This "little superman" among animals can actually stack physical and chemical buffs when facing enemies

In nature, all kinds of animals have evolved different forms to survive. Large animals rely on thick fur to resist damage. But for small animals to defend themselves, it is not enough to just stack "shields". They must evolve unexpected defense methods. For example, some animals rely on mimicry to blend themselves with the outside world, making it difficult for natural enemies to detect; some animals rely on chemical defense, that is, releasing toxic chemicals to resist foreign enemies.

Tigers and brown bears are both top predators, and their thick fur provides them with top-level defense (Image source: Pixabay)

The moth wax cicada clings to the bark. In order to better simulate the mottled lichens, the colors on their wings are also different. There are five moth wax cicadas in the picture. Can you find them? (Photo source: Veer Gallery)

In an emergency, ground beetles fire a series of "chemical shells" from their anus to repel enemies (Image source: Veer Gallery)

But among these creatures, there is an insect called oribatid mites that can be said to be the "little superman" of the animal kingdom. Studies have shown that oribatid mites secrete substances called holocrons, which are homologous to the venom of spiders and scorpions and can cause respiratory paralysis in mice.

But if it is just chemical defense, the oribatid mite is not enough to be called the "little superman" among animals. What the oribatid mite really relies on is its strong physical defense ability. The shell of the oribatid mite is formed by the mineralization of calcium salts (such as calcium carbonate, hydrated calcium oxalate and calcium phosphate, etc.), which makes the shell of the oribatid mite extremely hard. In addition, the oribatid mite has wing-shaped epidermis and upright bristles to protect its legs. These make the oribatid mite have the survival ability that can be called "little superman".

In an experiment on the load-bearing capacity of oribatid mites, a mite weighing about 420ug was able to bear a weight of 110.17g (Image source: Sebastian Schmelzle and Nico Blüthgen)

Why do oribatid mites have such strong defensive capabilities? This has to do with the pressure that predators bring to oribatid mites.

Oribatid mites belong to the phylum Arthropoda, class Arachnida, subclass Acari, order Sarcoptes, and suborder Orimites. They are a type of small arthropod with a large number of species, a wide distribution, a variety of diets, and diverse living habits and living environments. Oribatid mites are tiny, with a body length generally ranging from 300 to 700 microns. The body wall of oribatid mites is ossified and mineralized to varying degrees, and they resemble beetles, hence the name.

The morphology of Acrotritia sinensis Jacot, 1923 under an optical microscope (Photo credit: Liu Dong)

Oribatid mites mainly live in the soil, especially within about 5 cm of the soil surface. There are many predators in the soil, such as spiders, pseudoscorpions, ants, etc. These predators feed on soil animals, especially the large number of oribatid mites. Take pseudoscorpions as an example. Pseudoscorpions can grab oribatid mites with the claws of their entire limbs and kill them by squeezing them with their chelicerae, or pseudoscorpions can put oribatid mites in their mouthparts and kill them with toxins. Faced with these predators, oribatid mites have to evolve stronger physical defense capabilities in order to survive.

Pseudoscorpion (Photo source: Veer Gallery)

From a certain angle, it's pretty cute↓

Oribatid mites living in the soil (Image source: Pixabay)

Why did I think of "mites"?

Since the word "mite" is also found in the word "oribaridin", we may involuntarily think of the disgusting "mites".

Mites are one of the common pests in our lives. Their excrement and secretions are allergens that can easily cause allergic reactions in people. They can cause allergic dermatitis, asthma, bronchitis, nephritis, allergic rhinitis and other diseases, causing inconvenience to human work and life and seriously endangering physical health.

For more information about mites, please go here → Mites: Don’t try to get rid of me, I will become one with you

However, although oribatid mites are also members of the mite family, they mainly live in the soil and are a type of free-living mites. They are not harmful to humans and are even beneficial insects in some ways.

