Various taxonomic families of land slugs form part of several quite different evolutionary lineages, which also include snails.

The shell-less condition has arisen many times independently as an example of convergent evolution, and thus the category "slug" is polyphyletic.

In drier conditions, they hide in damp places such as under tree bark, fallen logs, rocks and manmade structures, such as planters, to help retain body moisture.

[11] Some species of slug, such as Limax maximus, secrete slime cords to suspend a pair during copulation.

[15] Slugs play an important role in the ecosystem by eating decaying plant material and fungi.

Most species of slugs are generalists, feeding on a broad spectrum of organic materials, including leaves from living plants, lichens, mushrooms, and even carrion.

[16][18] Slugs can feed on a wide variety of vegetables and herbs,[19] including flowers such as petunias, chrysanthemums, daisies, lobelia, lilies, dahlias, narcissus, gentians, primroses, tuberous begonias, hollyhocks, marigolds, and fruits such as strawberries.

It is the case in the Philomycidae (e. g. Philomycus carolinianus and Phylomicus flexuolaris) and Ariolimacidae (Ariolimax californianus), which respectively feed on slime molds (myxomycetes) and mushrooms (basidiomycetes).

[17] Species of mushroom producing fungi used as food source by slugs include milk-caps (Lactarius spp.

Because some species of slugs are considered agricultural pests, research investments have been made to discover and investigate potential predators in order to establish biological control strategies.

With many examples among reptiles, birds, mammals, amphibians and fish, vertebrates can occasionally feed on, or be specialised predators of, slugs.

[23] One of its congeners, the Northwestern garter snake (Thamnophis ordinoides), is not a specialized predator of slugs but occasionally feeds on them.

[33][34] The slug mite, Riccardoella limacum, is known to parasitise several dozen species of molluscs, including many slugs, such as Deroceras reticulatum, Arianta arbustorum, Arion ater, Arion hortensis, Limax maximus, Tandonia budapestensis, Milax gagates, and Tandonia sowerbyi.

The nematode worms Agfa flexilis and Angiostoma limacis respectively live in the salivary glands and rectum of Limax maximus.

Flies in the family Phoridae, specially those in the genus Megaselia, are parasitoids of Agriolimacidae, including many species of Deroceras.

In contrast to the general behavioral pattern, the Kerry slug retracts its head, lets go of the substrate, rolls up completely, and stays contracted in a ball-like shape.

This aggressiveness is also influenced by seasonality, because the availability of resources such as shelter and food may be compromised due to climatic conditions.

[42] Excessive buildup of slugs within some wastewater treatment plants with inadequate screening have been found to cause process issues resulting in increased energy and chemical use.

[43] In a few rare cases, humans have developed Angiostrongylus cantonensis-induced meningitis from eating raw slugs.

Parasitic nematodes (Phasmarhabditis hermaphrodita) are a commercially available biological control method that are effective against a wide range of common slug species.

These include beer traps [de],[47][48] diatomaceous earth,[49] crushed eggshells, coffee grounds, and copper.

[50] Salt kills slugs by causing water to leave the body owing to osmosis[51] but this is not used for agricultural control as high soil salinity is detrimental to crops.

Hammond et al. 1999 find maize/corn and soybean in the US to be more severely affected under low till because this increases organic matter, thus providing food and shelter.