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When we hear the word, snail, some of us go "yuck", others shout out "yay". If ever there was a subject aquatic gardeners seem polarized about it's whether to have or eradicate them.
A sure tie-in with any discussion of ponds and live plants has got to be snails. Though these ubiquitous mollusks are found in all manner of habitats, from hot springs in Iceland to mountains of 14,000 foot plus elevation, they are almost always found in association with aquatic plants. Here we'll deal with the slimy, yet integral part of aquatic gardening which is snails.
Who They Be:
How would you reply to the question: "What does biological classification reveal about the Deity"? One famous answer goes, "An inordinate fondness of the beetles, having created so many of them". An examination of the snails, living and fossil, shows the Creator had a liking for the "stomach-footed" mollusks as well. Snails are literally everywhere, except the air; doing everything life-style wise. They inhabit icy mountains, the hottest, coolest, deepest waters. Familiar forms are free-living, annoying us eating plant material in our gardens, aquatic and terrestrial. A few swim in open seas, others make their living as interstitial organisms, livingbetween sand grains. There are snail species that are deadly predators, fancy filter feeders, even parasites, internal and external on most invertebrate groups.
One of the most fun acronyms from the college zoology years was H.A.M., the hypothetical ancestral mollusk; a theoretical common start for many later forms. Fossils dating back before the Devonian, some 380 million years ago, show that basic snail form has been around a very long time. Probably related to the groups long stable existence is the important fact that snails act as hosts, vectors and space parasites for many other species of organisms. Some of these are critical to human health. Liver flukes and schistosomiasis among other scourges require certain snail species as intermediates. Similarly there are known parasitic and infectious diseases of fishes and plants that are transmitted via snails. Snails can, indeed, be bad news; but there are ways to tip the scales in your favor.
Snails; The Good, The Bad, The Slimy:
Older texts laud the use of snails as scavengers, stating that the exception to their usefulness is the breeding fishes, where snails may devour eggs and young.
Another practical snail use is originating nutrient cycling. To start up new systems Socolof mentions the genus Ampullaria (mystery, apple snails) for culturing infusoria, a microscopic amalgamation used as a first food for egglaying fishes. Snails bring along the starter culture for this critter bouillabaisse wherever they go.
"Canary in a cave?" Snails, especially the air-breathing (versus strictly gill breathing) species, may function as bioassay organisms. When the water fouls they head to the surface.
Most modern works surveyed point to the detractions of snail employment. The 'mystery' of the named snails in the genus Ampullaria used to be their mode of reproduction. I think it's really whether they are alive or not, and possibly about to pollute your system with their stinky disintegration.
Regarding their claims of maintenance, in all honesty snails are not great scavengers. Most all species can and will become opportunistic omnivores; eating plants, other invertebrates, even fishes given the chance. To save my fishy 'sole', neither catfishes nor snails do well exclusively on waste-products; they both should be purposely fed nutritious foodstuffs. Also, an apologia for blue-green algae and diatom (brown) scums. Not much, including snails will eat this stuff. For these it's best to look to root causes; inadequate filtration, too much light, over-fertilization, and correct.
Most snails are hermaphroditic, both male and female; everyone they meet is a hot date. Cross fertilization is the rule, though many small species are known to self-fertilize. A notable single-sex exception is the mystery snail, Ampullaria cuprina (see photo above)..
Oh, and yes, they eat aquatic plants!
If You're Going To Use Them:
Despite the previous mono-atribe, you're still a snail lover? Good for you. The following pertinent notes apply to you and your creepy-crawly friends.
Remember; like catfishes relegated to a janitorial role, snails are not just pooper-scoopers. Learn what your species eats by reading and practice, and expressly provide it.
Clarifying agents, metal-based fish medications and most dye types are toxic to mollusks. You'll want to remove your snails before treatment. By the by, many snails can tolerate moderate salt exposure, to about one teaspoon per gallon. I suggest adding the dose over a period of three days. There are times and places where tap water contains appreciable amounts of copper, iron, other items you want to resist. The usual advice to make frequent partial water changes, as opposed to massive or none, applies here.
Snails need this element for their shells and metabolism. If you have soft (let's say less than 10 German degrees of hardness, or DH), acidic (under 7.0 pH) water, you need supplementation. Thin, pitted shells are generally indicative of calcium deficiency. You can purchase granular calcium carbonate, add a little marble, limestone, dolomitic, coralline rock/gravel, or a little piece of 'food block' for your snails.
