Lumbriculus variegatus, also known as the Blackworm, California blackworm, or the Mudworm, is a natural food for many aquatic animals (such as freshwater fish, crabs, crayfish, axolotl, frogs, etc.). These little worms are so tasty that even picky eaters will not refuse to eat them.
Blackworms are small, non-parasitic worms that can be easily cultured in a home aquarium with very little effort. So, if you already have a fish tank (or keep any other aquatic animals), you can definitely keep and culture blackworms as well.
In this article, I will dive deep into the profile of Lumbriculus variegatus species. You will know more about the life cycle of the Blackworms, how to culture, feed, harvest, and store them for the purpose of feeding aquarium fauna.
What are Blackworms?
Blackworm is a common freshwater oligochaete of the genus Lumbriculus. Although this genus includes 16 species, the most common and available blackworm species for culturing include as aquarium fish food only Lumbriculus variegatus.
Habitat and Distribution of Blackworms
Bcakworms are generally spread throughout North America and Europe. However, nowadays, these worms have been also introduced into Africa, Australia, and New Zealand.
Blackworms inhabit both the sediment and water compartment simultaneously. This species is generally found in the leaf litter along the shallow habitats at the edges of ponds, lakes, marshes, or slow-flowing rivers.
In nature, blackworms are important members of freshwater aquatic communities where they serve in such diverse roles as aiding in the decomposition of organic materials in the sediment and serving as food for animals at higher trophic levels.
How to Identify Blackworms
According to the study, the identification of species is less obvious, due to the lack of reliable non-sexual characters of most nominal taxa.
Size. Blackworms have elongated segmented cylindrical bodies, on average, varying in size between 0.4 to 2.5 inches (1 – 6 cm) in length and up to 1.5 mm in diameter. An adult blackworm has from 150 to 250 segments.
Note: It was also recorded that some blackworms reached an impressive 6.7 inches (17 cm).
Diet: They mostly feed on green algae, detritus, decaying vegetation, microorganisms, and sediment.
Color: in reality, Blackworms are not black but dark green or dark red due to the presence of Hemoglobin (Hb) in their body fluid. This pigment gives them a red color. These worms have a closed circulatory system.
Behavior of Blackworms
It is a slow-moving worm. Blackworms dwell with the head first in the sediment and keep the tail extended in the water, where respiration and photoreception occur.
The positioning of the tail into the water column makes the blackworm vulnerable to predation. Therefore, to protect themselves these worms have developed rapid withdrawal behaviors (escape response) that are triggered by tactile stimulation or even shadow.
Blackworms do not like lighting, they hide from bright light or shadow.
Blackworms exhibit several easily identifiable sublethal responses such as:
- color changes,
- swelling and
In open spaces underwater, tail stimulation evokes helical swimming, while head stimulation evokes body reversal.
Difference between Tubifex worms and Blackworms
There is a lot of confusion on this subject. In some cases, Tubifex worms are sometimes mistakenly sold under the name Blackworms. Thus, many hobbyists believe that Tubifex worms and Blackworms are the same. This is not true.
Although both these worms have been used as feeders, nonetheless, Blackworms and Tubifex worms are different species.
In the wild, Tubifex tubifex often inhabits highly polluted water and may have parasites and other nasty things in them. Even though Blackworms are pretty hardy invertebrates, they are still more sensitive than Tubifex tubifex and prefer a clean environment.
In addition to pollution tolerance, Tubifex worms are able to deal with anoxic conditions for long periods (up to 25 days) by switching to anaerobic metabolism. It was recorded that blackworms can survive only for 12 hours without oxygen by switching to anaerobic metabolism.
up to 300 eggs per worm in 100 days
|Color||Light red||Dark red|
|Movements||Coiling, waving tail||Escape reflex, relatively steady tail|
|Size||20-60 mm||40-60 mm|
|Wet weight (mg)||3-8||0.1-20|
|Life cycle||20-62 days||Unlimited
(If you cut it in half, the two parts will grow into two new ones)
|Densities of specimens (per m2)||very high (up to 400 000)||never exceed 12 000
which corresponds to around 0.1 kg wet weight per m2
Life Cycle of Blackworms
Blackworms are basically immortal creatures. They have the remarkable ability to regenerate time and time again – effectively living forever.
This species reproduces almost exclusively by fragmentation (architomy) and subsequent regeneration.
Interesting fact: Lumbriculus variegatus can reconstruct its entire body from only three original segments. Due to their high regenerative capability, blackworms are used as models for experimental studies of regeneration.
