Mites & Ticks (Arachnida: Acari)
Mites, including ticks, are traditionally grouped in a taxon called Acari. With more than 54,000 known species and an 10-20x this yet to be described, mites are the most diverse group of arachnids (Beaulieu et al. 2019). Their fossil history goes back to at least the early Devonian period. Acarologists (people who study the Acari) have proposed a complex, and frequently changing, set of taxonomic ranks to classify mites (Beaulieu et al. 2011; Schatz et al. 2011; Walter et al. 2011; Zhang et al. 2011). In most modern treatments, the Acari are considered a subclass of the Arachnida and are composed of two superorders or orders: Acariformes (or Actinotrichida) and Parasitiformes (or Anactinotrichida), The monophyly of the Acari is open to debate (Lozano-Fernandez et al. 2019), and the relationships of the acarines to other arachnids is not at all clear. In older treatments, the subgroups of the Acarina were placed at order rank, but as their own subdivisions have become better understood, treating them at the superorder rank is more usual.
Most acarines are minute to small (for example, 0.08–1.00 mm or 0.003–0.039 in), but the largest (some ticks and red velvet mites) may reach lengths of 10–20 mm (0.4–0.8 in) (Proctor & Walter 2018). Their small size has allowed them to occupy niches and exploit resources not available to larger-bodied organisms, including living on or in the bodies of other animals as well as occupying tiny nooks on plants and fungal fruiting bodies. They are of great medical and veterinary importance, especially ticks (Parasitiformes: Ixodida), which not only damage the host by removing blood and causing irritation, but transfer viruses and bacteria that can cause disease in humans, livestock and wildlife (e.g. :, causative agent of Lyme Disease). Many mites are important agricultural pests, including many species of spider mite (Acariformes: Tetranychidae); conversely, other mites can be employed as biological control agents of pest mites (e.g., Parasitiformes: Phytoseiidae). Although mites with medical and economic importance receive the most attention, there are thousands of species that are free-living inhabitants of soil and water on all continents (including Antarctica) and ranging from the tops of the highest mountains to the abyssal depths of the ocean (Walter & Proctor 2013).
Identification, overview of biology and morphology:
- Krantz GW, Walter DE (2009) A Manual of Acarology (third edition). Texas Tech University Press, 816 pp. (link)
Ecology, evolution and behaviour:
- Walter DE, Proctor HC (1999) Mites: Ecology, evolution and behaviour. Univ. NSW Press, Sydney and CABI, Wallingford: 322 pp (link)
Beaulieu F, Knee W, Nowell V, Schwarzfeld M, Lindo Z, Behan‑Pelletier VM, Lumley L, Young MR, Smith I, Proctor HC, Mironov SV, Galloway TD, Walter DE, Lindquist EE (2019) Acari of Canada. In: Langor DW, Sheffield CS (Eds) The Biota of Canada – A Biodiversity Assessment. Part 1: The Terrestrial Arthropods. ZooKeys 819: 77-168. https://doi.org/10.3897/zookeys.819.28307
Beaulieu F, Dowling APG, Klompen H, de Moraes GJ, Walter DE (2011) Superorder Parasitiformes Reuter, 1909. In: Zhang, ZQ. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness. Zootaxa3148: 123–128 (pdf)
Lozano-Fernandez J, Tanner AR, Giacomelli M et al. (2019) Increasing species sampling in chelicerate genomic-scale datasets provides support for monophyly of Acari and Arachnida. Nat Commun10:2295 https://doi.org/10.1038/s41467-019-10244-7
Proctor HC, Walter DE (2019) The causes & consequences of being small: an exploration of what it means to be a mite in four acts. International Journal of Acarology44:8, 347-348, DOI: 10.1080/01647954.2018.1577528
Schatz H, Behan-Pelletier VM, Barry M. OConnor BM, Norton RA (2011) Suborder Oribatida van der Hammen, 1968. In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness. Zootaxa3148: 141–148 (pdf)
Walter DE, Bolton, Bolton S, Uusitalo M, Zhan ZQ (2011) Suborder Endeostigmata Reuter, 1909. In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness. Zootaxa3148: 139–140 (pdf)
Walter DE, Procter HC (1999) Mites: Ecology, evolution and behaviour. Univ. NSW Press, Sydney and CABI, Wallingford: 322 pp (link)
Zhang ZQ, Fan QH, Pesic V, Smit H, Bochkov AV, Khaustov AA, Baker A, Wohltmann A, Wen T, Amrine JW, Beron P, Lin J, Gabrys G, Husband R (2011) Order Trombidiformes Reuter, 1909. In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness. Zootaxa3148: 129–138 (pdf)
Photos by Marshal Hedin, Bryan Reynolds and Joe Warfel