The proper species must be present in the garden and, of course, in the cultures introduced from commercial sources. There are a number of earthworm species that occur in European and American gardens, but only two are important. One of these is Lumbricus terrestris, a dark red species found in soils that have a high organic content; the other is Allolobophora calignosa, a grayish-pink species which does not require quite as much organic matter to survive.
In both species, the body is made up of interlocking segments, interrupted about one third the way down by a smooth area known as the girdle.
Since these two species are the ones which propagate most readily in ordinary garden soils, one might reasonably expect to find one or the other in cultures supplied by commercial earthworm farmers. This is not the case. I have never found either species in the cans or packages supplied by earthworm farms.
The worm cultures used for worm propagating at such farms are usually mixed with large amounts of protein compounds and organic matter. As protein breaks down, it passes through a stage where ammonia is released. Ammonia is harmful to most earthworms and
may even kill the two species already mentioned. For this reason, the earthworm farmer propagates only the manure worm, Eisenia foetida, which is capable of surviving and propagating in the presence of ammonia. Unfortunately, this one is incapable of surviving in clay or loam soils unless these have been freshly manured. As a result, about the only place they will survive in the average garden is in the compost heap. Directions accompanying shipments of worms usually recommend placing them there.
All earthworms (with the exception of tropical species outside the scope of this book) must have soils that are high in both organic matter and moisture, but the manure worm has the highest requirements of all in this respect.
As for the hybrid worms offered by advertisers in organic gardening publications, these may exist but I have not seen any hybrids which were recognized by taxonomists familiar with these creatures. Species of earthworms tend to remain in special habitats so that opportunities for crossing are limited between species within the same genus.
Most earthworms are hermaphrodites, so that, in mating, both individuals fertilize each other. Since they live in habitats of a single species as a rule, this cuts chances for hybridity in half, even if it were possible. In other species, parthenogenesis eliminates crossing altogether