Reproduction of Lumbriculus variegatus occurs by simple year-round division (architomy). Under optimal conditions, worm populations can double their biomass every 2 weeks.
For asexual reproduction, blackworms should be at least 9 mg (0.8 inches or 2 cm long). After reproduction, food ingestion ceases for up to 7 days.
|Older scholarly literature reported on the genital apparatus of Lumbriculus variegatus and a few authors mentioned sexual reproduction in laboratory cultures.
Nonetheless, even if it exists, sexually mature specimens of this species are so rare that there is no even consensus between different authors.
Blackworms as Live Food
In the aquarium hobby, blackworms have an important position in the aquatic food chain, being a major food source for fish, crabs, crayfish, and other vertebrates and invertebrates.
According to the study, blackworms contain lots of protein and meet fish nutrition guidelines for protein and essential amino acids making it a healthy and nutritious food option for the fish and other tank inhabitants.
Experiments showed that blackworms’ gross nutritional value was similar to other fish diets (such as Artemia nauplii, frozen brine shrimp, or trout chow) and made it desirable as a prey organism for conducting dietary exposure studies with fish.
|Components||Dry matter %|
Note: Another great thing about blackworms is that they do not pollute and cloud the water as many other foods do.
Supplies for Culturing Blackworms
The following supplies are needed to culture Blackworms.
- Starter culture: bloodworms
- Culture vessel: small tank or plastic container
- Substrate: pea-sized gravel
- Filtration: sponge filter
- Oxygen: air stone
- Harvesting: fish net
- Food: Spirulina or blanched vegetables
Basic Set Up for Blackworms Culture
- Add a fin layer of the substrate into the tank.
I repeat, there is no need to put a lot of substrate. It will be enough to have 0.4 inches (1 cm) deep.
- Install the sponge filter.
There are many advantages of using sponge filtration. It is cheap, simple, and safe for blackworms.
- Install the air pump.
- Add water to the tank.
There should be enough water to completely cover your filter, nothing more. In most cases, 6 – 8 inches (15 – 20 cm will be enough).
Note: You can use old water from the water changes.
- Cycle the tank (or wait at least 4 weeks) before adding the blackworms.
- Optimal temperature: 68 – 77°F (20 – 25°С)
- pH: 6.5 – 8.0
- Dissolved oxygen: 2 – 8 mg/L
- Photoperiod: 8-12 hours daily.
|Important: It is highly recommended to thoroughly rinse the blackworms before adding them to the tank. There can be a lot of gunk and even leeches.
Do that 3 – 4 times (with chemical-free water 60 – 68°F (15 – 20°С)) until the water is clear.
Check for parasites. Only after that add blackworms into the tank.
Uncycled tank: Ammonia and Blackworms
Some hobbyists may ask – can I put them in an uncycled tank?
Generally, it is not recommended to culture blackworms in an uncycled tank.
According to some experiments, the minimum concentration of unionized ammonia, which was lethal to the blackworms, was 0.2 mg/L (or 0.2 ppm).
Even though some blackworms may survive during cycling, they will not grow as fast as they should.
It really does not matter. It is possible to culture blackworms in tiny jars (1 gallon or 4 liters) as well as in huge tanks.
Unless you need a lot of blackworms, a 5 – 10 gallon tank (20 – 40 liters) will be good enough for you.
Temperature is one of the main environmental factors for culturing blackworms. Although these worms possess a high tolerance for temperature fluctuations, their optimal range is between 68 – 77°F (20 – 25°С).
Blackworms do not like too warm water. The lethal temperature for 50 % of the worms will be 80 – 86°F (27 – 30°С).
Their feeding rate slows down significantly at 50°F (10°C). Blackworms stop reproducing at 42°F (6°C).
Oxygen and Aeration:
The culture water should be aerated continuously using air stones. As I have already said, blackworms can switch to anaerobic metabolism only for a short time. They need oxygen.
Blackworms are generally found in slow or still waters because of their poor ability to swim against the current. They do not need high flow.
Experiments showed that Lumbriculus variegatus displays negative phototaxis.
Blackworms avoid light whenever it is possible. Complete darkness enhances digestion and worm growth rates. In addition, the survival rate was significantly less in chambers exposed to sunlight than in chambers held in the dark.
So, blackworms do not need lighting. Ambient light will be enough (photoperiod: 8-12 hours daily).
In laboratory experiments, scientists use brown paper as a substrate for culturing blackworms.
However, for our goals, we need small gravel from 0.1 to 0.4 inches (3 – 10 mm).
|Note: Gravel will play the most important role in culturing blackworms. It will split the worms at a better rate when we start mixing the gravel around every couple of days.|
How to Prepare Gravel
- Place the gravel into the bucket.
