The jaw-dropping tail-dropping earthworms

Author

Frank Ashwood
Earthworm tail dropping
Bimastos rubidus (Poland)

Last September I attended an earthworm research conference organised by Earthworm Research Groups from the University of Central Lancashire (UCLan) and University of Rzeszow. The event took place in the Bieszczady National Park in the Polish Carpathian Mountains, a part of the Carpathian basin - which is home to around 100 earthworm species, of which roughly 40% are found no-where else in the world [1]. We had the wonderful opportunity to visit Carpathian beech forests and there I was introduced to a revelation… tail-dropping (or natural amputation, scientifically known as ‘autotomy’) in earthworms!

UK earthworm tail dropping
Aporrectodea longa (UK). Photo courtesy of Emma Sherlock.

I was amazed when I picked up a small epigeic earthworm (probably the ‘bank/tree worm’ Bimastos rubidus according to my Polish hosts) which promptly dropped its tail and tried to escape, whilst its lost appendage attention-seekingly twitched and wriggled in my hand. This behavior is perhaps best known as a self-defense mechanism in reptiles, but interestingly tropical earthworms are known to sacrifice their tails to predatory ants, which have learned where best to bite the earthworms to encourage autotomy [2]. Lost segments are regenerated over time, leaving the earthworms alive, and conveniently providing the ants with a sustainable food source. It should be noted that, and to put an old myth to bed, when an earthworm is cut in half only the head end survives! [3]

Earthworm tail dropping
Aporrectodea caliginosa (UK)

All this left me wondering whether any of our native UK earthworms drop their tails. It appears that a number of earthworm species are capable of doing so, including the composting species Eisenia andrei and the soil-dwelling ‘grey worm’ Aporrectodea caliginosa [4]. In fact, at a recent FSC earthworm residential training course we found a rather sickly-looking A. caliginosa which dropped its tail in the hand of a student! Speaking with Emma Sherlock, curator of Annelids at the Natural History Museum, it seems that the deep-burrowing ‘black-headed worm’ Aporrectodea longa is also capable of dropping rear segments, as shown in the photo below. And earthworms don’t only amputate their tails to avoid

predators; it’s also a known immune response process by which they remove large pathogens that are accumulated in their rear segments [5].

As for me, I’d like to learn more about which other earthworm species are capable of autotomy, and the natural conditions which make them do it – who knows what weird and wonderful things we might learn!

 

References/further reading

[1]         C. Csuzdi, V. V. Pop, A.A. Pop. (2011). The earthworm fauna of the Carpathian Basin with new records and description of three new species (Oligochaeta: Lumbricidae), Zool. Anz. 250 2–18.

[2]         A. Dejean, B. Schatz, J. Orivel, G. Beugnon. (1999). Prey capture behavior of Psalidomyrmex procerus (Formicidae: Ponerinae), a specialist predator of earthworms (Annelida), Sociobiology. 34, 545–554. doi:10.1103/PhysRevD.84.055013.

[3]         M. Kocinski, V. Takacs, L. Molnar, A.J. Morgan, J. Bigaj, B. Plytycz. (2016). Experimental induction of autotomy in two potential model lumbricid earthworms eisenia andrei and aporrectodea caliginosa, Invertebr. Surviv. J. 13.

[4]         M. Bilej, P. Procházková, M. Šilerová, R. Josková. (2010). Earthworm immunity. In: Söderhäll K (ed) Invertebrate immunity. Springer, New York, pp 66–79

[5]         G. R. Cameron. (1932). Inflammation in earthworms. J. Pathol. Bacteriol. 35: 933–973.