12 January 2006

One hell of a big worm

How is this for backyard composting? Photo from Age.

A month-old news item from the Australian newspaper Age (via Worms of Endearment) is about the relocation of a colony of the Giant Gippsland Earthworm (Megascolides australis), living in the path of a planned road. These evolutionary marvels, endemic to Australia, are unfortunately threatened because of degradation and loss of their habitats.

Megascolides australis (phylum Annelida) is truly a giant among terrestrial invertebrates; according to this document lengths of adults average under 1 m. Reading about this earthworm reminded me of another month-old item, the 330 million-year old fossil trackway of a huge water scorpion that had been discovered in Scotland1. The author estimated that the water scorpion that had laid the tracks was about 1.6 m long and 1 m wide. What is more interesting is that the animal was apparently walking on land. Assuming that the identification of the animal and the estimate of its size are correct, this finding implies that arthropods much larger than the extant terrestrial species can survive on land at least temporarily. But as opposed to giant annelids, giant permanently terrestrial arthropods never seem to have evolved.

This may be because of difficulties associated with water conservation. The body shapes worms, giant or not, allow them to easily burrow into damp soil where they are protected from desiccation. Large arthropods, on the other hand, would have difficulty burrowing deep unless they evolved more worm-like bodies.

1. Whyte, M.A. 2005. A gigantic fossil arthropod trackway. Nature 438:576.

1 comment:

Anonymous said...

holy croud thats a worm? i swear that was an ugly looking snake not that any snake is pretty.i only knew about these things because we're doing dissection with earthworms in class in gr.8. well thanks 4 the pic......................................................... holy that things is huge, compare to the earthworms i've seen.