Ecological functions of oribatid mites

Oribatid mites play an important role as decomposers in the material cycle of soil ecosystems. Oribatid mites directly participate in the decomposition process of litter in the soil by crushing and feeding. During this period, the activities of oribatid mites also indirectly affect the decomposition of litter by changing the physical, chemical and biological community properties around them. The decomposed litter is easy to infiltrate and leach, and the contact area with other soil organisms is greatly increased, which accelerates the circulation of nutrients.

Oribatid mites decomposing litter (Image source: Pexels)

Oribatid mites also crush litter, plant roots and stems, animal feces and carcasses in the soil through feeding activities, and then release the nutrients in them through further decomposition by microorganisms, and mix them with the soil to form fertile humus. Whether it is feeding activities or daily activities, the movement of oribatid mites will inevitably lead to the movement of soil particles and changes in the overall appearance and structure of the soil, which plays an important role in maintaining good soil aggregate structure, porosity, air permeability, water permeability, water content and other physical properties. In addition, the secretions of oribatid mites themselves and the substances released by decomposition are also important for improving soil fertility (such as the content of elements such as C, N, Ca, etc.) and regulating soil chemical properties such as pH value.

Among mites, there are dust mites and scabies mites that are harmful to human health, as well as oribatid mites that protect the earth's skin and soil. We should actively prevent and control harmful mites. As for oribatid mites, we should try our best to protect them so that they can better play the role of soil guardians.

Protecting our common home (Photo source: Pexels)

References:

[1] Liu Dong. 2021. Biodiversity Mycota, Flora, Fauna, Oribatidae, Jilin Province. Changchun: Jilin Education Press, 514 pages.

[2] Liu Dong, Chen Jun. 2023. A review of 100 years of research on oribatid mites in China. Acta Arachnidis Sinica, 32(2): 69-73.

[3] Ye Xiangguang et al. 2023. Domestic Mites in China. Hefei: University of Science and Technology of China Press, 486 pages.

[4]Balamonica, K., Saravanan, TJ, Priya, CB, & Gopalakrishnan, N. (2019). Small creatures can lift more than their own bodyweight and a human cannot-an explanation through structural mechanics.

[5]Galtier, N., Heimburger, B., & Jaron, KS 2021 Haplotype divergence supports long-term asexuality in the oribatid mite Oppiella nova. Alexander Brandt, Patrick Tran Van, Christian Bluhm, et al. Proceedings of the National Academy of Sciences of the United States of America, 118(38): e2101485118.

[6]Labandeira, CC, TL Phillips & RA Norton. 1997. Oribatid mites and the decomposition of plant tissues in paleozeoic coal-swamp forests. Palaios, 12(4): 319-353.

[7]Norton, RA & Behan-Pelletier, VM 2009. Oribatida. In: Krantz, GW & Walter, DE (Eds.), A Manual of Acarology. Third Edition. Lubbock: Texas Tech University Press, pp. 430-564.

[8]Rosenberg, Y., Bar-On, YM, Fromm, A., Ostikar, M., Shoshany, A., Giz, O. & Milo, R. 2023. The global biomass and number of terrestrial arthropods. Science Advance, 9: eabq4049.

[9]Schatz, H.. 2002. The Oribatida literature and the described oribatid species (Acari) (1758-2001) – an analysis. Abh. Ber., 74(1): 37-45.

[10]Schmelzle, S., & Blüthgen, N. (2019). Under pressure: force resistance measurements in box mites (Actinotrichida, Oribatida). Frontiers in zoology, 16, 24.

[11]Shear, WA, Bonamo, PM, Grieson, JD, Ian Rolfe, WD, Smith, EL & Norton, RA 1984. Early land animals on North America: evidence from Devonian Age arthropods from Gilboa, New York. Science, 224: 492-494.

Author: Chang Liang1 Li Chunbo1,2 Liu Dong1 Wu Donghui1

Author Affiliation:

1. Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences

2. Shenyang Normal University

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