The great Charles Darwin had a weakness for earthworms. On and off for 40 years he studied these creatures, observed, measured, and counted them and is known to have played his bassoon to them to determine if they were deaf. In 1881 he finally published his earthworm results in a book, in which, perhaps surprisingly, he even credited earthworms with intelligence and benevolence.
Darwin found on average 700 worms per m2, equivalent to 250 g, in his garden; he demonstrated how efficiently earthworms ploughed, aerated, and fertilized the soil, and his research prepared the ground for a discovery not long ago that earthworms lock up approximately 560 kg of carbon per hectare of soil per year in the form of calcite. What Darwin would have delighted, is that India now has probably the largest earthworm breeding centre in the world. In North Delhi, 15 million earthworms turn garbage in the form of human excreta, cow dung, fallen leaves and kitchen wastes into natural manure. The venture is Mr. Yashpal Suhag’s brain child and developed out of his association with the famous Earthworm Research Institute in Pune (India).
What Darwin presumably did not know at his time was that a little alien, luminescent species by the name of Microscolex phosphoreus, originally from Argentina, was slowly establishing itself on the British Isles and elsewhere in Europe. First seen in a greenhouse in France in 1835, it was reported from Ireland and some bogs near Liverpool between 1854 and 1862 and in 1928 had arrived in Poland. It can survive winter temperatures down to -20ºC and has been reported to distract players on golf courses. (Don’t ask me what golfers would do on a golf course at night, the only time one can see the worms’ bright glow when one of these critters is stepped on or attacked by beetles or centipedes.) Anyway, Darwin certainly knew that some earthworms could live for many years. A mature and fully extended Australian Gippsland earthworm (Megascolides australis) can reach 3 m in length and, like other large species in South America, New Zealand and elsewhere, can probably attain a life span of 50 years.
Earthworms occur everywhere on Earth with the exception of Antarctica. Luminescent species, apart from Microscolex phosphoreus mentioned earlier, have been reported from several localities in North- and South America, Africa, Asia, Australia and New Zealand and usually belong to the families Octochaetidae, Megascolecidae, and Acanthodrilidae. In Japan, the light-producing Pontodrilus matsushimensis, which is a true earthworm and not a polychaet, was first recorded from the sea-shore near Yokohama in 1938, but is now known to be widespread in Asia. Although it did not surprise researchers when in North America light-producing earthworms of the genera Pontodrilus and Diplocardia were discovered (and subsequently thoroughly investigated), it was quite a sensation when Russian biologists recently described some 15-20 mm long, light-producing earthworms of the genus Fridericia from Siberia. What remains the greatest puzzle is why, on a global scale, only very few species of earthworms produce light when attacked.
In New Zealand I have fed with the permission of Eric Fox (the Director of Otorohanga’s Kiwi House) a brightly luminescent worm to a kiwi bird (which did not hesitate to gobble up this wriggly morcel); others have observed chickens to devour luminescent worms. What’s the point of secreting some luminescent slime if it does not prevent the worm from being eaten? And talking about earthworms as food: tribal people of the Orinoco Basin in South America have been filmed collecting, preparing, and eating earthworms, irrespective if they glowed or not. The worms may be tasty, but I don’t think that Darwin would have eaten any, for he loved his earthworms much too much.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2020.
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