The humble snail is undoubtedly one of the most commonly encountered non-fish aquarium residents, and one that can become both a blessing and a curse. While many aquarists enjoy keeping snails, or see benefits of them, many types of snails can rapidly reproduce in the aquarium, seeming to overtake the tank and becoming a pest. Some types of snails seem to defy the laws of the universe, simply appearing in tanks unheralded, from nowhere, and exploding into vast populations.
An invasion of snails in the home aquarium can become a real problem for many aquarists. Snails are living organisms, using up oxygen and releasing carbon dioxide, eating food and excreting waste, living, breeding and dying in the aquarium. They can become a major part of the bioload – a fact many aquarists seem to ignore. Snails are, unfortunately, part of the tank’s stock, and reduce the number of fish the aquarium can support.
As populations of snails explode in the aquarium, it also becomes increasingly likely that some of them will somehow make it out of the tank and into the wild environment. This doesn’t require the aquarist to become desperate to reduce his snail population and release them; simply, it means that the more there are, the greater the odds of them escaping somehow – and we’ll look at snail escape methods shortly. Once in the environment, snails can have a devastating impact.
The diet of snails more or less crosses the board of available foods, and for convenience, they can be divided into four major feeding groups, though few are exclusively within one group. These four groups are the primary scavengers (i.e., those that eat detritus, dead organisms, etc.), the plant-eating snails, the grazing snails, and the carnivorous snails. Grazing snails are the most important and common of these groups, and feed primarily upon what is called “aufwuch.” Aufwuch is a mixture of algae growing on surfaces (periphyton) and various organisms that live within it, ranging from bacteria to even insect larvae.
Snails can be incredibly destructive upon arriving in the wild. Their voracious appetites mean that they can devour huge amounts of food, while reproducing as quickly in the wild as they do in our aquaria. Their hard shells make them difficult for most predators to eat, and those that do eat snails are often specialized. I’ve previously written about the beautiful Snail Kite, a raptor that lives in the Florida Everglades. This beautiful bird makes it living eating the native Florida Apple Snail. Unfortunately, the apple snail most commonly sold in the aquarium and pond trade is not the native snail, but an Asian variety. There’s a very minor difference in the shape of the shell, which prevents the snail kite from getting to the meat of the snail. As the invasive snails have displaced the native snails, populations of Snail Kite have been diminishing. Says Rachel O’Leary of Invertebrates by MsJinkzd (www.msjinkzd.com), “It’s very difficult to tell the species (of Apple snail) apart under dime to nickel sized diameter,” which is the size these snails are commonly sold.
Additionally, as the populations of the invasive apple snail increases, populations of the native snails decrease. The invasive snail can do a tremendous amount of damage to the plants of the Everglades wetlands. Many pond keepers have mistakenly put apple snails in their ponds to control algae, and seen just how much damage these animals can do to emergent plants.
Similarly, snails can act as important vectors for disease organisms. Many types of snails are known to share their shells with leaches, planarians and other nasty customers. The Malaysian Trumpet Snail is known to harbor a type of trematode parasite that has adversely effected wild populations of the endangered Fountain Darter.
Even those pesky bladder snails that show up in the home aquarium can be problematic. As difficult as they are to eradicate in the aquarium, they can be impossible to remove from wild sources. Most snail-toxins are not species specific and quite toxic to other invertebrates, resulting in the deaths of aquatic insects, crustaceans, and native snails. Hand removal is near impossible, leaving the ecosystem to just hopefully adapt to the introduced species. This can result in a wildly changed environment, and not for the better.
Obviously, aquarists can do a lot to help protect wild waters from invasive snails. First and foremost, aquarists should be careful to avoid introducing snails into the wild. Many, many aquarists will purchase snails to control algae in outdoor ponds, including the Asian Apple Snail and the Chinese (or Japanese) Trapdoor Snail. Both of these species can become invasive, and both of them gladly cross land. Apple snails lay a mass of eggs that may hatch as many as 200 offspring, rapidly over populating a pond. Given even a small rainstorm or morning dew, and these animals begin to wander from the pond, across the lawn, and potentially into a storm drain and on to the local river. Birds and other animals also may assist in moving them. Buy only tropical – not winter hardy – snails from a reputable dealer, or – better yet – purchase only native snails. Additionally, consider addressing the cause of the algae, rather than relying on snails to clean it. High fish loads, too much fish food, and not enough pond plants all contribute to algae.
Indoor aquarists should use caution when disposing of snails, or when disposing of material – including water – from tanks with problem snail populations. It’s very easy for snails or snail eggs to “hitch hike” on aquatic plants, gravel, etc. thrown into the garbage. From there, it is very easy for them to find their way into nature. Aquatic plants should never simply be thrown out anyway – they should be dried fully, preferably in an oven at 350 degrees, before disposal. This prevents their introduction as well.
I have transferred the pesky Malaysian Trumpet Snail between tanks on nets, gravel vacuums, and other equipment. This snail is a true survivor: there’s an anecdotal, probably true story that circulates of an aquarist desperate to be rid of them. The aquarist removed all the fish from the aquarium, poured bleach in the tank and then scrubbed it. After washing all the bleach from the tank and gravel, he refilled it and watched in horror as the Malaysian Trumpet Snails emerged from the gravel – a scene out of the Aquarist’s Friday the 13th, indeed.
A snail that can survive a shot of bleach can survive a shot of chlorine, and most species of snails are fairly tolerant of chlorine. What this means is that even if you flush snails down the toilet or drain, they stand a good chance of surviving to make it into our waterways. Additionally, they can grow in phenomenal numbers in drain systems, surviving off the. . . uh, detritus and foul our plumbing.
Asked how to properly dispose of snails, Rachel echoed my advice on never simply throwing them in the trash. Instead, she recommends freezing them or crushing them. Crushed snails make an excellent treat for virtually all fish who will eagerly gobble up the usually inaccessible bit of escargot.
A much more important step to preventing snail introduction to the wild is to prevent their infestation of the aquarium. Next month, we’ll take a look at how to prevent and control snails in the home aquarium. My thanks to Rachel O’Leary of MsJinxzd.com for answering all my snail related questions!