Rats are highly adaptable omnivores that have successfully colonized nearly every human environment. As resourceful scavengers, rats consume a wide variety of food sources, from seeds and grains to meat and household waste. This raises a natural question regarding their consumption of common garden invertebrates, specifically slugs, and what drives this dietary choice. Understanding this interaction requires examining the rodents’ general feeding patterns and the potential biological consequences of consuming such prey.
Dietary Habits of Rats
The two most common species, the Norway rat (Rattus norvegicus) and the roof rat (Rattus rattus), are known for their opportunistic and generalized feeding strategies. Norway rats, often called brown or sewer rats, are broadly omnivorous and readily consume meat, fish, seeds, grains, and various invertebrates. Their diet is often a reflection of the resources most readily available in their environment.
Roof rats, also known as black rats, tend to be slightly more herbivorous, favoring fruits, seeds, and grains. Despite these preferences, all rats require a consistent source of protein and fat to support their high metabolism and rapid reproduction. Their scavenging behavior means they will sample virtually any potential food item to determine its caloric value and safety.
The Specific Interaction: Rats and Slugs
Rats are known to consume slugs and snails, though these mollusks are generally not a preferred or staple food source. Evidence of this consumption often comes from gardens or natural areas where rats leave behind piles of empty snail shells after extracting the soft body. This behavior confirms that rats will actively prey on these invertebrates when they encounter them.
The primary deterrent that makes slugs a less appealing meal is their thick layer of mucus, which serves as a protective defense mechanism. This highly viscous, sticky secretion is energetically costly for a rat to process and may be chemically unpalatable. Consumption of slugs becomes significantly more common when a rat’s preferred diet, such as human food waste or stored grains, is scarce, forcing the rodent to rely on accessible protein sources.
Parasite Transmission Risk
A significant consequence of a rat consuming a slug is the transmission of the rat lungworm, Angiostrongylus cantonensis. This parasitic nematode has a complex life cycle that requires both a definitive host and an intermediate host. Rats act as the definitive host, where the adult worms reproduce in their pulmonary arteries and lungs.
The infected rat excretes first-stage larvae (L1) in its feces, which slugs and snails then ingest. Once inside the mollusk, the larvae develop into the infective third-stage larvae (L3). The cycle closes when a rat consumes an infected slug, allowing the L3 larvae to mature into adult worms in the rat’s body. Accidental ingestion of infected slugs or their slime can also infect humans and domestic animals, such as dogs, who become accidental hosts.
Habitat Overlap and Food Availability
The likelihood of a rat resorting to eating slugs is directly tied to the availability of other food sources in its immediate habitat. In dense urban and suburban areas, rats benefit from a stable, high-quality, and high-protein diet derived from human food subsidies like garbage and processed waste. This consistent access to easy calories means urban rats rarely need to engage in the effort of hunting and consuming mollusks.
In contrast, rats living in rural, agricultural, or less densely populated natural settings experience more variable and less reliable food sources. These rural populations must adopt broader foraging strategies and often compete with native omnivores and herbivores for resources. This environmental pressure increases the probability that a rat will resort to consuming invertebrates, including slugs, to meet its nutritional requirements.