Mystery of the Month: Worms in Aquarium may be Planaria

Small Floating Worms in My Warm Water Aquarium
April 13, 2010
Whats that bug please help…i have been an avid reader for at least 3 years now and have seen your both grown to what it is now…i live in Sierra Madre Ca near you if i recall in some posts…. ok to the point i have small worms in my warm water aquarium 82 – 83 degrees they are about quarter inch in length and do nothing but float around and wiggle…what are they?..and how can i get rid of them? …the tank is about 20 gallons and houses 3 algae eaters 1 peacock eel and 2 red crabs..i have another tank same size same temp. no worms only difference is the sub-straight in the tank w/ worms is sand ..please assist . P.S i have no image due to the size and resources to capture the image .. TY
Long time reader first time caller…Sean
Sierra Madre Ca

Unknown Aquarium Worms

Hi Sean,
Your aquarium is freshwater and we don’t know if it has plants.  We also don’t know where the sand came from or if there are snails present.  We also don’t know how long the tank has been established, when the worms first appeared, or if there have been any recent introductions to the aquarium.  An aquarium is a closed system, and anything in the aquarium is introduced when things (including plants, animals, furnishings or water) are added by the aquarist, and sometimes organisms may be introduced because they are airborne.  Worms are interesting creatures.  They sometimes develop from encysted larvae like the Gordian Worm or Horsehair Worm.  The North Dakota Department of Entomology website has a good explanation of this phenomenon.  Some parasitic worms prey upon snails, and it is possible that your worms were introduced with snails.  We don’t have a conclusive answer for you, but we will continue to research this topic.

We had some additional thoughts.  You may want to collect a sample and try to have it identified.  You can try Nathalie at Pasadena Tropical Fish on Colorado Boulevard.  If that fails, the Natural History Museum in Exposition Park may be able to answer your questions.  Since your email indicates that they are free-swimming, they may also be the larvae of some species of fly.  They may also be Planaria.  See the AquariumFish website for additional information.

1 thought on “Mystery of the Month: Worms in Aquarium may be Planaria”

  1. Call Monrovia Canyon Park at 626-256-8282 and see if I’m in the Nature Center. There is a chance no one will answer or someone else will answer. Everybody knows me as Barbara. $5 entry fee per car. I volunteer there in the weekend afternoons if my health permits, for a couple of hours. I have a Digital Blue microscope and can take a picture of your mystery worms. We can send it in the this site or use the photo as an ID tool.
    I think I’ve seen what you are describing, although I have no idea what it is called.


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