Worms do not, contrary to popular belief, mate between species.
They can’t because in most cases the sexual organs of different species don’t correlate, so that cross-fertilisation simply cannot occur.
Additionally, differing species are genetically incompatible. For a successful mating to occur, the two worms need to be not only of the same specie but ideally also of the same size. In worms of differing sizes, because the positions of the sexual organs will not match, while sperm may be ejected by one worm it may not find the other’s storage ducts. If cross-fertilisation were possible, in the millions of years worms have been active on this planet, surely by now cross-breeding would have resulted in only one species, spread throughout the world.
They are no known hybrids or crossbreeds, either as a species or eco-type. Instead, the species throughout the world number some 3,500 and, if anything, apart from extinction of some species through destruction of habitat, this number is increasing rather than diminishing because of the development of ecotypes.
An eco-type is a natural variation which adapts more readily to its environment than others of its species, and so thrives and develops better than its parents and siblings. Ultimately it becomes a recognisable sub-species and dominates in its own particular area. An outstanding Australian example of an eco-type is the giant Gippsland worm,. Megascolides australis. Bouche postulated that when Australia broke from Gondwanaland, about 150 million years ago, it was populated by worms mainly of the family Megascolecidae.
If you were to look at a world map showing the locations of Megascolidae, you would see them confined to Australia and neighbouring Asia, which could support this (unpopular) theory. (If the Bouche theory is correct, then the `Gondwanaland connection’ could be the basis of an explanation for the close physical resemblance and possible relationship between Spenceriella spp.. and P. excavatus.)
In the main, our Australian Megascolecid worms are usually from 200 mm to 450 mm long, but M. australis encountered conditions which fostered a growth far in excess of its relations, reaching a length of 1500 mm. (An alternative theory is that they were once quite widespread, but started to die off for various reasons, and the Bass area represents the last remaining bastion.) All attempts to cultivate this worm in an environment outside the Bass area of Gippsland have failed.
There is photographic evidence of the Bass worm as long as 3000 mm or more, being supported in the hands of three or four men. However, it seems that these worm hunters were trying to make a good story even better and not allowing facts to interfere. Close examination of the photograph shows this extraordinarily long worm to have a mouth at each end!
Hermaphrodites
The act of reproduction varies considerably between species of worms, as does the frequency and the number of young produced. However, all worms are hermaphrodites (they possess both male and female organs), and each mating partner produces an egg (which is sometimes called a pod, more usually a capsule). Some actually have the ability to reproduce without the need of a partner, being able to fertilise themselves successfully. This is known as parthenogenetic reproduction and a number of species in Australia can do this. Some parthenogenetic worms may not always use this ability, but will couple with a mate occasionally or frequently.
Of the three species we concentrate on in this article, the Reds and Tigers always require two worms to reproduce. The Blues can, and do, do it on their own. I have been cultivating Blues for over twelve months now and have never seen two worms coupling, whereas it is a frequent sight with Reds and Tigers. It seems most likely that Blues are permanently parthenogenetic.
A particular advantage of parthenogenesis is that the rule ‘to meet is to mate’ does not apply. Once the young worm achieves sexual maturity it can start reproducing without having to find another worm which must be not only of the same species but also of the same size (and similarly inclined). This is one of the reasons Blues are such prolific breeders. No time is wasted.
It was first identified in Australia in my worm beds at Maryborough, the furthest point south at which it was (now) known to survive (and thrive) but clearly it has been around in Australia for many years before it was noticed as a separate species. It may be that P excavatus has found conditions in Australia so different from those of Malaysia, that perhaps we are seeing the development of an eco-type. Many would disagree with this speculation, but there has to be more in the explanation of the differences of the ‘Kale’ and ‘Murphy’ P. excavatus than feed.
In the time that it has been here (and nobody knows how long that is) in adapting to Australia’s harsh climatic environment of droughts, followed by short periods of wet, Blues seem to have rewritten the rules to ensure perpetuation of the species. They can hatch, develop and reproduce in the short time available before the soil dries out again, leaving capsules which will hatch when they are moistened by the next rains. They also don’t care what they eat. They are real optimists, and can be found in nutrient-poor soils as well as in manures, which are nutrient-rich. In this, they are quite different from indigenous species.
