Snail farmers must be aware of several predators, parasites and diseases if mortality rates are to be kept to a minimum. Snails have many natural predators, including members of all major vertebrate groups, carnivorous snails, ground beetles, leeches and even predatory caterpillars.
Humans also pose great dangers to snails in the wild. Pollution and destruction of habitats have caused the extinction of some snail species in recent years. Human poachers pose a great danger to farm grown snails as well!
The major predators a snail farmer may have to deal with are field mice, rats and shrews, frogs and toads, thrushes, crows and domesticated birds such as ducks and turkeys, lizards and snakes, drilid and carabid beetles, and millipedes and centipedes. The frogs tend to take only the young snails, while the reptiles eat both eggs and snails of all ages.
In areas with high bird predation, it is necessary to place cover nets over the pens. Keeping some of the other predators out may require building fences around the pens. The fences should be between 15 and 30 cm high and dug well into the ground *It is also advisable to set bait or traps outside the snail farm area.
Leftover food should be removed daily from pens because some predators, particularly rats and field mice, are attracted by the uneaten food. These predators can decimate a farm in a few days.
In Ghanaian studies, the major parasite on snails was found to be a fly, Alluaudihella flavicornis. This species belongs to the same family as the housefly and the adult resembles the adult housefly.
A. flavicornis lays 20-40 eggs in the snail shell or on the snail. The eggs hatch in about one week and the small, cream-coloured worms start feeding on or in the body tissue. They feed until the body is reduced to a putrefying mass, and then pupate within the shell.
After a 10-day incubation period, the adults emerge. The best protection against these flies is to cover the pens with nylon mesh.
Meanwhile, the entire life cycle of Alluaudihella flavicornis, a parasite of Achatina achatina, takes 25-40 days. However, the main predators are humans looking for a nutritious meal at the snail farmer’s expense. Snail farmers must introduce any legal measures they consider necessary to protect the farm against poachers.
Ectoparasitic mites are sometimes found on the snails in hutch boxes. They seem to be secondary parasites, usually occurring on inactive snails.
Some nematodes are known to attack European species of edible snails. However, there are no known reports of nematodes parasitizing A. achatina.
Little is known of the diseases which attack A. achatina in West Africa. As snail farming increases in popularity, more research will probably focus on this area. The main disease that has been reported to date is a fungal disease, spread through physical contact by the snails licking slime from each other’s bodies.
The two major diseases affecting European species may also affect African species, because the organisms that cause these diseases do occur in the natural range of A. achatina. The first is a bacterial disease, caused by Pseudomonas; it leads to intestinal infections that may spread rapidly amongst dense snail populations.
The second disease is caused by the fungus Fusarium, which parasitizes the eggs of Helix aspersa. The affected eggs turn reddish-brown and development stops.
This disease is commonly referred to as ‘rosy eggs disease’.
Basic hygiene prevents the spread of diseases. Pens should be cleaned out regularly to remove excreta and uneaten food, as well as any other decaying matter that may serve as substrate for pathogenic organisms.
It is also advisable to sterilize the soil in hutch boxes by steaming or heating every time they are being prepared for a new batch of egg clutches (i.e. when the breeders are transferred to the boxes for egg laying).