crawls across the tidal mudflats
- Size
- Shell: 1–2 cm
- Lifespan
- 2–5 years
- Diet
- Herbivorous and detritivorous: feeds on algae, bacteria and decaying organic matter on mudflat surfaces. Can breathe air and survive out of water for long periods. Tolerates wide range of salinities.
- Habitat
- Estuaries, mudflats and salt marshes throughout New Zealand. Live on surface of the mud, crawling slowly across the flats as the tide goes in and out.
- Range
- Throughout North and South Islands, Stewart Island and Chatham Islands in estuaries, mudflats and salt marshes. Most common in sheltered harbours and estuaries with muddy substrates.
- Endemism
- Endemic
- Main Threats
- Habitat loss from coastal development, estuary reclamation and pollution from urban and agricultural runoff. Sedimentation from land clearance. Climate change affecting estuarine conditions.
- Population
- Not Threatened. Common in estuaries throughout New Zealand. Ability to breathe air and survive out of water for long periods allows them to live in high intertidal zone where few other snails can survive.
- Conservation Status
- Not Threatened
- Human Risk
- harmless
- Handling Note
- intertidal snail, safe to handle
- Conservation Note
- Endemic mollusc; widespread in intertidal mudflats and not subject to conservation assessment.
- Te Ao Māori
- The Pūpū-papa is the Māori name for the mud snail, recognising its place as a resident of the estuary flats. They were not a traditional food source, being too small and too muddy to be worth the effort. Today, they are the snail of the mudflat, overlooked by everyone except the birds and the children who pick them up and watch them crawl across their hands.
The small, grey, unassuming snail of the estuary floor. A snail that breathes air.
The mud snail has a small, conical shell, usually about 2 centimetres long, with a dull, grey-brown to olive colour. The shell is thick and strong, with deep spiral grooves. The body of the snail is a dark, grey-black, with a distinctive flat foot that it uses to crawl across the mud. A snail that is easy to overlook.
These animals are the air-breathing survivors of the mudflat. Unlike most marine snails, mud snails have a lung, not gills. They can breathe air directly, which allows them to survive out of water for days. They crawl across the mud at low tide, grazing on the algae, bacteria and organic matter that grows on the surface.
When the tide comes in, they climb up the stems of saltmarsh plants or seal themselves into their shells to wait for the water to go out again. They are hermaphrodites, possessing both male and female reproductive organs. Mating occurs during low tide, and eggs are laid in gelatinous masses on the mud surface.
The eggs hatch into tiny, free-swimming larvae that drift with the currents before settling onto a suitable mudflat. Mud snails are the snails of the estuary, the ones seen crawling across the mud when digging for cockles or pipi. They are too small to eat and too common to notice.
But they are a vital part of the estuary ecosystem. The estuary is muddy. The mud snail crawls across the mud at low tide, flat foot, conical shell, breathing air. The tide comes in. The snail climbs a saltmarsh stem and seals itself shut. It does not know it is vital. It does not know it is easy to overlook.
It just wants to eat algae. The engine of the mudflat. The mud snail keeps the estuary clean, one mouthful of mud at a time. The pūpū-papa is the Māori name. The snail does not know that either.