January 2004. A request has been made to import three earthworm species into Tonga ( Eisenia fetida; E. andrei and Perionyx excavatus from New Zealand. The request is to import the earthworms for vermicomposting or worm compositing. The reaction of members was requested.
Some anecdotal or circumstantial information was reported from the highlands of Papua New Guinea: villagers blamed a particularly aggressive earthworm (obviously introduced following the opening up of the highlands areas to the outside world in the 1960s and 1970s) as being responsible for compacting soil. This may occur particularly in disturbed soil types (e.g., clay) where earthworm exudates dry up and harden, making cultivation with spades and hoes difficult. While the benefits according to the importers will be tempting, there is a need for caution about the planned introductions. Also, much of the concern will be environmental.
Earthworms can reportedly drastically change nutrient cycling in native forests where they do not occur naturally. It would be necessary to consider potential impacts extremely carefully (on the assumption that it is impossible to ensure containment of the species once it arrives in the country.
One indirect effect may have to do with the abundance/spread of feral pigs, as this quote demonstrates:
“Perhaps aided by a seasonally abundant and expanding carbohydrate source – the invading nonindigenous strawberry guava – and by an enhanced protein source from abundant nonindigenous earthworms, truly feral pig populations developed and spread into adjacent pristine forest.”
“The pigs were apparently attracted to bog habitats by the availability of nonindigenous earthworms, which
are probably an important protein source (Loope et al., 1991).”
Both above quotes are from the “Hawaii and the Pacific Islands” document referenced (first title on page) at:
Interactions with other species besides pigs have also been observed, e.g.:
“Interactions between the nitrogen additions by Myrica and the litter processing by earthworms are likely to exacerbate ecosystem changes in areas where Myrica is invading.”
…from abstract of:
Aplet GH (1990) Alteration of earthworm community biomass by the alien Myrica faya in Hawaii. Oecologia 82: 414-416.
…quoted from: http://leopold.wilderness.net/resapp/pdfs/vol4.pdf
Blakemore RJ Cosmopolitan Earthworms ??? an Eco-Taxonomic Guide to the Peregrine species of the World. Graduate School of Soil Ecology, Yokohama National University, Yokohama, Japan. 9th Biennial Soil Ecology Society conference, 11-14 May 2003, Palm Springs, California.
Earthworms are ubiquitous in soils that support plants and their populations often have four components: natives, exotics, translocated natives and ‘neoendemics’. Of a world fauna of nearly 5,000 known taxa, invasive exotics occurring in a region are drawn mainly from a pool of only about 100 species. These are referred to as the Cosmopolitan or Peregrine Species and comprise about 30 Lumbricidae from Europe/Middle East, 30 Oriental pheretimoids (Megascolecidae), with the remainder made up of members from about a dozen lesser families having diverse origins. Often their distribution and spread corresponds to the various migrations of human populations, but other mechanisms of transportation occur. As an ancient and major component of the soil fauna, earthworms are generally considered beneficial, or at worst benign. However, there are some reports of adverse effects of introduced species on soils, and of their potential to transmit pathogens, including Anthrax and Foot and Mouth virus.
This presentation introduces a new CD guide to the Biology, Ecology and Identification of the 100 most Common Exotic Species found around the world. Keys lead to descriptions and illustrations. Included are the commercial vermicomposting species (e.g., Eisenia fetida/andrei, Perionyx excavatus, Eudrilus eugeniae, Dendrobaena / Dendrodrilus and Pheretima spp., etc.). The guide provides an essential tool for soil ecologists anywhere, as identification is a first step to understanding and, once the exotics are recognized, then global distributions can be plotted and studies of relationships with other soil organisms and to other soil processes can progress.
Another useful contribution was received from the National Institute of Water & Atmospheric Research, Wellington, New Zealand.
First, these species are all alien to New Zealand; second, they are invasive, human-settlement-associated species. That’s why they’re in so many countries already! Eisenia fetida is the manure worm, used in bulk decomposition of wastes and sludges. It will likely spread to all areas of settlement if iintroduced.
The Indian Blue, Perionyx excavatus, is thought to be a comparatively recent arrival in New Zealand, but is reported to be spreading rapidly (via wormfarmers!). There is a lot of info on the Internet on vermiculture. But it does not take consideration of invasiveness of particular species released into new areas, or the consequences thereof … rather it is interested in solutions to waste management problems and the economics involved. For instance this recent report: http://www.rirdc.gov.au/reports/NAP/03-085.pdf.
An efficient worms used in vermi-composting are the Californian red worms Esenia foetida.
A first step might well be to establish what earthworm species are in Tonga already. Crop & Food Research, New Zealand, might know or be able to find out.