ACARI | Oribatida

families

The Oribatida suborder includes an interesting and diverse assemblage of tiny, well-armoured, mostly dark-coloured mites that predominantly inhabit woodland areas where they live in the soil and leaf-litter feeding on decaying material and fungi.

Of course they're not restricted to this type of habitat as they can also be found in gardens and various other environments including wetlands, but the opportunities for finding them in woodland is far greater as a good variety of species can often

be seen on rotting deadwood, especially on the underside of small fallen branches that are laying directly on the ground.

This is certainly where I've had most success photographing them, but they don't all live at ground level and, although far more difficult to spot, some are arboreal occurring on tree trunks, lichens or amongst mosses.

Most oribatids have an overall body length in the region of 300-700µm which, even at the top end, is pushing the boundaries in respect of trying to locate and photograph them in their natural habitat. However, there are quite a few that are fortunately

a tad larger that provide slightly better and more realistic photo opportunities. Most of these are still rather small at around 700-900µm, but there are some that may be up to 1200µm or even 1500µm and, therefore a little easier to spot with the naked eye. They're still a challenge, but one of the pleasures in trying to put together a portfolio of these species, apart from the variety, is that when you do find them, they're invariably resting or moving around relatively slowly.

Cepheus sp. (size comparison with an ant's head)

Cepheidae - Cepheus sp. (an average size oribatid, which is smaller than an ant's head)

Their body is protected by a number of sclerotised plates, with the adults typically having two covering the dorsum, one at the front and one at the rear, plus a varying arrangement of smaller plates on the underside. The anterior dorsal plate is called the prodorsum and is usually connected in some manner to the ventral plates, although with the ptychoid mites that can roll themselves up into a ball, it is isolated and alternatively known as the aspis. Effectively this plate covers the front part of the mite; the gnathosoma and the leading edge of the notogaster (an area of the body called the proterosoma) and often projects forward such that the gnathosoma is hidden when viewed from above. The extended portion of the prodorsum is the rostral tectum, or simply rostrum. The larger dorsal plate, called the notogaster, protects the main part of the body (an area called the hysterosoma) and sits directly behind the anterior plate with the flexible, non-hardened zone between them, if present, known as the sejugal furrow. Some species that do not have the ability to roll up, have fixed or moveable lateral plates that help to protect their legs, called pteromorphs, which may be continuous with the body and barely visible or well-developed as in the Galumnidae family.

That's a simple, generalised description, but it helps to understand the body form, which could be; dichoid where the sejugal furrow, which runs round the body between the second and third pairs of legs, is flexible allowing free movement between the proterosoma and hysterosoma; ptychoid when the ventral plates are adapted so that the legs can be withdrawn, which allows the mite to fold in its anterior dorsal plate effectively forming a protective ball that can be likened to the way a hedgehog rolls up; or holoid where the ventral surface is fused, such that articulation of the body is pretty much restricted to side to side movement.

A few other features to note are that oribatid mites do not have eyes, so to aid navigation and detecting movement, they have a pair of adapted sensory setae known as the sensillus that are shaped like feathers, clubs or simple bristles that arise from pits (bothridia) on the front of the prodorsum. Many species have a pair of conspicuous blade-like structures than run down the prodorsum called lamellae that usually end in a projecting lamellar cusp. The structure and form vary but, together with associated features such as the interlamellar setae, are important identifying characters that should be visible in photos to some degree.

Occasionally you may spot a juvenile, possibly a deutonymph although more likely an active tritonymph, but unless it's a distinctive species, such as Cepheus or one that carries exuvial scalps on its back, confirming the identity is unlikely. You might be photographing a known species or genera and a nymph comes into view, which would probably suggest it's the same species, but it's hard to be sure. Some bear a resemblance as their ontogenetic development is gradual, but there are many species, notably in the Brachypylina, that go through metamorphosis between the tritonymph and adult stages that makes association difficult even for experts. From a photographer's perspective it's not a subject that needs to be explored, but it's certainly useful to know if you've found a juvenile rather than thinking it's new species. That's exactly what happened to me when I was still learning about these species, so I thought it would be useful to include a couple of reference shots of plicate juveniles as I haven't been able to feature them elsewhere.

