In a Comment under the previous post, George demanded “Give us new mites! We like mites!”. Well, okay, but I’ll give you one of the few mites that I loathe, a tick. Here’s a view of the subcapitulum of a Winter Tick, Dermacentor albipictus (Packard, 1869). Sadly, ticks are mites and real mites – members of the Parasitiformes. They also tend to be relatively large – a fully engorged female Winter Tick looks like a big, black marble and is about as big as any mite gets (~1.7 cm). This individual was pretty big, about 7 mm long, but a male and so not interested or even able to engorge.
Male hard ticks (Ixodidae) have their upper side (dorsum) covered by a large, leathery plate called a scutum. In a female, the scutum is much smaller and no hindrance to her body swelling – both stretching and growing new cuticle (without moulting – very rare in arthropods) – as she fills with blood and then eggs. Both do have pretty silvery and brown patterns, though, which makes them ornate ticks, and a square, tooth-like pattern on the posterior margin of the body called festoons. Both also have the diagnostic characters of ticks such as the retrorse teeth on the hypostome (the projection between the palps in the top picture) used to anchor the capitulum (‘little head’) in the skin of a host, slicing chelicerae, a hexapod larval stage and a cluster of pits, pockets and sensory setae on the tarsus I called Haller’s Organ.
One reason I loathe ticks (and also terrestrial leeches) is that they are so blood-thirsty and avariciously desirous of slicing into your skin and regurgitating their secretions into the wound. A tick bite is invariably painful, at least once the tick has gone, and prone to infection. The infections are often delivered by the tick itself – after mosquitoes, no other arthropod group is such a good vector of disease. The feeding by the ticks themselves can be devastating both from paralyzing salivary secretions (as with the related Rocky Mountain Wood Tick or Australian Paralysis Tick) or the general irritation and loss of blood. Moose in Alberta often are covered with tens of thousands of Winter Tick resulting in hair loss, loss of condition and death. The grey, ratty and emaciated moose are called ‘Ghost Moose’ and are a sad sight.
I think that is about all I can stand to say about ticks on a fine Saturday morning. If you would like to learn more about Winter Tick and Ghost Moose, then there is no better place than Bill Samuel’s book:
Bill Samuel. 2004. “White as a Ghost: Winter Ticks & Moose” Federation of Alberta Naturalists.
If you want to learn more about ticks, try the Manual of Acarology 3rd Edition. If you aren’t in too much of a hurry and would like to learn all kinds of interesting (and often disgusting) facts about how ticks and other mites go about their lives, then I can tell you that the 2nd Edition of Mites: Ecology, Evolution & Behaviour was submitted to the publisher at the end of April. Meanwhile, I’ll leave you with a light micrograph of the subcapitulum of a male Winter Tick. You can compare it to the coloured-SEM at the top and decide which you would prefer to visit your dreams.