aka California blackworm (Lumbriculus variegatus)

Kingdom: Animalia
Phylum: Annelida
Class: Oligochaeta
Order: Lumbriculida
Family: Lumbriculidae
Genus: Lumbriculus
Species: Lumbriculus variegatus 1
Lumbriculus is characterized by possession of two bifid setae in each of its four segmental bundles. Members of this genus often have no reproductive organs and reproduce asexually by fragmentation. Sexually mature individuals are rarely found in nature. Living specimens have dark green pigment on the anterior body wall. This pigment is responsible for the common name ''blackworm''. This species feeds, in part, on algae. It typically lives in shallow water along the shores of lakes, ponds and marshes. It usually has its anterior end embedded in sediment while its posterior extends to the water’s surface to lie flat in the air-water interface. This behavior permits it to take advantage of the food in organic rich and oxygen poor sediments by taking advantage of the high oxygen tensions at the interface…. Full-grown worms have 150-200 segments. 2

Blackworms are small fresh-water worms that look much like slender earthworms that are only about an inch long. They are popular lab animals as they are easy to care for and propagate. They are somewhat common in the classroom (although not nearly as frequent as the common earthworm Lumbricus terrestris), and are also useful in such things as chemical toxicity testing. They are also used as live food for assorted fresh-water hobby fish and animals. They are not the same as bloodworms which are sometimes called redworms (a common name they confusingly share with tubifex worms). Bloodworms are actually the aquatic larvae of the midge fly, are often sold frozen or dehydrated, and can cause terrible allergic reactions in people with dust mite allergies.

Like earthworms, blackworms are segmented, have a double row of tiny bristles that help them move, and are hermaphrodites. They burrow through substrate looking for food, leaving their breathing end sticking out unless threatened. Startled, they will pull their tails in and disappear completely. Occasionally they will take to swimming instead of crawling, and whip like a giant flagellum through the water. When they do this, they somehow manage to keep their head end steady (at least I think it’s their head end!), while the rest of the body flails, making a perfect wave pattern. Looking closely at them, one half often looks darker than the other, and their segments are clearly visible almost like a banding. They are pink, again like earthworms, because their blood also contains hemoglobin for oxygen transport (no, not the same kind of hemoglobin as ours).

Unlike earthworms, blackworms are more slender on their ends, tapering more gradually. They also can regenerate two new worms if you cut one in half. The regenerated portions are lighter in color than the dark portion of the original worm. They tend to come apart fairly easily and, as the excerpt above states, they don’t often reach sexual maturity in the big bad world. Also unlike an earthworm, they also don’t have a clitellum, the pale swollen band that generates the cocoon in which an earthworm deposits its egg.

My familiarity with blackworms comes from using them as a live food treat for my fish. They are popular among aquarium enthusiasts as an effective food for finicky fish. Many who breed their fish swear by blackworms as an infallible spawn trigger (when all other conditions are appropriate). Blackworms are generally available live from pet stores that are serious about their fish, and frozen from pet stores that don’t want to work that hard for a buck but are willing to keep a freezer stocked. They also make an excellent food for amphibians, such as salamanders.

Blackworms are high caloric food for your pet fish (I don’t know enough about newts to say). It’s generally a bad idea to feed your fish as many blackworms as they can eat more than once a week. I’ve seen larger fish gobble them up by the clump until their bellies are distended. It’s rather like one of us eating a 36 ounce Black Angus steak in 10 minutes. It’s not something to do everyday. And a balanced diet requires a few other things making it into your fish once in a while!

Blackworms are considered more desirable than tubifex worms by some in the hobby. Tubifex worms eat bacteria and most used to be harvested from sewage effluent runoff. Needless to say, the water these things sit in takes a while to clean, and while perhaps not bad for the fish, do you really want to come in contact with it yourself? Some think that bloated fish result from infections caused by the bacteria load in tubifex worms. Some think that both blackworms and tubifex worms are extremely rich food and overfeeding causes an ammonia spike in the tank that can lead to fish deaths. Some think that a fish, over-eager to nosh on a tasty worm, can choke on one.3 I dunno folks. I do know that everything from my smallest tetra to my largest flag acara loves blackworms, and none have ever choked to death. I’ve a heavily planted tank, so no ammonia spikes either! My cichlids have also spawned after being fed blackworms, which seems to substantiate the breeders.

Meanwhile, tubifex creep me out a little as they are softer worms than blackworms, bright red, and they gather in clumps and whip around so quickly they look like they’re vibrating. I much prefer the slower, more predictable movement of blackworms.