Cepheidae - Cepheus deutonymph

Undetermined plicate juvenile - assumed tritonymph

The latest information at the time of writing confirms that, excluding Astigmata (see below), just over 400 species of oribatid mites have been recorded in Britain. I haven't reconciled the actual number with the listing on the Soil Biodiversity website, but on the basis the data aligns, they are placed in 155 genera, separated into 67 families - a very large number of which will never be represented here.

When I first started putting this section together, I was concerned that I'd only managed to find a few species and was really struggling to get them identified. I was also mindful of the 'advice' I'd been given about trying to photograph them, but rather than admit defeat and find an easier subject, I decided to invest a lot of time and effort to gain sufficient knowledge that would allow me to do my own research rather than having to rely on outside help. I still try to get identities confirmed when I'm not sure, but unfortunately many queries go unanswered, which is why there are a few 'probably' and 'likely' qualifications in the following accounts.

In many cases I could have just confirmed the family, but I've derived a lot of pleasure from checking the associated genera and species against the latest list and then trying to see if there are sufficient visible features to confirm an identity. It's only been possible though, because Oribatid mites have been so well studied and, unlike the other groups Mesostigmata and Prostigmata, are covered by a couple of specialist books [notably the German publication "Hornmilben (Oribatida)" by Gerd Weigmann (2006), and the more recent "Oribatid Mites - Biodiversity, Taxonomy and Ecology" by Valerie Behan-Pelletier and Zoë Lindo (2023), which primarily deals with Canadian species, but is still extremely useful] and various scientific papers.

The upshot is that I'm currently able to feature various genera/species from 19 different families.

They are represented here in their systematic (hierarchal alphabetic) order which follows the formal listing used on the Soil Biodiversity UK website. I'm not sure whether it's totally up to date, but it's the best resource I have available and the only online system I've found that specifically relates to the British fauna. It's just a shame that the NHM servers that drive the database are almost constantly experiencing technical difficulties, which is extremely frustrating. However, over a period of time, I have managed to extract the required data to enable the full classification to be shown.

The accompanying text is varied dependent on the species / family and my experience; sometimes brief, but with certain species more extensive. All of the text has been written by me and, although descriptions are obviously taken from formal keys and descriptions, are my interpretations and thoughts from a photographer's perspective.

ACARIFORMES > Sarcoptiformes > Oribatida

< link to species accounts >

Either click the above < link > to read about all the various species that I've managed to photograph, or alternatively any of the following thumbnail images to jump straight to that family.

Euzetidae

Achipteriidae

Humerobitidae

Oribatellidae

Galumnidae

Oribatulidae

Phenopeiopidae

Carabodidae

Damaeidae

Peloppiidae

Camisiidae

Phthiracaridae > Phithiracarus

Cepheidae

Liacaridae > Liacarus

Hermanniellidae

Cymbaeremaeidae

Liacaridae > Xenillus

Neoliodidae

Nothridae

Phthiracaridae > Steganacarus

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Astigmata (=Astigmatina)

Although the Astigmata are placed in the Oribatida > Desmonomata infraorder where they are taxonomically ranked alongside Brachyphylina and Nothrina, they are usually treated as a separate group which is why I've included them here rather than on one of the linked pages.

Around 370 species have been recorded in Britain, but only 112 of those come under the category of 'soil mites' as the remainder are generally described as 'feather or dust mites'. They are rarely photographed due to a combination of their size and the likelihood of actually finding them and, in fact, I was originally only going to include the briefest of mentions. However, as I can now include a couple of photos, I've taken the time to do a bit more research.

They are a diverse group consisting of both free-living species that may live in soil, litter, decomposing plant matter or bird's nests for example, or parasites associated with various insects. Most species are white to pale-brown in colour, soft-bodied and poorly sclerotised, and typically with a body that is usually narrower at the front than the back, and often with long hairs.

Most chance encounters will probably be with members of the Acaridae family, which includes 50 species in 16 genera as the other families are more niche; Glycyphagidae with 24 species spread across 12 genera that mainly live in bird's nests or stored produce; Histiostomatidae which includes 20 species in 10 genera that are primarily associated with wet substrates, such as dung, mud, tree holes or decaying plant tissue; Hyadesiidae and Winterschmidtiidae collectively with 11 species of kleptoparasites; and Canestriniidae which includes 6 species which are parasites that feed on secretions of beetles.

Acaridae - likely Tyrophagus sp. (photographed on the inside of our garden waste bin)

Created July 25 | updated Aug.25 (v.2)