Red slug (Arion rufus) If you have a flower garden, and you live in Europe you will almost definitely recognize this slug, mainly probably because of how much of a pest they are... They can measure up to 6 inches in length! They are usually orange, red, or brown. You should keep them away from flower gardens, as they can completely take over and eat all the plants in a blink of an eye. They're main predators are birds. If you want to handle them, or carry them away from somewhere, keep this in mind: You should never handle mollusks including slugs with dry hands, as it sucks the moisture out of the slugs which will cause death, as they need to keep moist permanently.
Leopard slug (Limax maximus) This another huge species of terrestrial slugs, as it measure up to 7.8 inches in length! It is native to Europe and Asia, but has been distributed to North America and New Zealand. It has multiple stripes and spots which is said to resemble a leopard. You can find them in residential areas, like backyards, flower gardens, greenhouses and under rock and logs near buildings. It also a huge pest in gardens and eat up lots of plants really quickly, especially when they are in large groups. They are similar to Greenhouse slugs, but aren't actually related to them.
Greenhouse slug (Milax gagates) This is a slug smaller than some other slugs in this section, as it can get up to 2 inches in length. They are native to Morroco, Tunisia, and southwest Europe, but have been introduced to many places in the world including the United States. It prefers a habitat near water.