Laver spire shell (Hydrobia ulvae)

Adult laver spire shell group on saltmarsh

Top facts

  • A small snail species, the laver spire shell is between four and six millimetres long.
  • The laver spire shell is often found in huge numbers, sometimes up to 300,000 per square metre.
  • The laver spire shell uses a raft of mucus to float upside down on the surface of the water.
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Laver spire shell fact file

Laver spire shell description

GenusHydrobia (1)

The laver spire snail (Hydrobia ulvae), also known as the mudsnail, has a small, spiralling shell, which is brown to yellow in colour. The snail is grey with spots of pigment (1), and the tentacles are pale with a dark patch towards the tips (2).

Also known as
Shell height: up to 6 mm (2), usually 4 mm (1)

Laver spire shell biology

This snail is often found in extremely high densities; up to 300,000 individuals have been recorded per square metre (1). When covered by the tide, it floats upside down on the surface of the water on a 'raft' of mucus (2). When the tide has gone out, this snail often climbs up vertical objects in order to browse (1). It feeds on silt, fungi, and diatoms, which it scrapes from the sediment surface with the radula, a narrow structure in molluscs that bears teeth and is used to rasp food (2). When floating, the snail also feeds on particles that become trapped in the mucus raft (2).

Breeding occurs in spring and autumn (1); the sexes are separate, and fertilisation occurs internally (2). Egg masses of 4-8 eggs are usually cemented onto the shells of other laver spire snails and become covered with a protective layer of sand grains (2). There is some dispute as to the biology of the larval stage; research has shown that the larvae are planktonic, whereas other researchers have found that there is no planktonic stage, and that the larvae live on the substrate (1).


Laver spire shell range

Widely distributed around all of the coasts of Britain. It is also found in north-west Europe (2).

You can view distribution information for this species at the National Biodiversity Network Atlas.

Laver spire shell habitat

This species is found on mudflats, muddy sand, in estuaries (2) and in saltmarshes (1); it is most common on the middle and upper parts of the shore (2), although it has been found at depths of 100 metres (1). It is often associated with sea-grass beds (1).


Laver spire shell status

Common and widespread.


Laver spire shell threats

Not currently threatened.


Laver spire shell conservation

One of the major habitats supporting this species, mudflats, is a priority habitat under the UK Biodiversity Action Plan (UKBAP). It therefore has a conservation Action Plan. Many mudflats are protected by UK and European legislation, and have been designated as protected areas including Sites of Special Scientific Interest (SSSIs), Special Protection Areas (SPAs) and Special Areas of Conservation (SACs). Mudflats and sandflats are listed as an Annex 1 habitat under the EC Habitats Directive (3).

There may be further information about this species available via the National Biodiversity Network Atlas.

Find out more

For more on this species see the Marine Life Information Network (MarLIN) species account, available at:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:



Of the stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Aquatic organisms that drift with water movements; may be either phytoplankton (plants), or zooplankton (animals).
In some molluscs, a narrow structure that bears teeth and is used to rasp at food.


  1. Jackson, A., 2000. Hydrobia ulvae. Laver spire shell. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. (November, 2002)
  2. Fish, J.D. and Fish, S. (1996) A student's guide to the seashore. Second Edition. Cambridge University Press, Cambridge.
  3. Action Plan for mudflats. UK Biodiversity Action Plan (November, 2002)

Image credit

Adult laver spire shell group on saltmarsh  
Adult laver spire shell group on saltmarsh

© Steve Trewhella /

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