Bloodworms are larvae of the mosquito-like midge family Chironomidae. Almost all chironomids have aquatic larval and pupal stages. They have a worldwide distribution and occur in a wide range of aquatic habitats from fast flowing to completely still and stagnant, and in waters that range from fresh to saline. There may be more than 5000 species but only a small number have been formally identified. There is little difficulty in recognizing the larvae; they are small, distinctly segmented worm-like animals. Although, they are not a true worm due to their exoskeleton and small-clawed legs. Their color is variable; some common ones are white, green, yellow, or deep red. The latter is due to the presence of the red pigment, erythrocruorin in the blood of the larvae, the presence of which is of respiratory advantage in waters with low levels of dissolved oxygen (stagnant pools). Some are also transparent and are commonly known as glassworms. However, only those that contain erythrocruorin are red and hence the common name “bloodworm. In some countries, they are also known as red mosquito larvae.

Food value to fish

Chironomid larvae and pupae have a relatively high protein content with high digestibility and constitute one of the staple food items of many fishes in their natural environment. Chemical analysis (% of dry weight) shows that bloodworms contain 71 to 93.6% moisture, 47.7 to 62.5% protein, 4.9 to 28.6% fat, 2.3 to 21% ash, and 4 to 23% carbohydrates. They are also a good source of iron for the fish since they contain hemoglobin. Bloodworms are commonly used as a live or frozen food source for aquarium fish culture. Almost all fishes will greedily devour them when they are offered. Research has found that most fishes when provided with bloodworms as a supplementary food item have better growth and spawning rates. Frozen bloodworms could be used as a substitute for live tubificids as they have a comparable protein level.

Life cycle

Chironomidae go through a complete metamorphosis in their life cycle, egg, larva, pupa, and winged adult midge. Each stage having different characteristics. After mating in flight the female releases the eggs while skimming the water surface. The eggs sink to the bottom where, under tropical conditions, they hatch in 24 to 48 hours into the next stage – the larva or aquatic stage. The newly hatched larvae are not more than 1 mm long but they can measure up to 10 to 25 mm when they reach the last stage of the larval period. The larval stage can last from less than 2 weeks up to 7 weeks depending on temperature. Each larva molts four times before it reaches the pupal stage. This stage of the chironomid forms a large part of the natural diet of many fish as they leave the larval tube and actively swim to the surface of the water. Those that reach the surface emerge into flying adults after a few hours and immediately fly off to mate, living only a few hours or days. The adults do not feed during their adult existence and mating normally occurs during the night. The entire life cycle can be completed in 2 weeks, although it is common for the life cycle to take longer to complete.

Where are they found

Midge larvae can be found in most waters with muddy bottoms. They occur in great numbers in ponds, swamps, and streams, usually 3 to 13 feet deep. Natural breeding sites for chironomid midges are diminishing due to urbanization, land clearing and other changes to much of the natural environment. However, they are abundant in wastewater channels, sewage treatment and settlement ponds, and other man-made water systems. It is these breeding areas that cause a variety of nuisance problems and public health agencies regularly spray these areas with insecticides to control their population and distribution.

Collecting them live

If you wish to collect bloodworms the best time to catch them in large numbers is during the night when the larvae leave their self-made tubes and when the dissolved oxygen at the bottom of the water is low. They can be caught easily using small mesh netting. Bloodworms can also be obtained by sieving the mud on the spot. The larvae and the coarse particles of detritus will remain in the sieve and then shaken into a bucket filled with water. After a while, the larvae will swim to the surface where they can be collected with a net. Bloodworms are mainly collected from natural habitats, thus their quality could be affected by heavy metal contamination, infectious diseases, and parasites. Attempts to propagate bloodworms have been carried out in many countries without much success. The major problem is the inability to induce swarming and mating of the chironomid midges in captivity. However, there is now some successful cultivation of bloodworms in Southeast Asia. The larvae attain a size suitable for feeding purposes in 16-20 days. Their growth and development are influenced by numerous environmental factors including temperature, photoperiod, and food availability. Remarks.

Problems when feeding to fish

A note of caution here on feeding the larger imported frozen bloodworm. These worms have a chitinous exoskeleton and numerous bristles that are indigestible for fishes with small intestinal apertures. The meaty portion of the worm is readily processed, but the hard bits remain and clog up the stomach in an immovable mass. Be careful not to feed your discus, rainbows and some tetras on the larger bloodworms.

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