I'm not joking. The larger snails can/will leave the system, especially at night. Keep your water level down a bit. If you find your aquatic snails in the garden, plop them back in the water; in all likelihood, your snail(s) will survive.
Good Snails: "The Only Good One Is A _______ One"
If you inserted "Clean" in the blank above, this section's for you. Definitely the most important item on what snails you acquire is their source: CULTURED; that is, from a farm, breeder that has grown them in the absence of other organisms that you want to avoid. For instance the flukes (roundworms) that are the cause of eye-fluke disease in fishes have a complex life-cycle, meaning they pass through one or more intermediate hosts, in this case a bird and a snail, before getting into the fish. By breeding and rearing snails in controlled environments, e.g. ones without birds, 'the cycle is broken'. Voila, no more parasites. The fish farms in Florida, U.S.A. have done an exemplary job of developing large healthy snails for the ornamental aquatics trade; their snails are clean.
Snails that have been raised for several successive generations in captivity are far less likely to harbor pests & parasites. Never introduce wild caught snails to your system. Let's review. How often should you collect and place snails in your tanks/pond? Never. If you even just handle freshwater snails from outdoors, wash your hands thoroughly.
Some of the species commonly offered to the hobby and pertinent notes for those in the know:
Melanoides (Melania) tuberculata, known as the Malaysian burrowing snail, cornucopia snail for it's long, cone-shaped shell. Originates from East Africa to Southeast Asia. Overall color olive to green with violet bands all over the shell. This snail is one of the best from a maintenance point of view. Some plant breeders even endorse them as non-chewers. They come out and scour the system at night, retreating by light of day. Their downside is that they are livebearers that can easily overrun a tank. These 2.5cm (1 in.) beauties are true tropicals and will perish in water below 18C (@64F).
Ampullaria (Pomacea) australis, A. caniculator, A. paludosa are the very large, apple, golfball, snails; the first two hail from South America, the last is a Floridian. These brutes attain 6cm (2 1/2 inches); now that's a snail! They have long breathing tubes to aid respiration by poking out of the water's surface. These giants are ravenous plant eaters. They reproduce by laying their pink to orange eggs in a clump above the water's edge.
Ampullaria (Pomacea) cuprina, the mystery snail of the U.S.. Many color varieties; black, to flavistic yellow to pure albino forms. This is the snail for the aquatic gardener as far as I'm concerned. you can actually control Ampullaria proliferation as the sexes are seperate and they're easily sexed. Males have a convex operculum, the trapdoor that they pull in to cover their soft bodies, and those of the females are concave. For those up-to-the-last-minute know-it-all types, the New World Ampullaria species are now placed in the genus Pomacea.
Planorbis corneus, Marisa rotula, Segmentina victoriae and others are sold as ramshorn snails, immediately identifiable by the shape of their shells. Color ranges gray to a gorgeous deep red. Ramshorns are hermaphroditic and multiply faster than proverbial rabbits.
Viviparus malleatus Japanese livebearing snail. This is a good old-timey outdoor pool and goldfish tank snail. 3cm (1 1/4"). Young born looking like miniature adults. Also great for coldwater systems are the papershell snail, Radix auricularia and the Australian red snail, Bulinus australianus.
Bad Snails That Are Offered In The Trade:
Physa species. To 3/4 inch. These things eat everything and reproduce like weeds. Also to be avoided the burrowing snails in the genus Stagnicola, freshwater limpets of several genera, &...
You Want Plants, But Not Snails? Prevention:
Assuming you've done your best to acquire initially clean and healthy plants, you must examine the same very carefully. With practice snails and their egg masses are easily spotted and scraped away with a fingernail.
Beyond physical inspection and cleaning various molluscicide (snail-killing) baths or dips are recommended. Some of these are sold pre-mixed in the trade. I've found the ones based on aluminum sulfate (alum) and potassium permanganate (KMnO3) to be the most safe and effective.
If this were a perfect world, which, Dear Reader, I know it's not, we'd all have a quarantine system to stabilize, harden and rid new introductions of unwanted co-travelers. Should you inherit for a rich relation or win the lottery, a quarantine phase of a few weeks is recommended.
A mention of another source of snail infiltration, 'live' freshwater foods. If you collect your own, be careful; commercially cultured, prepared foods are not as suspect.
You've Got Them, Now How Do You Get Rid Of Them?