Blackworms come home
Luckily, blackworms are extremely easy to store, if you aren’t squeamish. If you are squeamish, what’re you doing buying live food in the first place? Take that nice handful you just bought and find a clean, straight sided plastic container with a tight fitting lid. The container should be able to hold several cups of water. Now, when you get your blackworms home, place them in that container and wash them under a stream of de-chlorinated water. Let the stream swirl them around. Disturbed, they’ll start clinging to each other and fairly quickly form a tight clump. At this point, you can pour off most of the water and any dead worm pieces floating around. Note that they smell a little like blood, and be amazed at the ubiquity of hemoglobin.
Fill the tub with about an inch of water, so that the surface of the water is just level with the clump of blackworms. When the worms relax, the clump will unknot and settle under the water. Make sure there are no ‘volunteers’ in the batch. I once found flukes in a batch of blackworms, which may or may not have led to a fluke problem I had in one tank.
Try not to handle the worms or their water directly, and wash your hands well. Some folks have allergic reactions to contact with blackworms. I’ve never had a problem, but it’s a good practice anyway.
Blackworms stay for dinner
Now that your blackworms are washed, you can feed some to your fish. If the blackworms are in a clump (you can encourage this by swirling the container) you can pick bunches up on the end of a non-slippery stick, like the blunt end of a clean bamboo skewer. If there aren’t that many, and they aren’t too clumped up, I use a pipette to suck up a bunch at a time to squirt into the tank. The pipette I use has the tip cut off to make a 1/4 inch in diameter opening. This helps prevent damage to the worms, and clogging.
Blackworms chill out
Once you’re done feeding the fish, cover the container of blackworms and stick it in your refrigerator. Make sure the container is clearly labeled, or someone (even perhaps you), may get an unpleasant surprise during a late night snack raid. Rinse the worms with cold water once every other day or so, and you are all set. You won’t need to feed them, as they can go weeks without food, especially when kept cold.
Blackworms start a family
So, you want to keep a live culture of blackworms? It’s absurdly easy. Keep in mind that harvesting them can be somewhat problematic depending upon your substrate. I have cultures of blackworms in most of my tanks. The fish in those tanks snack on them at will, and I don’t give them new ones. I only buy blackworms for the tanks where I can’t keep a culture going because the fish are too good at catching them.
There are two ways to go about this if you want to keep a culture separate from your fish. You can have a stagnant culture or a non-stagnant culture.
The stagnant culture. Get a basin with a lid (not airtight). Fill it with about 2 inches of clean water that has no chlorine in it. Rip up some paper towels and lay the strips into the water. Add some blackworms. Feed a small amount of sinking fish food every day, but be careful not to overload the food and make the water toxic. Don’t feed them more if there’s still food visible. Now, wait for them to do their wormy thing and make more blackworms. Use a pipette or a dropper to harvest them. Top off the water whenever it drops noticeably.
The non-stagnant culture. Adding aeration improves yields, and all you need do is stick an air stone into the stagnant culture. I’m lazy, so I simply added a culture of blackworms to my clean tank. I’ve taken a 2.5 gallon fish tank that doesn’t have any fish, and stuck in a small amount of gravel, a box filter with nothing much but filter floss, some plants and some snails. Things go in there for quarantine before I stick ‘em in my tank and perhaps give my fish a communicable disease like ick. Right now, I’m culturing snails and blackworms, so I dump in a bunch of fish food about once a week. The snails mean I never have food rotting in the tank, and if I forget to feed them, they can eat algae and plant matter. The blackworms can go weeks without food, but without food, they don’t multiply. When I want some blackworms, I suck ‘em up with that handy dandy pipette.
Now, say I want to catch blackworms in a tank with a real substrate layer, one that will kick up clouds if I dig around it in futilely trying to catch blackworms. Well, I throw in a pinch of aquarium salt, up to a teaspoon, all in one spot. As the grains dissolve, the blackworms rush out of the substrate trying to escape. It is much easier to suck them up in a dropper this way. If you do this, just remember that you’ve added salt to the tank. A small amount can be beneficial to your fish, but small amounts can build up over time, and blackworm habitats are not marine!

riverrun says: Interestingly, when I kept a marine aquarium in the ''old'' days, I fed everything, including anemones, blackworms. I had very good luck w that 100 gallon box. Sub-sand filter only--I never put a mechanical filter on the thing in over eight years. Red worms creeped me out, but I bought them too, reluctantly.

Thanks riverrun! I've never had a marine tank, but this makes sense to me. Just like I've fed live adult brine shrimp to my fresh-water tanks, I can image marine tank occupants eating fresh-water live food with glee. Just don't expect the blackworms to survive if uneaten. On the other hand, if you don't feed massive quantities all at once, this won't be a problem.

And see? It's not just me, about the relative creepiness of redworms!

More comments!

momomom says I confirm the ''bring on the babies'' property of live food. I've bred angelfish, gouramies, and krinbinsis with little more than a partial water change and some live food. I used to keep a daphnia culture, hatched brine shirmp and yeah, had blackwoms in the tank that I hadn't put there any time recently. Also snails, my fish viewed snails as another sourse of live food. Of course the latest passion has been the gliders, who love mealworms so I've done a mealworm culture as well.

Sources:

1 The Norwegian Environmental Education Network, Systematic tree of organisms: Lumbriculus variegatus:
www.miljolare.no/data/ut/art/?lang=eng&or_id=125
2 Fox, Richard. An Introduction to the Study of Freshwater Oligochaetes: Laboratory Exercises for ES 300, Biodiversity, 2000.: www.lander.edu/rsfox/300oligoLab.html
3The Krib: www.thekrib.com/Food/bloodworms.html

Want to get a clean culture of your own? Not cheap, but clean and healthy: www.carolina.com

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