Last Updated: 2/21/17
Flatworms - including planaria
This page is about various freshwater worms associated with freshwater aquaria and ponds as well as terrestrial worms.
I also have a page on saltwater feather duster worms and discuss various marine worms (peanut worms, bristleworms, etc.) on my marine pages.
Here is a link on aquatic worms:
Blackworms are sold to feed small animals. They work great to feed hatchling turtles, fish, newly morphed amphibians, and other small animals. I mean to create a page on my site one day on how to take care of the blackworms. I add water to mine and put them in the refrigerator. Each day after I remove some to feed my African dwarf frogs, I pour off a little water and add new water. Blackworms will survive/live in aquariums and ponds indefinitely. I have added them to my ponds in the past as well where they continued to live.
Aquatic Foods - sell live blackworms
Simply Discus - sell freeze dried blackworms.
There are a number of species of earthworms or Oligochaeta. Tubifex are an inch long, are red, and live in tubes in bottom mud. Chaetogasters eat small animals with their large mouths and grow to half an inch. Deros build tubes in debris, grow to about half an inch, and have bristles. Aeolosomas grow to half an inch, live in debris or on plants, and can have colorful spots. All species tend to stay on the bottom or in debris, dirt, etc.
Flatworms or Platyhelminthes include flukes, tapeworms, and turbellarians. The first two are familiar parasites. The latter move around on surfaces using cilia and eat small living or dead animals. Planaria, a common turbellarian, often over-reproduce in aquaria but I do not think they are a problem in ponds. Other turbellarians are also rather harmless. Dugesias tigrina is the largest free-living flatworm, growing to an inch long.
If small white creatures are seen crawling all over the glass and ornaments, especially at night, they may be planaria. Planaria commonly show up in tanks with an excess of food. Most are introduced to an aquarium from other aquaria with live foods like black worms, live plants, or anything else moved from an active aquarium that has them. There is some belief that they can survive in freeze-dried or frozen foods. If a lot of food is left in a tank; including dead and dying fish, snails, other animals, and plants; then a few planaria may divide into hundreds very quickly. They usually reproduce by asexual fission. Their heads are shaped like arrow heads. If a tank is found to be infested, planaria can be controlled by a good vacuuming of the gravel and better tank maintenance. To remove more planaria, see the next section on controlling planaria. Planaria will eat dead fish, fish eggs, and immobile fish larvae (fry newly hatched). They do not pose any risk to mobile fry or adult fish.
Controlling planaria in freshwater aquaria:
1. Set out bait like meat in a mesh bag. Remove the bait a few hours after the lights go out on
the tank. It should be covered with planaria. Throw away and repeat until the population goes
2. Add planaria eating fish to the tank. One species is the paradise fish.
3. Vacuum the gravel very well and do a 50% water change. Often, planaria proliferate when the tank is too dirty. This will remove not only some planaria but their food source as well.
4. Reduce the foods added to the tank. Planaria often proliferate if too much excess food is provided.
5. As a last resource, tear down the tank. See here for information on tearing down tanks.
Horsehair worms (Gordius), or Gordian worms, grow to a whopping 40 inches long. They look like horsehair. Even more remarkable, females can lay egg strands 8 feet long. The larvae are parasites on crustaceans, worms, and mollusks. The adults are parasites of crickets and grasshoppers. Their life cycle is amazing. The adults lay eggs in ponds which must be eaten by aquatic insects that then metamorphasize and must be eaten by a cricket where the worm feeds. Then, the cricket must die and fall into a pond for the long adults to being their short life as a free-living mouth-less adult worm.
Here are some links:
Parasites of the extinct Rocky Mountain grasshopper - the site seems to be gone
Gordian (horsehair) worms
On 11/15/08, Peggy sent this photo of a large whitish worm around 10-12 inches in her pond
with salamanders. We were not able to identify it. Horsehair worms are the only ones I know
that get that big but all the ones I read about are dark in color and very skinny. Do you know
what it is?
On 5/21/10, Betsy in North Carolina sent these photos of a worm for identification. It may be a
Pond worm and backswimmers
Leeches prefer shallow, slow moving, warm water with lots of detritus. Some are scavengers, some hunt small animals, and others suck blood. Sizes range from a few inches to almost two feet! Some species of leeches, or Hirudinea, include helobdellas, erpobdellas, macrobdellas, and haemopsis. Colors and sizes range but all are flat and segmented. If your pond develops an overabundance of fish or people-sucking leeches, you can place a piece of raw beef or other bloody meat in the pond on a string or in a mesh bag. Remove later, and it should now be covered in leeches.
Most leeches found in water gardens are scavengers and not blood suckers. If they are on the fish, that is when treatment should be done to kill them. If they are not on the fish, they are probably doing no harm. Keeping the pond cleaner will reduce their numbers.
My ponds are absolutely FULL of leeches now (now being 2009?). I believe they got in with some blackworms that I added to the pond. I have never seen the leeches attach to the fish or me so they most likely are just scavengers. Whenever I pull out something from inside the pond, there are leeches on it about 1/4 inches long. They stick to whatever I am working on. Even the hose at full blast cannot remove them sometimes (yes, I have to touch them!).
Leeches may also show up in aquariums (most often included with blackworms) but are most often harmless scavengers. There is no need to eradicate them if they are not harming the fish. If they are to be removed, it is better to do it with bait than chemicals which can harm other animals and plants in the tank.
Leech - one of the leeches from the 50 gallon pond stuck in the bucket on 3/6/12 when I cleaned that pond.
For some interesting information on the biology of some leeches, visit the site on Australian parasitic leeches.
I took these photos of my PondMaster filter from the 153 gallon pond on 8/8/10. The filter is
covered in things every summer. For years, I thought these were limpets. Why? Someone told
me that they were, and when I looked at certain limpet photos, they looked identical. Then, in
October of 2012, I happened to see a photo of ribbon leech cocoons (egg cases). Moreso than
the limpet photos, these looked like what I had. I never saw any leeches in or coming out of the
cocoons but they did seem to go flat after a certain period of time. They were also only obvious
in the warm months and not in the cold ones. I am pretty sure that these are, in fact, leech
cocoons on my filter.
Leech found while cleaning the 153 gallon pond on 3/30/16, head to the left.
Mealworms are, in fact, not worms at all! They are beetle larvae. My page on them is here.
Nematodes, or Nemas, are roundworms. They live in the bottom of ponds and are common. Nematodes constantly thrash in an S shape. Some are parasites of crustaceans or larger worms; others eat animals and some eat plants. They only grow to 0.1 inches. One of the 1000 species in freshwater is Chronogaster gracilis.
Proboscis worms, or Nemerteans, are also called ribbon worms. They have a skinny, flat body less than an inch long. Their proboscis is an extension two to three times the length of their body which they can retract into their body. They move around eating small creatures. The only North American species is Prostoma rubrum.
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