Box Mites


Phthiracarid mite - lateral

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

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

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

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

A spruced-up version of a dirty box mite



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4 Responses to “Box Mites”

  1. Macromite’s Blog: scanning electron micrograph perfection | Archetype Says:

    […] each of those hairs on the legs and the feather-like hairs on the body to produce the image above (from this post). Notice how the true cuticle of the mite’s body peeks at varous points in salmon color […]

  2. Dave General Says:

    It might interest you to know that Myrmecina ants are specialized predators of oribatid mites (Masuko 1994). The workers tear the mite open like a watermelon and the larvae stick their specialized heads into the mite to feed.
    Another great post.

    • macromite Says:

      Hi Dave,

      Yes the Myrmecina opening canned oribatid mites and feeding them to their larvae sound cool. Adelomyrmex larvae have similar elongate heads and may also be fed canned mites. I haven’t seen any of these, but one of my students and I did a study on scydmaenid beetles – they grasp the armoured mites in their front tarsi, spin them around like a basketball and snip off their legs, and then go in through one of the weak spots on the venter (genital or anal openings, mouth).



  3. Out of the box: A can of lice, good lice, naked middle thirds, and the hideous truth « Macromite's Blog Says:

    […] this problem in other posts, but it hasn’t gone away, so here’s a current example: Box Mites. Being a ‘box mite’ is more a grade of evolution than a taxon – the ability to […]

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