Wednesday, November 11, 2009

Fauna less loved: bloodsuckers.

I often wax lyrical in this blog about the flora and fauna in our garden, but some species are less welcome than others. Here are a couple of invertebrates that can make gardening a little hazardous.

This is a paralysis tick, Ixodes holocyclus. It's only tiny when it hasn't been feeding: this specimen is only 1.5mm in body length.When they're engorged with blood, they increase in size by many times.

Ixodes holocyclus

Ixodes holocyclus is indigenous to the east coast of Australia, and its food source is primarily the blood of marsupials such as wallabies, bandicoots and possums. Domestic cats and dogs are particularly vulnerable to them in bushland areas, and without treatment can die. Human fatalities have become far less common since the development of an anti-toxin.A couple of months ago, a paralysis tick made its way into my bra, and injected me with its toxin. By next day, the inflammation on my breast (lovely soft flesh--a tick's delight!) was the size of a saucer, raised, hot and very painful. It took a course of antibiotics, antihistamines, steroid cream and many sleepless nights before it subsided.

Ticks are in the class Arachnida, like spiders and scorpions, and thus have eight legs.

Another bloodsucker frequenting our garden is the leech. The species below is (most likely) the Australian Land Leech, Gnatbobdellida libbata, which has evolved to live out of water, and becomes active after rain.


While waiting for prey, the leech anchors itself by its posterior sucker and raises its body up. It senses potential victims by vibrations and chemical sensing, and attaches to the skin by its mouth. Then it injects anticoagulants and histamines to stop the blood from clotting and allow it to flow freely into the leech. Amazingly, it's easy to miss that a leech has attached to you. It's only after it's full and drops off to digest your precious bodily fluids, that you notice the itch---and the blood freely pouring out of the wound. If you're prone to allergies, like me, a nasty hot, itchy welt can develop.

Much as I loathe their effect, I do have a grudging admiration for leeches. They mark a significant evolutionary development from less derived species, because their body segmentation improves their mobility--something very evident when you watch one weaving through the air after it's sensed your presence. Leeches are hermaphrodites, and cross-fertilise during sex. In the phylum Annelida, they are related to common garden worms, but most of their near relatives are marine.

Next time, friendlier species, I promise!


Bjørn Østman said...

Fascinating. Sorry to hear about the tick bite.

I remember climbing/hiking up a mountain in Japan during ht wet season. There were leeches all over on the path, and I was freaked out. Funny thing was that trying to kill them (sorry, I was really freaked out) only got their attention and they tried even harder to find skin. Great example of how a simple strategy for feeding works even though it would seem sensible to be able to scamper away when someone is trying to kill you.

Margaret said...

I can understand that reaction to them, Bjorn. I've seen otherwise completely sane scientists do a weird shaking dance in a rainforest, trying to deter the leeches surrounding them!

The strategy is interesting, isn't it? Of course, they're not that easy to kill. They have tough skin, and because they're so flexible, they'll often survive even a stomp.

Unknown said...

Hi Margaret, I have been searching for information on the Australia land leech as we have a garden including some temperate rain forest in the Blue Mts off Bells Line of Road. We have leeches active from Jan-Feb each year and this year because of the deluge of rain during Jan they are particularly present! It is hard to avoid them while gardening or rain forest walking without suiting up like an astronaut. A very new fashion look even for a keen gardener!
I have been researching about their life cycle and natural predators hoping that the native wildlife here might contribute to keeping the leech numbers down. Apparently the Pitta feeds leeches to their young (but this may only be the northern hemisphere Pitta?) We have many birds including the lyrebird, and the more common magpie, robin and kurrawong etc in the garden and they all love grubbing for food at ground level and I am hoping that they all love leeches for breakfast although I cannot find anything on the web (so far) that really details the leech predator. Do you know anything about the leech predators?

Margaret said...

Hi Annie,

I don't know of any specific predators off-hand, sorry. I think though that the birds you mention would indeed predate on them. We too have lyrebirds, as well as brush-turkeys, and given the enthusiasm with which they dig through the leaf litter, I'm sure they're regularly encountering them and I can't think why they wouldn't be eating them.

If I find anything more, I'll post it here.

(Incidentally, I was just reading that the recent rains have also brought out a bit of a plague of funnel-webs across Sydney and the Mountains.... It's wonderful for the gardens, but less wonderful for our sanity!)



Unknown said...

Hi Margaret, I was up at Bonnie Doon (Lake Eildon) over the weekend. I was fishing along the bank and being a hot day I was wading in the water as well. After a couple of hours I felt a small pinch on the top of my foot and there was a really big yellow striped leech hanging on. It was the size of my thumb, and was very difficult to pull off my foot. Do you have any idea what type of leech it may have been? I am interested in finding out more about them. I have been holidaying in the area for 20 years and have never seen leech like that before.

Margaret said...

Hi Trent,

My knowledge of leeches is pretty limited, but I wonder if the leech you've found is a Tiger Leech Haemadipsa picta? See this image, for example:

So far, I've only been able to find references to them in Borneo, but maybe they're in Australia too.

Maybe you could drop a line to the Australian Museum in Sydney. They're great at IDs. You can contact them at:

Good luck, and if you get an ID, please let me know!