Mites and Ladders

Koalachirus perkinsi (Domrow) - the koala fur mite

Most mammals have mites that live in their fur and that don’t usually seem to do them much harm.  People don’t have these mites, probably because we don’t have much fur, but other primates do.  These ectosymbionts are highly specific to their particular hosts and are modified in various ways to cling to their hosts hairs.  They slide up and down the hair to access their food (which mostly seems to be oils and other fatty materials) and probably to regulate their temperature.

 

In the case of the koala fur mite, Koalachirus perkinsi (Domrow), the first two pairs of legs and their bases tightly clasp a hair of the host (you can see a ventral view of the mite with the groove that receives the hair here).  This particular mite came from a sickly koala at a rehabilitation centre.  Too ill to spend much time grooming (which usually keeps the population in check), the koala was literally crawling with mites and I was brought a large vial of them to identify.

 

Much to my surprise, when I opened the vial a horde of mites scrambled out and dashed helter-skelter across my desk.  Although the front legs look inappropriate for mad dashing, they have slender pretarsi that are folded out of the way when riding the hair.  When unfolded they are capable of surprising bursts of speed, which I suppose helps them get from one koala to another.

A menagerie of microarthropods

A selection of mites, springtails, and a Parajapyx

I got interested in mites through soil ecology and I’ve yet to lose my amazement that one can find dozens of species of microarthropods living in a few handfuls of decomposing plant matter almost anywhere.  True desert soils usually only have a couple dozen, and there are probably only 5-6 dozen species of microarthropods known from the Antarctic continent, but pretty much everywhere else a handful or two of litter may have a dozen dozen or more.  A couple of years ago a friend who was writing an ecology text asked me for a plate showing diversity in the decomposers, and I made him this.  These mites (mostly), springtails (2), and a more or less insect are all scaled the same and you might be able to faintly make out the 0.1mm scale bar in the middle of the picture.

A mite with a mite problem

5 hypopi hitching a ride on an Athiasiella

This morning Myrmecos Blog, the place to go for spectacular ant pictures, links to a picture on Flickr by Brian Valentine of a couple of red ants from a compost heap covered with mites. I especially like the ones sticking to the foreground ant’s eye. These look like the dispersal stage of another Astigmatina, possibly a species of the acarid genus Sancassania, as they are common in decomposing material, but then so are several other families. If the compost is very wet and stinky, then they may be Histiostomatidae. The dispersal stages are technically called ‘heteromorphic deutonymphs’, but an older term ‘hypopus’ (plural – hypopi) is easier on the tongue. Hypopi are bizarre for a number of reasons. For example, most have some of their posterior ventral setae modified into a sucker plate that allows them to latch onto surfaces such as insect cuticle – or that of larger mites for that matter. Actually anthing with an appropriate surface that wanders through a compost heap can become covered with [these] little hitchhikers – the famous Australian medical acarologist, Bob Domorow, once published a picture in Acarologia of a skink absolutely encased in [hypopi] CORRECTION – deutonymphs, yes, but of a uropodid mite, not astigmatine hypopi.  See Domrow, R. 1981. A small lizard stifled by phoretic deutonymphal mites (Uropodina). Acarologia 22:247–52

Hypopus underside – note tiny ‘head’ and sucker plate (bottom)

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A jumping mite with no males

It hops, but it doesn't fool around

Species that are represented only by females are very common in the Acari. This isn’t supposed to be. For example, you may have heard about Muller’s ratchet, an accumulation of unrepaired mutations in asexual (and hence assumed ameiotic) organisms that is supposed to make asexual reproduction a one-way street to deleterious DNA. Meiosis is a good way to repair genetic mutations, but not the only one, and meiosis does not have to result in genetic recombination.

You may have heard about the Red Queen Hypothesis, probably the most vivid model to explain the maintenance of sex in terms of staying ahead of your parasites and competitors:
“Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!” (The Red Queen in Lewis Carroll’s Through the Looking Glass)

Well, maybe, but there are an awful lot of mites that have done away with their males and seem to be plodding along just fine. Many of these parthenogens are in early derivative lineages and seem to have been around for a very long time, such as this Terpnacarus globosus. I reared this species for many generations of mother to daughter to granddaughter and so on with never a sign of a male. Also, more to my surprise, I found out they jump! Perhaps that is how they have solved the Red Queen conundrum.

Evimirus attack

Eviphididae from Mars

Perhaps only an acarologist would find this image strange, but the curlicues coming out of the peritrematal shields of this Australian species of Evimirus (Mesostigmata, Eviphididae) shouldn’t be there. Well, not unless they drown in alcohol. The large pore on the peritrematal shield apparently has a defensive function and squirts out something that hardens in ethanol. Didn’t do this mite much good, but allowed me a rare flight of fancy.

House Dust Mite

A house dust and flour mite - Dermatophagoides farinae

Although the world is filled with spectacular and mostly beneficial or harmless mites, most of the image requests that I get are for those relatively few species that cause us harm.  Here’s one that sort of causes us harm, one of the inhabitants of our house dust Dermatophagoides farinae Hughes.  Unlike what you might think from its generic name, Dermatophagoides don’t really eat our skin, but more like munch on the microbes that grow on the skin flakes we castoff with abandon wherever we go.  The species name, farinae (Latin for ‘of flour’), however, is indicative of where else you might find this mite.  This particular specimen came out of a packet of cake mix along with a few million compatriots and caused an unfortunately allergic baker to go into anaphylactic shock.  Although this mite is harmless itself, it’s skin and faeces are highly allergenic to some.

