This large and diverse group of mites includes an interesting mixture of species that vary greatly both in terms of size and body form, as well as lifestyle and feeding habits. 

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Whilst the majority of species you'll be able to find and possibly photograph will have a body size in the region of 0.5-2mm, there are many that are smaller that will go unnoticed. But there are also a few that are certainly bigger, notably members of the Trombidioidea, collectively referred to as 'velvet mites' where some species can grow to 8-10mm, possibly more. 

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Their general appearance is very variable with the smaller forms typically having an oval or elongate, relatively plain-coloured body, whereas the larger, conspicuous species are generally more bulbous, often wide-shouldered and are usually brightly coloured. They are mostly soft-bodied, weakly sclerotised mites that, in part, are distinguished from mesostigmatans by their legs, as the two pairs at the front are separated from the rear pairs such that there's a distinct gap between pairs II and III, whereas in Mesostigmata pairs II, III and IV are all next to each other. The segments also differ, tending to be quite uniform among the Prostigmata, only narrowing slightly at the joints, and with fused coxae, compared with the more variable, tapering, freely-moving structure seen in Mesostigmata.

 

Although difficult to see, most species have a tracheal system with spiracle openings, known as stigmata, located either near the base of the mouthparts or around the front dorsal edge of the idiosoma, hence the name Prostigmata. They usually, but not always, have eyes and, as noted below, have mouthparts adapted for fluid feeding.

 

I've added some brief notes in respect of the ecology or lifestyle of certain family groups, but I deliberately haven't gone into much detail as I don't have the knowledge, or indeed the space. Most of the species featured here are regarded as soil mites as they are mainly found at ground level in the soil or litter, or under deadwood and stones, but some are arboreal occurring on trees or shrubs, in mosses and lichen or under bark. They're mainly predatory mites that feed on a variety of small arthropods, but there are also plant-feeders and a few fungivores, and even some that exist on waste and decaying organic matter. And then there are the parasitic species that are associated with a wide range of hosts from slugs and snail to various invertebrates, and some animals, and even one particular group that start life as a parasite but then change their feeding habits when they're adults. The list goes on, and similarly with the plant parasites that can cause variable amounts of damage to a wide range of host species, whether harmless leaf discolouration or gall-inducing to being serious pests of commercial crops. And, if that wasn't enough variety, there are also a large number of aquatic species as mentioned below that are not covered.

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In one way or another, their feeding habits provide nutrition derived from consuming liquid in whatever form it takes and, as such, the mouthparts are variably modified for piecing and sucking, rather than tearing or chewing. Many have the chelicerae fused into a puncturing stylophore, whilst others may have different adaptions for sap-sucking. Accordingly, it's not uncommon to see the Prostigmata referred to as 'sucking mites' thereby retaining the more generic 'predatory and parasitic mites' title for the Mesostigmata fauna.

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A final observation before starting to look at the various subgroups and families is that most of the more familiar or conspicuous species have common names, such as 'whirligig mites', 'velvet mites', 'spider mites', 'concrete mites', and so on, that can often lead to confusion. I've been careful in my use of these names and have, hopefully, made the correct references where necessary. The more usual collective names, as in 'gall mites' or 'water mites' for example, are better defined and rarely cause a problem.

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The British list includes just over 1000 recognised species that are spread across 70 families, which are rather daunting numbers for a casual observer to get to grips with but, when those families are correctly segregated and broken down, the actual number that are likely to be seen and hopefully photographed becomes far more manageable and a lot easier to understand.

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The first step is to note that there are four infraorders; Anystides which includes two primary divisions (hyporders), Anystina and Parasitengona; Eleutherengonides, which is also separated into two groups Heterostigmatina and Raphignathina; Eupoides that has no higher-level taxon divisions; and lastly Lapidostommatides, which comprises just one well-sclerotised species. We can now look at each of these subgroups to focus on the superfamilies and families that we need to consider.

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Anystides - Anystina is a small division comprising just two families, Anystidae as featured below and Hydrovolziidae; whereas Parasitengona is a large group that includes over thirty families as explained in the following superfamily writeups. However, twenty-two of these families that collectively include around 170 species are in the Hydrachnidiae 'water mites' subcohort and, consequently, can be ignored as they don't come under the category of soil mites.

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Eleutherengonides - without going into detail, I don't think that there's much interest here from a photographer's point of view. I could be wrong, but at the moment I'm only able to feature a single species from the Tetranychidae family.

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Eupodides - there are fourteen families in this hyporder that are separated into five superfamilies, four of which are covered here to some degree. The Halacaridae family includes around 70 species of 'marine mites' and, as with the Hydrachnidiae,

is excluded.

  

The number of species to consider is now considerably reduced, as are the families and although I'm only able to represent

a few at present, I'm hopeful that in time I'll be able to build on this initial collection. 

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In a similar format to that used in the other groups, I've followed the systematic (hierarchal alphabetical) listed order - see the final introductory paragraph on the Oribatida page for further information - which, for convenience, are grouped into eight sections:

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     1) Anystides > Anystina > Anystoidea > Anystidae (family)

     2) Anystides > Parasitengona > Erythraeoidea (superfamily)

     3) Anystides > Parasitengona > Trombidioidea (superfamily)

     4) Eleutherengonides > Raphignathina > Tetranychoidea (superfamily)

     5) Eupodides > Bdelloidea (superfamily)

     6) Eupodides > Eupodoidea (superfamily)

     7) Eupodides > Eryophyoidea (superfamily)

     8) Eupodides > Tydeoidea (superfamily)

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The associated notes have been compiled from numerous bits of information that I've accumulated during my research, much of which has been extracted from various scientific papers. In all respects I've been careful in making sure that it relates to species that I might be able to find locally. The references made to the number of species within each family is based on the latest information available from the Soil Biodiversity UK website and the current UK Acari Taxonomy list, to which I've kindly been granted access.

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