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Soil Mites as Decomposers: Recycling Nutrients in the Ecosystem

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The Arachnida subclass, Acari, includes all mites and ticks. The subclass is divided into two superorders, each with several orders and suborders.

Four soil mite orders or suborders represent tens of thousands of soil mite species. Oribatid mites are the most ubiquitous, followed by Mesostigmata, the predatory soil mite order. Prostigmata and Astigmata are lesser suborders.

Table of Contents

The Status of Soil Mites in the Animal Kingdom

In biology, taxonomic rank refers to the relative level (no pun intended) of a group of organisms in an ancestral hierarchy. Taxonomy allows us to recognize the basic features of fauna and flora quickly. It will enable scientists to fight over what fits where and why – each decision loaded with reputational risks and egos to match.

When it comes to mites, the argument is far from being settled. Given that they’ve only identified and grouped less than 10% of these little creatures, there’s tension around how many subgroupings there should be.

A close-up image of an orange soil mite, magnified 100 times. The mite is covered in fine, hair-like structures and appears to have four pairs of legs. The background is blurry and indistinct, with no discernible features.
Discover the Hidden Wonders of the Tiny Prostigmatid Soil Mite Magnified 100x

Knowledge of Acari systematics is still in its infancy, and adding classification beyond the established hierarchical levels is a hot topic among Acarologists.

In taxonomy, living organisms are classified and sub-group as follows

  • Domain
    • Kingdom
      • Phylum
        • Class
          • Order
            • Family
              • Genus
                • Species

Soil mites are classified as follows

  • Kingdom – Animalia
  • Phylum – Arthropoda
  • Subphylum – Chelicerata
  • Class – Arachnida
  • Subclass – Acari
    • Superorder – Parasitiformes
      • Order – Mesostigmata (predator mites)
    • Superorder – Acariformes
      • Order Sarcoptiformes
        • Suborder – Oribatei (beetle or turtle mites)
        • Suborder – Astigmata (white soil mites)
      • Order – Trombidiformes
        • Suborder – Prostigmata (a heterogeneous group of soil mites)

 Those are the four groupings of soil mites

  • Oribatei
  • Mesostigmata
  • Prostigmata
  • Astigmata

Let’s consider them individually.

Beetle Soil Mites – Oribatid Mites

A highly magnified photograph of an Oribatid beetle soil mite, showing intricate details of its segmented body, legs, and antennae. The mite appears as a small, reddish-brown creature, with multiple hairs and bristles covering its body.
Get up close and personal with the intricate details of an Oribatid beetle soil mite

The Oribatei, called beetle or turtle mites, are the most common soil mites for their shell-like bodies. They consist of about 146 families and 8,500 species. Oribatid mites don’t grow more than a four-hundredth of an inch (1 mm) long, so you may require a microscope to see their body details (shell, four pairs of legs, and claws). 

Oribatid mites are present worldwide and can be found in soil at a density of 50,000 to 500,000 individuals per square meter. In most soils, oribatid mites are known to predominate over other groups of mites and mesobiota. 

They are hardy creatures, equally comfortable at the poles and the equator, even at temperatures above 158°F/70°C. They can be found in all terrestrial environments, including the arctic and tropical zones.

Oribatid mites are a highly varied order of soil mites, with varying numbers of species found in different places based on the habitat offered. Coniferous woods have the most oribatid soil mites, followed by deciduous hardwood forests, grasslands, deserts, and tundra. 

In intensive agriculture, their numbers are lower, but extensively managed grasslands can have as many as 150 different species per square meter.

Orbatid soil mites live off fungi, algae, organic matter, dead microorganisms, and nematodes. They’re primarily scavengers and help in composting processes. Oribatid soil mites are essential to soil health. 

In composting, bacteria and fungi feed on carbon and use nitrogen-rich materials for cellular development. These microorganisms are nitrogen-rich, and when they die (usually near plant roots), that nitrogen is encapsulated in their bodies. It is only released when mesobiota, like soil mites, feed on them.

Predator Soil Mites – Mesostigmatid Mites

This is a microscopic image of a Mesostigmatid soil mite. The mite appears as a small, brownish oval shape with eight legs and several hairs or bristles protruding from its body. The background of the image is dark, and the mite is magnified to a size where its individual body parts can be seen in detail.
Get up close and personal with a Mesostigmatid soil mite an intricate world hidden in plain sight

The Mesostigmata are mostly predators feeding on other microorganisms like nematodes. A study on dwarf tomatoes to determine whether adding mesostigmatid mites can help control plant-parasitic nematodes showed a significant decline in galls.

The study shows the importance of mesostigmatid soil mites in keeping parasitic nematodes under control, a significant pest for most gardeners. The mesostigmatid soil mites are hugely beneficial in balancing soil biota populations. There are about 75 mesostigmatid soil mite families and 5,050 species.

Mesostigmatid mites are essential predators of nematodes, springtails, insect larvae, and the occasional spider mite and are often used as bioindicators. Mesostigmatid mites can relocate rapidly using phoresy, hitching a ride on beetles.

Intensive farming and the use of pesticides negatively impact soil biota diversities and, by implication, soil health.

White Soil Mites – Astigmatid Soil Mites

Zoomed in photo of two astigmatid soil mites, left has a lighter brown color, right has a darker brown color on its legs and head, and lighter brown on its body.
Side by side a light and dark astigmatid soil mite duo

Ever wondered what the tiniest white dots are in your nitrogen-rich soil? Astigmatid mites are white to tan and are soft-bodied soil mites. They are small, about six-thousandth of an inch to an eighth-hundredth of an inch (0.15 to 2.00 mm) long. 

Unlike their oribatid ancestors, mostly restricted to the soil, the Astigmatid mites can be found in other habitats. Astigmatid soil mites are the least common group. Their populations in gardening soils only increase when debris levels increase after harvesting, nitrogen applications, or rich manure applications.

Most soil-dwelling Astigmatid mites are microbe feeders. 

Red Soil Mites – Prostigmatid Soil Mites

"Up close and personal with a Prostigmatid soil mite"

Prostigamtata mites can be terrestrial or aquatic. The prostigmatid soil mites are predatory and grazers, an omnivore that boosts soil health. There are about 14,000 species grouped into 135 Prostigmatata families.

Soil Mite Families

  • Oribatidae: most extensive soil mite family
  • Eriophyidae: gall or vagrant mites
  • Tetranychidae: spider mites and clover mites
  • Tarsonemidae: cyclamen/broad mites – may be a strawberry pest
  • Phytoseiidae: Predatory mites that consume 5 to 0 pests and up to 20 pest eggs/day. They can help you control spider mites within 2-3 weeks.
  • Acaridae: bulb mites

FAQs on Are mites a Decomposer?

In Closing

These tiny creatures have huge families and are ubiquitous in almost every environment. To learn more about the different mite types and how to manage population sizes, check out the Sanitation Practices for Soil Mites post.

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