Lizards are a diverse group of reptiles whose diets range dramatically from strict herbivores to dedicated carnivores. Many lizards are opportunistic feeders, classifying as insectivores or omnivores, consuming a wide array of insects and other small invertebrates. For species that forage on the ground, the slug represents a viable source of nutrition.
Slugs as a Staple in the Lizard Diet
Slugs often become attractive prey due to their high nutritional density. Their soft body is rich in protein and moisture, providing a crucial water source for lizards, particularly those living in arid or seasonally dry habitats. This high-moisture content is important for survival, especially for juveniles with smaller fat reserves and a higher need for hydration.
Lizards that incorporate slugs into their diet typically employ an active foraging strategy, slowly pursuing their prey on the ground. Because slugs are slow-moving, they present an easily accessible meal for many terrestrial lizards. Unlike snails, the lack of a hard shell makes slugs simple to consume without the need for specialized jaw strength.
Species Variation in Slug Consumption
The likelihood of a lizard consuming a slug depends heavily on its species, size, and ecological niche. Ground-dwelling lizards, such as skinks, are among the most enthusiastic slug predators. Blue-tongued Skinks, for example, actively seek out and consume slugs and snails as a regular part of their diet.
Other terrestrial lizards, like the European Slow Worm (a legless lizard), also readily feed on slugs and earthworms. This preference is tied to their burrowing habits, placing them in direct contact with subterranean prey. In contrast, arboreal species, such as most geckos, rarely encounter slugs in their elevated habitat, focusing instead on flying insects, nectar, or fruit.
Larger lizard species, including many monitors, are less likely to consume slugs as an important food item. The small caloric return from a slug does not justify the effort for a large reptile. Therefore, slug consumption is concentrated in small to medium-sized, ground-dwelling, and actively foraging lizard families.
Biological Barriers to Eating Slugs
Despite the nutritional value, slugs present several biological challenges. The most immediate defense is the thick, sticky mucus or slime slugs secrete when threatened. This slime is difficult to remove and can make the slug unpalatable, challenging the lizard’s ability to swallow and digest the meal.
A greater threat is the potential for parasitic infection, specifically the rat lungworm (Angiostrongylus cantonensis). Slugs and snails act as intermediate hosts for this nematode, and a lizard consuming an infected slug can ingest the parasite larvae. This can lead to serious health issues, including neurological damage or death.
Slugs can also accumulate toxins from the plants they consume, which are then passed up the food chain to the lizard. If a slug has fed on a poisonous fungus or plant, the lizard risks ingesting harmful secondary compounds. These combined risks mean that many lizards will only eat slugs opportunistically or when safer prey is unavailable.