Thursday, 8 February 2007

Centipedes shake a leg

Rooting about the other afternoon amongst some fallen timber, I disturbed a veritable mass of centipedes. Each was just less than three centimetres in length, rich chestnut brown in colour and equipped with sufficient legs to exhibit a substantial turn of speed. No sooner had I registered the presence of this throng of centipedes than they had erupted in all directions fleeing from my intrusion. I have always been a little wary of centipedes; a childhood trait that I have never quite managed to overcome. As with so many childhood fears this one is unfounded, since centipedes only rarely bite humans and even when they do, the sensation is reputed to be little worse than that delivered by a stinging nettle. In fact, centipedes are overwhelmingly beneficial. They are fearsome predators of slugs and insects larvae, making them a true friend of any gardener. While their bite has little effect on us, the powerful poison it delivers is more than adequate to overpower a range of invertebrate prey.

So far, more than 50 species have been recorded in Britain, belonging to two main classes of centipede. First there are the “runners”, surface-active predators like those I had uncovered in the timber. Then there are the “crawlers”, subterranean species that make a worm-like living within the spaces that form between particles of soil.  Although the name centipede means “one hundred feet”, many species have fewer than this, while some have more. In fact, some species hatch from their egg with just four pairs of legs, gaining more pairs with each of the moults they must undergo before reaching adulthood. One of our most familiar species starts life with seven pairs of legs and ends up with 15 pairs as an adult. The species are equally variable in their behaviour. In some species an adult female will show a high degree of care for her brood of youngsters, wrapping her body around them to defend them from predators. Other species simply abandon their eggs and leave the resulting young to take their chances.

Being long and thin has its disadvantages and, with the jaws positioned right at the front, some of our longer centipedes are vulnerable to attack from the sides or the rear. To overcome this threat, some species exude a fluid from their back legs if attacked. This fluid is distasteful to would-be predators like ants and they soon abandon their attack. Other species, notably the soil-dwelling crawlers, can secrete copious amounts of sticky glue from glands along their flanks. This glue is sufficiently strong to bind together the jaws of a predatory beetle for several hours, providing more than enough time for the centipede to make good its escape. 

No comments:

Post a Comment