ShadyGardens Blog

September 12, 2010

Planarian: Eater of Earthworms and Enemy of the Garden

Filed under: earthworms, flat, orange oil, planarian, slugs, snails, worm — shadygardens @ 1:38 pm
When rearranging containers at the greenhouse recently, I ran across something unusually icky–a planarian. 
Land Planarian
Planaria are non-parasitic flatworms existing in most parts of the world. Some live in ponds, while others are terrestrial and can be found under flower pots or in other moist places. You’ve probably seen a planarian before, but might have mistaken it for a slimier than usual earthworm. 
A land planarian is long, flat, and either gray or brown with several black stripes running the length of the body. A planarian can be extremely long. I have seem them almost a foot in length. And, once again, this creature is not native to Georgia, but is thought to be originally from China. 
Planarians have been found in the United States since about 1901. Planarians just love greenhouses, because they provide everything a planarian needs to survive: moisture, humidity, and something to eat. Planarians appear to be dispersed with plants–we might unknowingly bring one home  in a plant we purchased. 
Planarians have a mouth that also serves as an anus. How gross is that?! 
Where might you find a planarian? They like places that are dark and moist, so look beneath container plants, boards, or rocks. If you’re lucky enough to experience a heavy rain, they might even be seen on the soil surface, especially under shrubs. If you have a worm bed, look for a planarian attached to an earthworm.
High humidity is vital to the survival of a planarian, and they are seen most often in spring and fall. 
Planarians move about by gliding on a stream of mucus, and if they find themselves up on the leaves of a plant, they can lower themselves using a stream of that mucus. Yuk! They leave a shiny slime trail like that of a snail. You might be thinking, yes, this is grossly interesting, but what does all this have to do with gardening?
Planarians are cannibals and will eat each other. They will also eat slugs, which could be a help to the gardener. Perhaps this is the grossest fact yet–a planarian can even use some of its own tissue for food if necessary.
But what concerns me is that planarians eat earthworms! The earthworm is a gardener’s good friend, and I want to protect all my earthworms. A planarian infestation is devastating to a worm bed and reportedly is capable of destroying the earthworm population of an entire farm. 
I won’t describe how the planarian turns the earthworm into food, because that’s even more yucky than what I’ve written so far. 
You should not try to destroy this pest by mashing it, since it will regrow from small parts of itself. So if you chop up a planarian, you’ll be multiplying it. In the past I’ve just tossed them into the garbage can, but experts recommend melting them with a spray of orange oil.

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