Every gardener knows that slugs and snails are active in warm weather and absent in cold weather. They come out after it rains or when plants are watered. This makes it the best time to put out your slug and snail pellet baits. They hibernate or die during heat and drought. Snails and slugs are more active on cloudy days and less active on sunny days. But what are the conditions when we know for sure snails and slugs will be active, or won’t?
Slugs and snails travel on slime. The moister their environment, the less slime they have to secrete. For this reason, both slugs and snails prefer to be out after rainstorms, after plants are watered, and at night when humidity is higher.
Nearly all species of slugs and snails prefer relative humidity of 65% or higher. When humidity is falling, the air is drying out, they will initially be more active, but that is because they will be seeking shelter. Desert-dry days with humidity below 20% results in death or estivation (summer hibernation) for most kinds of snails and slugs.
What are the implications of these facts for snail and slug control? If you deprive slugs, in particular, and snails of moisture, they die. If you limit the number of moist hiding places, you limit your snail and slug problems. Cut back brush and leafy vegetation. Remove rocks and fallen wood. Elevate flower pots off the ground and put copper tape around them, this acts as a repellent. Place storage sheds on blocks rather than directly on the ground.
Water In the morning, not in the evening, and water the soil, not your plants. Watering plants in the morning gives the ground time to dry out before slugs and snails begin their nighttime feeding.
Drowning slugs and snails also limits their numbers, but not as quickly as you might think. They have to be completely immersed in water for several days. Adding detergent to dissolve their protective slime helps, as does putting a handful of salt in the bucket of water in which you keep them. You simply won’t be able to drown slugs and snails by watering foliage – but you could drown your plants.
Temperature is also a factor. The most common garden snail, the brown garden snail, can survive temperatures as low as -6.4 degrees C (20.4 degrees F), if they have time to “supercool” first. In the fall, garden snails respond to shortening daylight and lowering temperatures by reducing the amount of water in their bodies and burrowing underground. The lower water content of their bodies enables them to be chilled several degrees below freezing without the formation of ice crystals that would destroy their tissues.
Field slugs can survive temperatures as low as -4.7 degrees C (23.5 degrees F) if they have burrowed into moist soil. The optimal temperature for activity for this slug is 17 degrees C (62 degrees F), and the maximum tolerated temperature is about 30 degrees C (86 degrees F).
You can use the aversion of slugs and snails to heat and cold to trap them for easy disposal. In hot weather, dampen the ground in a corner of your garden and cover it with plywood or a flower pot turned upside down. Slugs and snails will gather in the damp, cooler haven you provide them so you can more easily kill or remove them from your property.
You can also kill slugs and snails with cold. Let them find a winter home under a pile of leaves or a piece of plywood, and then remove their cover the first night you have a heavy frost. The cold will take care of your infestation with no need of toxic chemicals or tedious picking by hand.
Slugs are eaten by certain kinds of beetles, and the scent of those beetles will send them into hiding. If you don’t go out of your way to kill the beetles in your garden, you will probably have fewer snails and slugs on your property. The scent of predators sends slugs and snails away at their top speed – which may be as much as 14 meters (44 feet) an hour!
But the biggest factor in the activity of slugs and snails is one that is most often overlooked. Slugs and snails love the slime of other snails and slugs. Most of the time, a slime trail marks the quickest path to a quick lunch. Slime accumulates where slugs and snails find their food.
Slugs and snails use their slime as a kind of “Google Earth”. They can find their way back to hiding places by traveling down the slime trail that contains their own scent.
And slime can deter predators. Slugs that feed on manure secrete an especially unpleasant smelling slime. So do snails that feed on garlic. Birds, rats, mice, shrews, voles, and people trying to pick up slugs sometimes drop them because of their slimy coating.
Sometimes, however, slug and snail slime is a pathway to love. They release pheromones into their slime to let other slugs and snails know they are ready to mate. Some slugs and snails make a spectacular display of courtship when they find the secretor of the sex scent-laden slime. And the result is 20 to 200 babies.
If you don’t’ want your garden to become a love den, you need to remove slime when you see it. This kind of slime has an unusual consistency. It is a solid when it is simply spread out over a flat surface, but it becomes a liquid when pressure is applied to it. You’ll need to do a little scrubbing to get rid of the slim. Simply hosing it down won’t work.
You don’t need any special products to remove slug or snail slime. A laboratory study at the University of Hawaii found that ordinary tap water was just as effective for removing slime and slug and snail parasites as vinegar or bleach. But each and every leaf has to be washed under and over to be absolutely sure you get rid of both snails or slugs and their parasites.
However, there is one time that you shouldn’t be overly fastidious about removing slime trails from your garden. That’s when you put out parasitic nematodes for natural slug and snail control.
It isn’t just slugs and snails that are attracted to their own slime. Their parasites use it as a homing signal, too. Tiny worm-like nematodes creep along through the soil until they detect the scent of their potential prey. Nematodes are especially attracted to the slime of the common garden slug, Deroceras reticulatum. They intentionally place themselves in slime trails so they will be ingested by any slug or snail that is susceptible to them.