Biological Control of Snails and Rodents in the Garden

decollate snail feeding on brown garden snail, courtesy of University of California

Two weeks ago, I wrote about the European brown garden snail and the damage it does to our plants.  I received some noteworthy emails in response.

“I was born and grew up in Southern California,” Patricia Batatian wrote,  “first in Altadena, then in Monrovia and, lastly, in northwest Pasadena.  That voracious snail was everywhere I ever lived, eating almost every plant I loved, including my geraniums.  Several years ago, after raising my family in San Marino — all the while my gardens and lawn plagued by those beasties — the snails disappeared from my property.  They were still in my mother’s yard in Pasadena, in my daughter’s yard in Altadena, and in my other daughter’s yard in Venice Beach.  Even the woman across the street had them in her yard. But not one in mine. What had happened?
“Months after the snails disappeared,” Batatian continued,  “when we had a good rain for a couple of days, I lifted my garage door.  I looked down and saw what appeared to be small, black coffee grounds along the concrete that was protected by the door.  I scooped up some and discovered they were tiny baby decollate snails, the imported snail that preys on the brown snail!  Someone on my block had introduced decollate snails, and they had populated everyone’s yard around me, but they didn’t cross the street. Of course, I divided the little foundlings into separate baggies and shared them with my mother and two daughters who, after about two years became snailless also!  Soon after another rain, I gathered up more babies as before and gave them to my neighbor across the street and her snails also disappeared.  It’s like magic.
“It’s a different life without the brown snail,” Batatian concluded. “ No more going out in the early morning in my garden shoes to step on snails of all sizes munching on my St. Augustine grass before the sun comes up. No more snooping through my cymbidium orchids hoping to find and destroy the snails before the flower buds form, knowing all the while how hopeless it is because you can kill fifty but there are dozens more where you can’t find them.”
Decollate snails were imported from Mediterranean Europe in the 1970‘s as a biological control remedy for the pesky brown snail, native to the Mediterranean as well.  The decollates were especially useful to California citrus growers in overcoming the plague of snails that had taken hold in their orchards.  Rincon-Vitova, a Ventura company that specializes in growing beneficial carnivorous insects that prey on insect pests, grows decollate snails that are sent through the mail.  You receive the snails in a dormant state and place them in 1/4“ of water to wake them up.  100 decollate snails, which is the number an average sized back yard requires for brown snail control, may be purchased for $19, although the company does have a minimum order of $25, which you can easily fill from a vast array of products, including easily germinated seed mixes of plants that, once mature, attract beneficial insects.  You can order  by calling 800-248-2847 or by visiting the website at
Only those of us in Southern California, south of the Tehachapi Mountains, can order decollate snails, since decollates are a threat to indigenous snails and slugs further north.  The downside to having decollates in any garden is that they do enjoy dining on earthworms, which are beneficial in helping to aerate and enrich soil by means of earthworm castings, a euphemistic term for worm poop.

opossum with offspring, courtesy of

If the idea of snails eating snails does not appeal to you, there is another solution to your snail problem.  Lyn Weiss, writing from Chino, recommends utilization of an urban wildlife critter.

“Just have an opossum visit your yard for a few days,” Weiss advises,  “and you will be without snails. I discovered this a few months ago.  I noticed snail shells on my patio and then I saw the opossum. I now feed him nightly to keep him around. He loves wet dog food and donuts!”
Opossums are the most successful marsupials native to the Western Hemisphere.  They are completely beneficial in the garden, consuming not only snails and slugs but rotting fruit, as well as dead rodents, should you have one lying about, as well.  Although opossums climb trees, they are not really interested in hanging fruit but much prefer the soft and over ripened stuff  that falls to the ground.  Due to their weak paws, they are unable to dig in the garden, so if you see an excavated area, blame it on ground squirrels or raccoons, not opossums.  Opossums are also easily intimidated.  They will hiss at you when approached and will go into their famous coma — yes, that’s where “playing possum” comes from — when afraid, but they do not bite.  At the same time, they should not be touched since they carry parasites such as fleas and a bacterial disease that can be passed along to humans.  Should you encounter an opossum in distress, go to the website at to find a local opossum rescue group in your area.

Barn Owl (Tyto alba) eating a field mouse

Speaking of urban wildlife, I had mentioned in a previous column that inviting barn owls onto your property by putting up a nesting box would solve your gopher problem because of owls’ voracious appetite for gophers and other rodents.  There is one important caveat here, as expressed in the following email from Lisa Owns-Viani.  “Barn owl boxes are a great idea,” she wrote,“but they should not be used in any area where rat poison is being used–within a one-mile radius. Otherwise, they are very likely to be victims of secondary poisoning.”  When I asked Owens-Viani if owls confer other benefits to the garden besides rodent control, she answered that “the awe people experience seeing one of these birds at close range is one of those hard-to-quantify benefits but one that few people forget!”  For more information on the role of owls and their ilk as well as the danger they face from rodenticides, visit the website at

Tip of the Week:  It is not a good idea to plant in wet soil but if you just cannot wait until the ground is dry, you can mitigate soil wetness by adding copious amounts of compost prior to planting.  You do not want to walk around, much less stomp, on wet earth since that will cause undesirable compaction which will make planting in it a problem later on.  Of course, if you build planter boxes and fill them with soft designer topsoil and amendments, you can plant whenever you like, rain or shine.

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