Rats are highly adaptable omnivores that thrive in diverse environments by consuming virtually any available food source. This includes various molluscs like terrestrial snails and slugs, which provide a readily available source of protein.
Rats as Opportunistic Mollusc Eaters
Consuming snails is generally not the main diet for common species like the Norway rat (Rattus norvegicus) or the black rat (Rattus rattus), but it becomes a frequent opportunistic choice. This predation is most often observed in environments where snail populations are dense, such as cultivated gardens, damp woodlands, or near drainage systems. When other food sources become scarce, snails and slugs offer a consistent, slow-moving meal.
The presence of rats preying on snails is often confirmed by finding distinctive piles of empty shells, known as “middens,” typically located in sheltered areas. Rats often transport the snails to a secure, hidden spot, such as under a bush or rock, before consuming them. These middens serve as clear evidence of the rat’s presence and their specific dietary activity in the area.
Specialized Shell-Breaking Techniques
To access the soft body of a snail, rats utilize their powerful, continuously growing incisor teeth to breach the shell’s calcium carbonate defense. The exact technique employed often depends on the size and structure of the shell. For larger, coiled shells, the Norway rat creates a characteristic break from the outer edge of the last whorl inward, moving toward the columellar muscle attachment site to extract the flesh.
In controlled feeding trials, rat predation damage is categorized into several types, including damage to the aperture (the shell opening), dorsal damage (a breach on the top or side of the shell), and the complete crushing of the shell. The incisor marks left are diagnostic, characterized by ragged edges and impressions typically about 2 mm wide. This precision allows the rat to bypass the snail’s defense and reach the soft tissue inside.
Nutritional Appeal and Associated Health Hazards
Snails provide rats with an excellent nutritional profile. Snail meat is particularly rich in protein (some species contain over 40% protein content by dry matter) and supplies a high concentration of minerals. Calcium is especially important for pregnant or lactating female rats needing to replenish bone density and produce milk.
This nutritional benefit, however, comes with a biological hazard: parasitic infection. Snails and slugs act as intermediate hosts for the rat lungworm, Angiostrongylus cantonensis, a parasitic nematode. Adult worms live in the pulmonary arteries of rats, and the rats excrete the parasite’s larvae in their feces. Snails become infected when they ingest these larvae, which mature into the infectious third-stage larvae within the mollusc’s tissues. When a rat consumes an infected snail, the life cycle is completed, leading to reinfection.