The Biology of Snails

• Snails belong to the class of mollusks known as Gastropoda. They have a single coiled shell and are "stomach-footed," meaning they have a muscular foot under their body that enables them to move. The teeth of the snail are rasp-like, and are set in a flexible radula (tongue) that can be extruded and retracted as needed. There are two main groups of pond snails--pulmonates, which breathe air using lungs, and operculates, which use gills to take oxygen from water.
  
  

Benefits of Snails

• Freshwater snails can lay eggs that provide food for fish in the pond, and clear away unwanted organic plant matter, particularly surface algae. Snails also eat decaying matter on the pond's bottom, such as dead animals, leftover foods, and small pieces of plants that have broken off.
  
  

Types of Snails

• The olive nerite is a popular pond snail. This snail will not eat the plants in the pond, preferring algae. Their eggs hatch only in slightly salty or brackish water, so overpopulation is not an issue, and their eggs provide food for fish. Other good choices of snails for ponds include Japanese trap door snails, which tend to leave aquatic plants alone, and ramshorn snails, which are known to be avid consumers of algae.
  
  

Snails and Reproduction

• Pulmonate snails are hermaphrodites, with each individual snail being able to both fertilize and be fertilized. They are very fast reproducers due to this trait. Operculates have separate male and females, and breed at a slower rate. An example of an operculate is the apple snail. Ramshorns are pulmonate, and multiply very rapidly. Olive nerites are also pulmonate, but as stated earlier, their eggs require brackish water to hatch.
  
  

Possible Cons

• There are possible drawbacks to having snails in garden ponds. Some species may eat aquatic plants that are intended to be decorative. Others may eat fish eggs or newborn fish. If the snails multiply to a great degree, they can overcrowd the pond. Overpopulation may result in a die off, when there is not enough food for the snails, and the snail corpses may pollute the pond.