Earthworms and Black Worms

Any number of worm species may be readily cultured in captivity or purchased for use as food for your fish and invertebrates. All provide excellent nutrition for your animals, especially if the worms are fed a nutritious diet before being used.


Nearly all predatory fish and invertebrates go into a feeding frenzy when presented with earthworms, quite an unusual phenomenon considering that earthworms are basically terrestrial creatures. Many aquarists have had excellent results when using earthworms as the major portion of the diet of large freshwater fish such as bullhead catfish and invertebrates such as crayfish. In one study, a nutritional analysis of earthworms showed that they provide beneficial levels of Vitamin E and Vitamin A for a wide variety of aquatic creatures.

Using Earthworms

Earthworms of the species Lumbricus terrestris and a number of others may be broken into small pieces to provide appropriately sized meals for nearly any sized animal. The larger species, often called “nightcrawlers,” are substantial enough to tempt even large fish such as adult oscars and other cichlids.

Although earthworms can be broken into pieces so as to be readily swallowed by your smaller pets, a whole, small earthworm will provide more complete nutrition than will a small piece of a larger worm. Therefore, you may wish to purchase earthworms in various sizes or maintain a breeding colony of this very important food animal.

Uneaten earthworms will remain alive in aerated freshwater for up to eight hours, but they decompose rapidly upon death. They may also be fed to marine animals, but be aware that earthworms die and decay rapidly in saltwater.

Obtaining Earthworms

Earthworms may be purchased at bait stores and some pet stores, or ordered in large quantities from commercial breeders (check the classified ad sections of magazines or publications devoted to aquariums or to the keeping of reptiles and amphibians as pets). Earthworms are, however, such a useful food item for so many creatures that you may wish to establish a breeding colony. The only drawback to this endeavor is that earthworms are, in general, fairly intolerant of warm temperatures and so are best raised in a cool basement or a similar area. Earthworms that are purchased and stored for later use do best when kept in a refrigerator.

Raising Earthworms

Earthworms can be easily cultured in a garbage can or similar container filled with alternating layers of good-quality soil and dead leaves. The earthworms will consume the leaves as well as tropical fish food flakes, vegetables, oatmeal, cornmeal, and breadcrumbs. Collection of the worms can be simplified by feeding them on the surface of the soil, below a layer of damp burlap.

Earthworms consume large amounts of soil while feeding and thus likely take in pollutants, pesticides, and other harmful substances that may be present in the earth. Therefore, wild-caught earthworms should be used with caution. You may wish to consider purchasing your earthworms from commercial farms rather than collecting them.

Black Worms

Black worms are small, aquatic relatives of earthworms and are readily available in the pet trade. They should be stored in a refrigerator, where they will live for at least two weeks if the water is changed daily. To change the water, run cold tap water into the container so as to agitate the worms, which tend to clump together. Pour off the excess water along with the dead worms, which, conveniently, float after being stirred up by the new water.

Using Black Worms

Black worms will live well in freshwater aquariums, where they burrow into the substrate and provide foraging opportunities for bottom dwellers such as catfish, spiny eels, crayfish, and other such animals. In fact, many aquarists “seed” their tanks with black worms so as to keep their animals busy and to provide for interesting observations.

Black worms are readily accepted by nearly all fish and invertebrates that consume live prey. They are an excellent food source for elephantnosed mormyrids, Gnathomenus petersi, and other narrow mouthed specialists. The worms are also excellent scavengers, burrowing under rocks and deep into the substrate to consume uneaten food and wastes.

Black worms tend to clump together, a habit that often results in one animal obtaining a lion's share of the meal. To prevent this, you can purchase a stationary or floating worm feeder. These handy devices dispense individual worms through tiny holes, thereby allowing a greater number of animals to feed at one time. Worm feeders are also useful when feeding animals that may not be able to extract the black worms from the substrate of the aquarium.

Tubifex worms, which superficially resemble black worms, should not be used as a food for your pets. Formally a pet trade staple, they are harvested from heavily polluted waters and have been implicated in the intestinal disorders of fish and in human skin infections. Fortunately, most pet stores had replaced tubifex with black worms, but question the store's employees if you are unsure.

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