Leeches

Leeches arouse, almost universally, a “Yuck!” response out of all proportion to the pain and suffering they cause.

Our attitudes to small wildlife reflect our upbringing and experience and I’m constantly intrigued (and sometimes very quietly amused) by them. Most people I know “love wildlife” but only up to a point. They might love all mammals and birds but not reptiles, for instance, or like small lizards but not the big ones. Most of them love butterflies but many are not at all keen on spiders (I agree they are not usually so pretty but I like them just as much) – and then we reach the problematic types: flies, fleas, ticks, mozzies and of course leeches.

What is a leech?

We also tend to know very little about leeches. What kind of animal are they? They are obviously not vertebrates but they can’t be insects because they haven’t got six legs, so what what are they most closely related to?

The answer is worms – earthworms, in fact. As Wikipedia says:

Leeches are segmented parasitic or predatory worms that belong to the phylum Annelida and comprise the subclass Hirudinea. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular, segmented bodies that can lengthen and contract. Both groups are hermaphrodites and have a clitellum, but leeches typically differ from the oligochaetes in having suckers at both ends and in having ring markings that do not correspond with their internal segmentation. The body is muscular and relatively solid…

Most of them live in water but the ones we know best live in wet terrestrial habitats such as rainforests.

Leeches at Forgotten Falls

As regular readers may have guessed, these reflections are the result of meeting several leeches on the bushwalk I described in my previous post, refreshing my personal experience of their feeding habits (yes, I was bled) and giving me opportunities during our lunch break to watch and photograph a couple.

All of our rainforest leeches seem to be in the genus Chtonobdella (two others occur in southern states but not here) but it’s hard to know which species. This gallery on ALA shows some of the diversity; I can only say that all of the leeches I looked at last weekend had the same two yellow stripes but this one at Wallaman Falls a few years ago didn’t:

leech
Leech at Wallaman Falls

Removal

Unlike ticks, leeches do not burrow into the skin nor leave a poisonous head in the wound. Despite this, there are many myths about removing them. The simplest way is with salt: a shake onto the body will make most of them quickly drop off. Tea-tree oil or vinegar dabbed onto the body are just as effective, as are insect repellent and insecticide. Otherwise, simply pull them off.

Or you could just leave your uninvited guest there to drink its fill and drop off when it is ready. It’s a radical suggestion, I know, but there are, in fact, very rare cases in which this is the best thing to do, as David Rentz reports at the end of this blog post.

Some people suggest dabbing a little tea-tree oil onto the open wound to prevent infection. While leeches are not known to spread disease, any open wound in wet muddy conditions invites bacterial attack.

Points to ponder

  • Do they hurt us or poison us? Very, very rarely.
  • Are they useful? Yes, sometimes.
  • Are they slimy? Yes (they can’t afford to dry out).
  • Were we taught that slimy = bad? Very likely.
  • Were we taught that they are yucky? I’m afraid so.
  • Can we overcome that conditioning? I hope so.

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