New Zealand screw shell

Body contents

New Zealand screw shell (Maoricolpus roseus) can densely blanket the sea floor with live and dead shells, and faecal pellets. It is a suspension feeder, so can compete with scallops, commercially-farmed shellfish and native species.

What to look for


  • brown, fading to purple or white with age
  • conical shape that is broad to tapered
  • smooth
  • up to 18 whorls
  • around 6cm long, but can be 9cm.
New Zealand screw shell
New Zealand screw shell

Where to look

Look in or around:

  • crevices
  • mud
  • rocks
  • sand.

Likely habitats include:

  • burrowed in to mud and sand
  • shores and shallow waters, up to 130m deep.

Established pest along the east coast of Tasmania, in Bass Strait and from Wilson’s Promontory, Victoria to Botany Bay, New South Wales.

Similar native species

These native species look similar to New Zealand screw shell. They do not need to be reported.

Native screwshell (Gazameda gunnii)

Do not collect samples. This species is threatened.

New Zealand screw shell


  • off-white to light brown
  • narrow tapered shell with marked ridges
  • up to 5cm long (usually approximately 3cm long).


  • up to approximately 140m deep.

Known locations are Cape Moreton, Queensland, southwards to northern and eastern Tasmania, and westwards to South Australian and Western Australia.

Mud whelk (Velacumantus australis)

New Zealand screw shell


  • dirty grey
  • ridged
  • up to 4.5cm long.


  • mangroves
  • mud and sand in shallow sheltered areas, usually among seagrass
  • tidal flats.

Known locations are south Queensland, New South Wales, Victoria, Tasmania, South Australia, and Western Australia.

Terebra lima

New Zealand screw shell


  • flaring lip
  • up to 9cm long.


  • mud and sand
  • 35m to 350m deep.

Know locations are New South Wales, as far south as Trail Bay.



Report it

See something unusual? Report it. Even if you’re not sure.

If you see something you think is a pest:

  • note the exact location (screenshot your map app or enable photo geotagging on your phone)
  • take a photo (use something for size reference, like a coin or note)
  • contact your state or territory authority.


Stop the spread of marine pests

Start with these simple steps:

  • Inspect and clean your boat or yacht. Make sure you check hard to reach areas.
  • Treat the hull of your boat or yacht regularly.
  • Clean and dry your fishing and diving gear after every use.

How you can stop the spread of marine pests.

Your location

Check our marine pests map.

The map shows known pests and pests to look for around Australia.

New Zealand screw shell

New Zealand screw shell (Maoricolpus roseus)

In Australia

Features: Shell brown, fading to purple or white with age. Conical shape, smooth, up to 18 whorls.
Habitat: Shores up to 130m deep.
Affects: Native species, commercially-farmed shellfish.
Movement: Vessels, fisheries and aquaculture.