- Fill the bucket with tap water. The water should completely cover the gravel.
- Stir and move the gravel around (use a stick if necessary).
- Leave it in the bucket for 5 – 10 minutes. It will soften up any dust and debris that may be on the gravel.
I would recommend using sponge filters for culturing blackworms. As long as you have got the filter that works great with the size of the tank you have got you will be fine.
These filtration systems are cheap, easy to maintain and clean, provide a lot of surface area to graze on, and are absolutely safe for these worms.
Do not use filters with an impeller. Even if you use an extra pre-filter in the form of a sponge, it will not help you because blackworms love to invade a sponge! Eventually, they will get caught in the impeller.
In their natural habitat, blackworms feed on decaying vegetation and microorganisms.
Studies have shown that Lumbriculus variegatus can ingest only particles with sizes of 40–60 m, while larger particles (100–300 m) would exceed the size of its mouth.
It was also proven that food level has a very significant influence on the growth and reproduction of blackworms.
In the aquarium, blackworms will benefit the most from:
- fish food (such as Tetramin, Spirulina, etc.)
- blanched vegetables.
How much to feed Blackworms
If there is not enough food, blackworms will not grow and reproduce very well. However, if you feed them too much, you risk losing the culture because of the water quality.
Overfeeding can kill your culture before anything else!
Generally, you need to feed blackworms about 2 or 3 times a week.
Any leftovers should be removed the next day by siphoning before fresh food is added.
Note: Crush algae wafers/pills with your fingers. Powder food is better for blackworms.
Maintenance of Blackworms
Once started, the blackworm cultures require very little maintenance. Under optimal conditions, it will produce an abundant supply of worms.
- Check your water parameters. Water changes (30%) must be done every 4 – 7 days since the amount of food and bioload may significantly affect water quality.
- Check your water temperature. High temperatures are lethal for blackworms.
- Blackworms are sensitive to copper. According to the study, The LC50for Lumbriculus variegatus to copper exposure as determined was 0.45 μM.
Boosting Reproduction of Blackworms
However, in an aquarium setting we can cause blackworms to split sooner by vigorously stirring the substrate every 4-5 days to fragment the worms.
Blackworms have a very soft body that easily splits from the contact of the gravel.
After swirling, your water will get cloudy and blackworms will be ‘flying’ around the tank. Do not worry, this is OK.
Blackworms grow very quickly, thus you should have plenty of worms to harvest after a few weeks of starting the culture. This is one of the downsides – these worms do not reproduce as quickly as other commonly available live foods.
There are 3 main ways to harvest blackworms:
- Turkey baster (clean and slow)
It is almost like vac cleaning but this time we just harvest the blackworms.
- Fish net (messy and fast)
Mix the gravel in the tank. There will be lots of blackworms in the water column. Scoop them with the net.
- Sponge pieces (clean and fast)
Blackworms love to get into the sponges. Therefore, if you have a spare sponge, you can cut it into small pieces 1×1 inches (2.5×2.5 cm) and drop them in the tank with blackworms.
When you need some blackworms, just pick up one of the sponge pieces and drop it into your tank with fish.
Storing Blackworms (The Right Way)
The easiest way to store blackworms is to place them in the refrigerator (at 60°F or 15°С).
- The blackworm should be placed in a thin layer (no more than 0.4 inches or 1 cm) if they are thicker they may suffocate.
- There should not be more than 4 inches or 1 cm of water above them. Without aeration, they can drown.
- Do not cover their container completely. There should be a gas exchange, so they will be able to breathe.
- Rinse them at least once a day. Use only treated and cold water (at 60°F or 15°С).
- There is no need to feed them. Blackworms can live without food for months at the cost of their own body
Do not keep blackworms outside boxes, basements, etc. This is a bad idea.
Culturing blackworms is very easy even for a beginner aquarist. They require little attention, and the cost of setup is quite inexpensive.
Blackworms are an excellent food source for many species of fish, crabs, and crayfish irrespective of their size. They are full of protein and nutrition. You can serve these little worms to fry, juvenile, and adult fish, as well as amphibians e.g. newts, salamanders, and inverts such as crayfish, lobsters, and crabs.
Another great thing about Blackworms is that they are hardier than many of the other live foods, and do not easily die off as daphnia or brine shrimp.
So, if you have a tank or two, by culturing them yourself, you will probably never have to buy blackworms again.
|Blackworms as Live food|
|Very high nutrient content||Requires some time|
|Contain lots of vitamin and mineral supplements|
|Easy to culture|
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