Tuesday, September 3, 2013

Getting a grip..

We've got three black compost bins in the garden that recycle most of the garden waste and all of the plant-based leftovers from the kitchen, so they provide a constant source of compost for the soil. The animals in the bins that do much of the recycling work are these brandling worms Eisenia foetida, aka tiger worms, aka European nightcrawlers.

A curious feature of these worms, apart from their rather attractive tiger stripes, is that they often climb the sides of the compost bins and can easily scale vertical surfaces, often attaching themselves to the inside of the bin lids. 

If you take a look at the next picture you can see how they climb .........

Each segment of an oligochaete worm like this bears stiff, retractable bristles called chaetae, which are the little white projections that you can see in the picture above. The moisture on the worm's body makes it naturally slightly sticky, but it's these bristles that grip surfaces as it alternately extends and contracts its body as it moves forward. 

In the picture above the worm is contracting the longitudinal muscles in the front part of its body so that it shortens and becomes fatter, dragging forward the segments behind whose chaetae have temporarily retracted. 

Next the chaetae on the forward segments will retract as their circular muscles squeeze them and make them longer and thinner, stretching forward, while the bristles in the segments behind will extend their chaetae to provide grip.

If you place one of these worms (or a common earthworm) on a sheet of paper and listen carefully you can hear the scratching of the chaetae on the paper as the worm wriggles.

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