Yuck, what is that stuff?

Most of the colours encountered in nature (at least here in Britain) are sombre and subdued. Rightly so, you may say, particularly when you think of a damp piece of woodland towards the end of a rather warm autumn. Those spots of bright colour, the hideous primary yellows and garish reds, are almost invariably pieces of litter, left by some mindless ruffian happy to despoil our beloved countryside. However, there have been times when my eye has been drawn to some almost luminous patch of colour which is natural in origin. These are the fruiting bodies of yellow slime moulds, crawling imperceptibly across the woodland floor.

Slime moulds can be pretty revolting to look at and, at times, seem almost alien in origin. Little studied, they have sometimes been classified alongside fungi, yet other authors have lumped them with the protozoa (simple single-celled organisms). However you view them, it is fair to say that these overlooked creatures are to be found just about everywhere on the planet (with some forms seemingly able to live submerged for several at a time). The part of their life cycle that we are most likely to encounter is the plasmodium; the slimy, almost jelly-like, stage which is mobile and gives rise to fruiting bodies; it is these fruiting bodies that are suggestive of a fungus. Most slime moulds produce a plasmodium that is just one or two centimetres across and able to travel up to 10 centimetres a day. Some of the largest ones can reach two metres in diameter and may weigh over a kilogram. Alan Feest, quite a fan of slime moulds, once related how he had stumbled across a large slime mould, draped over a tree stump and giving the appearance of somebody having tipped a can of whitewash over the stump. When he returned the next day, the slime mould had moved off part of the stump and onto a neighbouring bramble, leaving a trail of slime behind!

Fruiting slime moulds produce spores which, catching the wind, disperse over large distances. The spores are remarkably robust and may survive for many decades before ‘germinating’ or ‘hatching’ (I am not sure which is the more appropriate term) into a simple single-celled stage. This feeds on bacteria and grows, developing thread-like appendages in wet conditions (these help it to move around) but retreating into a cyst when it becomes too dry. At some point the unicellular stage develops into a plasmodium, creeps about and then fruits. This complex life-cycle, and the fact that these are organisms that blur the line between animals and fungi, make slime moulds rather special and, most probably, worthy of our attention, despite their odd appearance.