, and comparable to that of some humanoids.
Granite slugs are also noted for their slime, which they deposit on any surface they come into contact with. This slime acts as a moisture retainer for the slug and as a passive defense, being highly corrosive to most organic and some inorganic matter, although once removed from the slug's skin, the powerful acids and oxidizers in the slime rapidly neutralize. This neutralization occurs by yet-unknown means and generally within five minutes under normal conditions. In extreme cold, the effect of the slime is weakened but may last many hours. Due to this, slug trails in subzero environments may present a hazard to humanoids and should be avoided.
Today, the granite slug is most commonly found on Coruscant, having been introduced to its surface by the planetary government some three centuries ago. The original home of the slugs is now lost to history, as they were introduced to hundreds or even thousands of other planets by an unknown race. Little is known regarding this ancient society, although evidence suggests extensive activity some fifteen millennia prior to the foundation of the First Republic.
The granite slug is named for its unique nesting habit. Weeks or months before mating, a slug locates a flat rock known as a nest base, and spends up to twenty three hours a day circling a small area. As the slug travels back and forth over the nest site, its slime dissolves the surface of the rock, creating a depression. While the slugs are known to nest in a variety of rocks and minerals, they prefer nesting in granite when possible. Slugs seeking a nest base exhibit impressive memory, sometimes returning to rock faces they had only visited once months or, in one exceptional case, years earlier.
Prior to the introduction of the slugs to Coruscant, the abandoned surface of the planet was littered with refuse and ruins, some of it many millennia old. The slugs are capable of consuming and breaking down almost any material thanks to their incredibly abrasive mouth and corrosive slime. Tests indicate that most inorganic materials are not digested by the slug, but simply broken down and later excreted in the slime or as solid waste.
A favourite food of the slugs appears to be the compressed blocks of organic waste produced by the citizens of Galactic City. Another common food is stresscrete, which is present in mass quantities at the surface, and is believed to be sought out by the slugs as a source of essential minerals.
Due to the conditions in Coruscant's undercity, granite slugs are not generally active at specific times, but rather at any time when moisture is present. This may occur either when the nightly surface rain drains below the main city platforms, or when the undercity's microclimate produces rain. From the undercity's many massive refuse piles, a slime trail may be found and followed to either a solitary slug, or if the hunter is fortunate, a slug nest which may house two, sometimes three, adult slugs and a cache of eggs, which are approximately 80 millimetres in diameter and are blue-grey in colour. A nest may hold up to 250 eggs, usually found in clusters of approximately 25.
A community of dedicated slug-chasers exists among the rich of Coruscant, and they organize regular incursions to the undercity in search of granite slugs. The rate at which a slug-chaser successfully locates his quarry is referred to as his "slugging percentage". More accomplished slug-chasers often add this statistic to the rate at which they find occupied nests to calculate their "On-base plus slugging". Outsiders to the slug-chasing community often describe its enthusiasts as obsessive or fanatical, while the slug-chasers themselves insist that their hobby is "the Coruscanti pastime"