As I mentioned before, I find white the most difficult colour to manage.  In life, the body of this mite is a translucent whitish colour that I have never been able to successfully reproduce.

 

Box Mites

 

Phthiracarid mite - lateral

The evolutionary history of oribatid mites (aka beetle, moss, and armoured mites) must have been too full of adventure, because these are now the most unadventurous of mites.  Adults are slow-moving, deliberate, and heavily encumbered in armour.  Although their subordinal name, Oribatida (aka Oribatei, Cryptostigmata), may be derived from the Greek for ‘mountain’ (ori) and ‘one who roams’ (bat), it is hard to imagine oribatids lumbering uphill for any great distance (which begs the question as to how they came to be found in soil almost everywhere, including mountain tops and rainforest canopies).  Without a doubt, though, defence against predation is one of the dominant themes in the history of the Oribatida.

 

Ptychoidy in Mesoplophora

 One remarkable type of defence that has evolved at least three times in the Oribatida is called ptychoidy (more Greek, ‘ptych’, a fold).  Ptychoid mites are able to fold their legs into their bodies and close the anterior shell-like aspis over the legs, giving rise to a less English-tongue-twisting name, ‘box mites’.

 

 

A phthiracarid box mite - ventral view

Box mite seems an especially appropriate name for the members of the family Phthiracaridae that have large rectangular plates covering the genital and anal openings that rather resemble the leaves of a box.  For those of you wondering, yes that is the same ‘phthir’ as the Greek for louse – why ‘louse mites’ I have no idea, and why a somewhat related family are called ‘good lice mites’, Euphthiracaridae, is equally mysterious to me.

Sometimes ptychoidy doesn’t seem to be enough protection.  Here are couple of versions of an SEM (derived from single digital grab) of an Australian phthiracarid box mite that also encases itself with a layer of soil.  Presumably this serves as a visual or, more likely, tactile camouflage that increases the chance a predator will move on (‘get along now, nothing but a bit of dirt, your dinner is elsewhere’).

 

A dirty grayscale box mite

Above is a grayscale image that has been mostly masked from the low contrast or messy background of the original SEM.  The arrows point to a few areas in between the setae, claws, and legs where I had yet to clean out the background.  Masking around the setae is the most tedious part of creating these images.  The image below has been false coloured to show the sclerotized body as a reddish brown seen through the dirty tan of the soil layer, the legs a lighter colour, and the soft cuticle at the base of the legs (soft cuticle there is necessary for the mite to be able to withdraw its legs into the body) a sort of fleshy colour.  In life, this soft cuticle was a semitranslucent white, but I find white the most difficult colour to recreate without losing all detail.

A spruced-up version of a dirty box mite

 

Xanthodasythyreus toohey Walter & Gerson

Xanthodasythyreus toohey Walter & Gerson

Xanthodasythyreus toohey Walter & Gerson is a slow-moving mite hiding in a pincushion of 39 long, barbed setae.  It lives in dry surface soil such as the litter at the base of grass trees (Xanthorrhoea spp.) in the open forests of eastern Australia.

 

In order to capture as much of the mite in focus as possible, 18 separate digital scanning electron micrographs (SEMs) of about 1 mb each were needed.  Each image was made semi-transparent, then overlaid as a separate layer, then restored to full opacity in an image processing program.  The new composite image was then ‘masked’, that is isolated from the background and a new background was created.  Since SEMs are Grayscale, and mites are not, I then tried to recreate the colours of the mite as it was when it was alive.  In all, this image took about 40 hours of intense and concentrated work to produce.  That’s a lot of time in the evening and on weekends to spend on a single mite image, but this one has proven highly popular featuring, e.g. as a full page spread in Popular Science (A mite in a million.  Popular Science, October 2001, p. 44), on the cover of the just released A Manual of Acarology 3rd Edition (Texas Tech University Press), and so I am told, in Maxim under the title ‘A really bad hair day’.

 

Xanthodasythyreus is not found in North America, but another member of the family (Dasythyreidae), Dasythyreus sp. has been found on logs in boreal forest at George Lake in Alberta, Canada.  This may be the same species as Dasythyreus hirsutus Atyeo which bears 179 whiplike setae on its back and was described from tree bark in Arkansas, USA.  Fortunately, I do not have any SEMs of Dasythyreus, because I am sure that trying to layer and mask 179 pairs of dorsal setae (let alone those on the legs) would be a really bad hair month.  Dasythyreus species are known to be phoretic (i.e. hitch rides) on click beetles (aka elater beetles, Coleoptera: Elateridae).

The Return of the Mite Image Gallery

This blog will be devoted to mites and mite art. My original Mite Image Gallery was hosted by the University of Queensland until I left there in 2003. Since then it has been lying dormant on a variety of computers in a much colder land. Many of my images continue to be available on the web (e.g. in interactive keys) and, if you are fortunate enough to live in Australia, you may have seen some of them at the recent Ornamentamology exhibit created by the Jewellers and Metalsmiths Group Queensland, but amazingly, there doesn’t seem to be a site devoted to appreciating the often bizarre beauty of the Acari. Now there is.

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