Prevention is, of course, the best course of action to keeping snails out of your ponds, but once you've got them, can you give them the boot? Often, yes, at least to a degree. Methods of eradication fall into the following natural order, from most to least desirable: Biological, Manual, Chemical.
Are the first line of offense in reducing snail populations. Note I didn't say wiping out snails entirely. Don't be disappointed if what you end up with is a predator/prey relationship with fat hunters and scarce, but present snails.
Cichlids for the job include the lowly Convict/Pink Congo to the specialized Africans, Haplochromis placodon, Chilotilapia rhoadesi, Lamprologus tetracanthus among others. As usual with this diverse family, you may be minus the snails, traded for cichlid-destroyed plants, excavation... Be wary of keeping large cichlids and live plants together for long.
Snail-Eating Turtles: I mention in an effort to be thorough. In the old pet-fish store days we used to 'lease/lend' such turtles to aquarists who wanted to rid their systems of snails. They worked.
Lots of Fishes will bug snails (possibly to death); Bettas and their relatives, the Gouramis; swordtails & guppies...
Waterfowl: Here they are again! For temporary snail eradication duty; maybe their filthiness is tolerable.
Manual Means: Feeding Trays, Forceps...
And I do mean manual, as in by hand. It may seem tedious; that's because it is! But removing snails by hand can be instructive, as a lesson in religious tolerance or video game practice.
Hey, looking to increase your 'catch per unit effort' (a fisheries term)? Lay out some freezer burned, or boiled vegetable material or sinking pellet food in a glass dish in the middle of the system at nightfall. In the morning you'll find gazillions of snails concentrated in the area where they can be easily removed.
Chemical Control: An Oxymoron For Sure
The least desirable means of snail eradication, being too toxic, dangerous. If you're going to resort to poisoning, thin the herd first by the methods described under physical removal; baiting and hand-netting.
If you consider semi un-selective poisoning to be the modern way to rid your system of snails, do purchase a product specifically formulated for this purpose and utilize exactly per instructions. In particularly, be accurate as to how many real gallons of water are in the system. There are about 7.5 gallons per cubic foot of water, but a better approximation can be had by "timing" the filling of a known volume (e.g. five gallon "pickle" bucket) and timing the time it takes to fill the system.
Those pretty blue copper compounds labeled as snail-i-cides are the most efficacious; be wary of nicotine and organophosphate treatments. If still not dissuaded, please see Sections E ii) b and c) re chemical use and safety.
I'll just mention in passing the various schema I've run across utilizing direct and even alternating current (yep, that's electricity) for zapping snails. Don't do this. I'd skip trying mollusk electrocution with or without fishes in the system. In fact, if you're using economic poisons, you'd do well to remove the fishes during the 'treatment', if at all possible.
Are snails necessary for an aquatic garden? No. Are they desirable? In some cases, some species, maybe. They can add interest, varying algal control, and a capacity for nutrient cycling; but snails do have their downsides. Many types are uncontrollably prolific; they are known disease carriers for fishes, humans, plants, you name it.
If you don't want snails you will want to:
1) Carefully screen, dip, possible quarantine all new plant introductions.
2) Utilize bio-controls like some of those listed here,
3) Dedicate yourself to routine manual search, removal/destruction of slimy types,
4) Or least desirably, wage a semi-selective chemical poison war, hopefully negatively impacting what you want to eliminate while not harming what you hold dear.
Most growers of aquatic plants will tell you that snails can quickly multiply and destroy a system if not kept in check. My advice to earnest aquatic gardeners is to avoid them.
Hey you snail lovers; as sung by Bella AbSlug, "Happy Snails to You, Until Me Meet Again..."
Anon. 1975. The Snail- Aquarium Aid of Pest? Aquarium Digest Intl., 2(1):75.
Barnes, Robert, 1987. Invertebrate Zoology, 5th Ed. Saunders.
Forsyth, Doug. 1988. A Practical Use For Snails!! The Nekton 8/88.
Masters, Charles O. 1981. Livebearing Snails. TFH 11/81.
Masters, Charles O. 1984. The Great Pond Snails. TFH 7/84.
Pointier, Gloria & Jean Pierre. Ampullarid snails: forgotten creatures of the freshwater world. TFH 7/95.
Socolof, Ross B. 1980. Snail Update & a New Pale Snail. FAMA 10/80.
Starmuhlner, Ferdinand. 1989. The Alluring Apple Snails. TFH 1/89.
Werner, Ewe. Snails in the Aquarium. TFH 9/83.