PROTOCOLS FOR COLLECTING TERRESTRIAL SNAILS AND SLUGS
FOR MALACOLOGICAL STUDY
Terrestrial snails and slugs are generally nocturnal creatures that avoid sunlight and adverse conditions such as extreme heat and cold, and low humidity. They are most active at night, on dark, cloudy days, and also after a rainfall, when they emerge to feed and/or search for mates. When light levels increase (such as in the early morning), or when conditions become increasingly dry, they will take refuge under an object where it is shaded and where there remains some humidity.
In order to successfully collect snails and/or slugs, the mollusks’ preferred conditions need to be kept in mind. Collecting on a warm summer night after a light to moderate rainfall will be the most productive time, when these mollusks are active and out in the open. At any other time, therefore, one must look for suitable microclimates where they will have taken refuge:
- under rocks and boulders that are lying on the ground surface, where there are spaces between the rock and the ground for humidity to collect and space enough for the mollusk to hide. If the boulder is partly buried, the snails or slugs may be hidden around its edges,
- under boards and planks, as well as under fallen trees, logs and branches,
- under flower pots and planters,
- in damp leaf litter (not wet or soggy), where it is cooler and moist enough to attract a mollusk, but not so wet as to drown it,
- in greenhouses, where optimum conditions for warm temperate and tropical plants are also ideal for snails and slugs,
- in garden centers, where there is a concentration of many different food plants, as well as the possibility of introduced mollusks from other regions of the country,
- in fields and gardens where plants have been damaged by feeding snails and slugs: look at the base of plants, under leaves, or in the “hearts” of compact plants, such as lettuce or cabbage.
Follow slime trails: terrestrial mollusks leave behind them a characteristic glistening trail of mucus that can be used to track them down.
Keep in mind that urban and suburban backyards and gardens may be just as productive in terms of numbers of mollusk species as well as numbers of individuals as unspoiled wilderness areas. A general rule of thumb, though: synanthropic species (those associated with human activity such as agriculture and human habitation) are more likely to “travelling species,” those that have been introduced from other parts of the world and are often horticultural or agricultural pests. Usually, native species tend to remain where there is a minimum of human disturbance.
Snails and slugs should be preserved in a manner that is consistent with how they will be studied. For identification requiring dissection, the snail or slug has to be drowned in water before being placed in 75% ethanol: the specimen first should be placed in a vial or specimen bottle of water that is then sealed as it is held under water to make sure that no air bubble remains inside. The container should be placed in a cool place for about 12-24 hours, by which time the mollusk will have died in a fully extended (relaxed) condition. The specimen then should be transferred to 75% ethanol, and then submitted for identification. However, if DNA analysis is to be used to identify a specimen, such as for the North American Slug Project, it should be killed in 75% ethanol and submitted as soon as possible for identification.