Surveying for slugs on your property is simple, but it helps to know where to look.
Here is a video of Dr. Lorrin Pang with the Department of Health surveying for slugs:
There are essentially two ways you can get a thorough understanding of the snails and slugs on your property: 1) Creating a trap to collect them and then checking it during the daytime or 2) Going out at night to survey. Each method is detailed below. Choose whatever will work best for your situation and resources. If you are a night owl, go survey your yard with a flashlight. If you are an early bird, set a trap and check it during the day. Regardless, consider watering a few hours before you survey, particularly if it has not rained in a while. Slugs in particular hide deep underground during dry periods and watering will encourage them to come out to feed.
PRECAUTIONS: Do not handle slugs or snails with your bare hands, use disposable plastic gloves and tongs or chopsticks dedicated for that purpose. Consider controlling slugs during your survey. Options include placing them in a saline solution of 7 parts water to 1 part salt for 48 hours to kill the parasite. Or you can bag and freeze them until solid.
Trap method: The various methods below depend on a slugs, and snails, need to seek shelter during the daytime. Basically, by offering them shelter, you can find out what is living in your yard and garden.
- Board trap: Use a board with risers to elevate it approximately 1 inch off the ground. Slugs and snails will hide underneath, check during the daytime. See: http://ucanr.edu/sites/CalSnailsandSlugs/Management/Traps/
- Plastic bag trap: cut open a large plastic garbage bag to make a sheet of plastic. Then fold it in half over and over, sprinkling water in it each time. Place it in a shady cool area and weight it with a rock. Adding dog or cat food to the trap will help attract semi-slugs.
- Plastic pot trap (suitable for plant nurseries in particular): Place small 2-4 inch plastic pots upside down with an attractant such as a wet lettuce leaf inside. Scatter them around potting benches or garden beds
Check the trap and record the slugs and snails seen. Pictures of the top, head and tail are very helpful!
Real-time survey method:
- Water beforehand. If you are going out in the evening, water in the late afternoon or choose a warm rainy evening, this will encourage slugs and snails to come out and feed and will give you a better understanding of the slugs and snails around your home and garden.
- With a flashlight go out for a minimum of 15 minutes looking for slugs and snails. Focus your efforts on the following areas:
- Heavily vegetated areas, especially gardens and fields where plants have been damaged by feeding
- Spaces beneath rocks, asphalt, or cement pieces that are in loose contact with the ground surface
- Spaces beneath discarded wooden boards and planks, fallen trees, logs, branches and other debris
- Damp leaf litter (not wet or soggy), compost piles, and rubbish heaps
- Under flower pots, planters, rubber mats, tires and other items in contact with the soil
- Vegetation, fences, and other raised materials
- Standing rock walls, cement pilings, and broken concrete
- Again, wear gloves and avoid handling slugs and snails directly.
More about real-time surveys can be found here: https://www.aphis.usda.gov/import_export/plants/manuals/emergency/downloads/nprg-tropicaltg.pdf