Ticks, ‘scrub itch’ and the illnesses that go with them are known hazards of life in North Queensland, especially for people who spend time in the bush as farmers or bushwalkers. I have wanted to write about them for years but the subject is complicated and I have only recently found time to sort it all out to my own satisfaction.
Here we go, then – but first a disclaimer: my information is the best I can offer but I’m not a health professional. If you’re sick and suspect ticks or mites, please see a doctor. Tell them where you have been, too, as it will probably help their diagnosis.
Ticks and mites are arachnids. They are not insects but related to spiders.
All of them need a blood meal at some stage of their life cycle, and many of them will take human blood instead of their usual fare (i.e., the blood of marsupials, rats, cattle, dogs, etc).
Some of their bites provoke an allergic reaction.
Some of them inject poisons (toxins) in their saliva as they feed.
Some of them inject bacteria (Rickettsia family or others) which can make us very sick with typhus or other diseases. Antibiotics normally clear up these illnesses quite well, if we act quickly enough.
Ticks should be removed as quickly as possible when discovered but (importantly) without squeezing their bodies.
Most people seeing the small creature above (body length about 5mm) would say immediately that it’s a spider. Most of the rest would count the legs – yes, eight not six – and then say it’s a spider. Most of the rest of the rest would think it’s a spider and say “Eeek!” even though it’s so small. And then there’s the tiny minority who would say, “That’s interesting. I think that’s a Harvestman.” These last few would be right, too.
Mike Downes brought this one to me after saying just that, and patiently held its home rock while I took my photos. This happened on the Wildlife Queensland walk along the Dalrymple Track, up near Broadwater, last Sunday. There will be is more about that walk here and on the WQ blogin due course – but what are Harvestmen, and why aren’t they spiders?
Spiders are the best known group of a larger category of invertebrates called Arachnids, all of which have eight legs. The other arachnids include scorpions, ticks, mites and several quite obscure and unfamiliar groups; Wikipedia sets out the characteristics and relationships on this page, but the important thing for now is that Harvestmen are as distinct from spiders (evolutionarily) as scorpions, however much they look like spiders. Technically, Scorpiones (Scorpions), Opiliones (Harvestmen), Acari (Mites and Ticks) and Araneae (Spiders) are Orders within the Class Arachnida.
As Wikipedia says, “The most obvious difference between harvestmen and spiders is that in harvestmen the connection between the cephalothorax and abdomen is broad, so that the body appears to be a single oval structure.” Their legs are also longer than those of most spiders, though not usually as long as our Daddy Long-legs, but other differences are not reliably visible to the naked eye. Speaking of eyes, Harvestmen have only two whereas most spiders have eight.
CSIRO’s invertebrate site is usually good for information about Australian creatures but its page on Opiliones doesn’t have much to say except, “Harvestmen are most commonly found throughout the damper regions of Australia although some species have adapted to life in the more arid regions of the country. Most live in moist leaf litter but can also be found living under rocks and logs or under the bark of trees.”
Arachne.org has one page on Opiliones, with some good photos, amongst its “Other Arachnids”.
The only other resource I can recommend, Wikipedia’s Opiliones page which I quoted earlier, is not about Australian Harvestmen in particular but has plenty of good information about the whole order.
[Updated 8.11.15 to add links to associated reports.]