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Hotham's blue worm is a wet weather find

Posted 14 November, 2018

Spring brings wet weather to the slopes and valleys of Hotham, and if you're lucky you might see one of our most surprising small residents, the Blue Planarian (flatworm), also known as Caenoplana coerulea.

Planarians evolved quite a long time ago, and have a central nervous system including a well-organized brain with many types of neurons. They live in the soil and are known to respond to light by trying to avoid it, but when it rains, they don't have much choice.

The Blue Planarian is not rare, but it doesn't tend to show itself unless it has been forced out by water-logged soil, or if it's on the prowl for something to eat. Yes, it's a predator, so it's fortunate that it's only about 6 centimetres in length. 

Unlike normal soil worms, the Blue Planarian moves on a slime trail like slugs and snails, so if you watch it move you can see it flatten out a little as it moves. 

It has quite an appetite, and feasts on woodlice, millipedes and earwigs, as well as on land snails. 

Martyn Robinson, from the Australian Museum, writes entertainingly about the Blue Planarian in his blog:

These terrestrial planarians are related to the flatworms much talked about in biology lessons as ‘super regenerators’ – chopped into tiny pieces each has a good chance of regenerating into a new worm; slit the head lengthways and the worm will grow two heads, and so on. These land-dwelling relatives are larger than those in the biology lab but just as able – quite a few species seem to reproduce by fragmentation and subsequent regeneration.

Interestingly they are all predators, and the wet weather brings them out hunting. Blue Planarians use their viscous slime trails to trap small animals like slaters and millipedes. The planarian cruises along old trails and drowns any victims in slime before sucking out their insides with a mouth located on its belly. If this all sounds a bit ugly, consider that the planarian digestive system has only one orifice – all wastes must exit the same way the food went in, via the mouth.

It comes in a range of colours, despite being called 'Blue' (how Australian can you get!), but the bright blue version is currently being seen in Swindlers Valley, so keep your eyes peeled if you are bushwalking after rainy weather.

For information about bushwalking at Mt Hotham, check our Hiking page on this website.

Photo: Naomi Monk, Mt Hotham Alpine Resort Management Board

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