Snail farmers must be aware ofseveral predators, parasites and diseases if mortality rates are to be kept toa minimum. Snails have many natural predators, including members of all majorvertebrate groups, carnivorous snails, ground beetles, leeches and evenpredatory caterpillars.
Humans also pose great dangersto snails in the wild. Pollution and destruction of habitats have caused theextinction of some snail species in recent years. Human poachers pose a greatdanger to farm grown snails as well!
The major predators a snailfarmer 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 andsnakes, drilid and carabid beetles, and millipedes and centipedes. The frogstend to take only the young snails, while the reptiles eat both eggs and snailsof all ages.
In areas with high birdpredation, it is necessary to place cover nets over the pens. Keeping some ofthe other predators out may require building fences around the pens. The fencesshould be between 15 and 30 cm high and dug well into the ground *It is alsoadvisable to set bait or traps outside the snail farm area.
Leftover food should beremoved daily from pens because some predators, particularly rats and fieldmice, are attracted by the uneaten food. These predators can decimate a farm ina few days.
In Ghanaian studies, the majorparasite on snails was found to be a fly, Alluaudihella flavicornis. Thisspecies belongs to the same family as the housefly and the adult resembles theadult housefly.
A. flavicornis lays 20-40 eggsin the snail shell or on the snail. The eggs hatch in about one week and thesmall, cream-coloured worms start feeding on or in the body tissue. They feeduntil the body is reduced to a putrefying mass, and then pupate within theshell.
After a 10-day incubationperiod, the adults emerge. The best protection against these flies is to coverthe pens with nylon mesh.
Meanwhile, the entire lifecycle of Alluaudihella flavicornis, a parasite of Achatina achatina, takes25-40 days. However, the main predators are humans looking for a nutritiousmeal at the snail farmer’s expense. Snail farmers must introduce any legal measuresthey consider necessary to protect the farm against poachers.
Ectoparasitic mites aresometimes found on the snails in hutch boxes. They seem to be secondaryparasites, usually occurring on inactive snails.
Some nematodes are known toattack European species of edible snails. However, there are no known reportsof nematodes parasitizing A. achatina.
Little is known of thediseases which attack A. achatina in West Africa. As snail farming increases inpopularity, more research will probably focus on this area. The main diseasethat has been reported to date is a fungal disease, spread through physicalcontact by the snails licking slime from each other’s bodies.
The two major diseasesaffecting European species may also affect African species, because theorganisms that cause these diseases do occur in the natural range of A.achatina. The first is a bacterial disease, caused by Pseudomonas; it leads tointestinal infections that may spread rapidly amongst dense snail populations.
The second disease is causedby the fungus Fusarium, which parasitizes the eggs of Helix aspersa. Theaffected eggs turn reddish-brown and development stops.
This disease is commonlyreferred to as ‘rosy eggs disease’.
Basic hygiene prevents thespread of diseases. Pens should be cleaned out regularly to remove excreta anduneaten food, as well as any other decaying matter that may serve as substratefor pathogenic organisms.
It is also advisable tosterilize the soil in hutch boxes by steaming or heating every time they arebeing prepared for a new batch of egg clutches (i.e. when the breeders aretransferred to the boxes for egg laying).