Mites (Acari or Acarina) are themost diverse and abundant of all arachnids, but because of their small size(usually less than a millimeter in length) we rarely see them. Theticks are an exception, in that they are usually bigenough to see, especially when they are filled with blood. Red velvetmites are also among the giants of the Acari (to 10 mm), and can often beseen hunting on the ground or on tree trunks. Water mites are rarely morethan a few millimeters long, but their bright colours and rapid movementoften bring them to our attention. At the smaller end of the mite sizerange are species like the human follicle mite or the honeybee trachealmite - small enough to raise a family within a human hair follicle orwithin a bee's respiratory tube, and too small (ca. 0.1 mm) to see withouta microscope.

Mites are also among the oldest of all terrestrial animals, with fossilsknown from the early Devonian, nearly 400 million years ago (Norton et al.1988, Kethley et al. 1989). Three major lineages are currently recognised:Opilioacariformes, Acariformes andParasitiformes (Krantz 1978, Johnston 1982, Evans 1992).About 45,000 species of mites have been described - a small fraction(perhaps 5%) of the number of species estimated to be alive today.

Mites are truly ubiquitous. They have successfully colonized nearly everyknown terrestrial, marine, and fresh water habitat including polar andalpine extremes, tropical lowlands and desert barrens, surface and mineralsoils to depths of 10 meters, cold and thermal surface springs andsubterranean waters with temperatures as high as 50C, all types ofstreams, ponds and lakes, and sea waters of continental shelves and deepsea trenches to depths of 5000 meters. Some idea of mite abundance anddiversity can be gained from analysis of one square meter of mixedtemperate hardwood or boreal coniferous litter, which may harbour upwardsfrom one million mites representing 200 species in at least 50 families.Within this complex matrix of decomposing plant matter, mites help toregulate microbial processes directly by feeding on detritus and microbes,and indirectly by predation on other microfauna.

Many mites have complex symbiotic associations with the larger organisms onwhich they live. Plants, including crops and the canopies of tropicalrainforests, are inhabited by myriads of mite species feeding on mosses,ferns, leaves, stems, flowers, fruit, lichens, microbes, other arthropodsand each other. Many mites found on agricultural crops are major economicpests (e.g. spider mites) or useful biocontrol agents (e.g. phytoseiidmites) of those pests. Mammals and birds are hosts to innumerable speciesof parasitic mites (e.g. scabies and mange mites), as are many reptiles andsome amphibians. Insects, especially those that build nests, live insemipermanent habitats like decaying wood, or use more ephemeral habitatslike bracket fungi and dung, are hosts to a cornucopia of mite commensals,parasites and mutualists. None of these mites exceed a centimeter inlength, and the vast majority grow to less than a millimeter, yet theyoften have a major impact on their hosts.

The Acari can be defined by the following characteristics:

• Hexapod prelarva (lost in Parasitiformes and many derived Acariformes)
• Hexapod larval stage
• Three octopod nymphal stages (variously abbreviated in derived taxa)
• Gnathosoma delimited by a circumcapitular suture
• Palpcoxal endites fused medially forming a hypostome
• Hypostome with rutella or corniculi (lost in many derived Acariformes)
• Loss of external evidence of opisthosomal segmentation, i.e. withouttergites or sternites
• Ingestion of particulate food (lost in many derived taxa)

Mites are everywhere. Mites live on every continent (including Antarctica!) and in every ocean. Scientists know less about mites than about most other animals; they don't even have a very good guess how many species of mites there are. So far there are 40,000 species of mites known to science, and there are probably 500,000 to a million more species in the world, still unknown.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); antarctica (Native ); oceanic islands (Native ); arctic ocean (Native ); indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )

Other Geographic Terms: island endemic

This is a very big group of very diverse and very small species of arachnids. The biggest are the ticks, some of them can be over 2.5 cm long. They are giants compared to most mites. Ticks are actually just one group of mites, so we will use "mites" to refer to mites and ticks both. Most mites are less than 1 mm long, and some other mites are the smallest arachnids, they grow to less than 0.2 mm.

Like all arachnids, most mites have eight legs (but see "How Do They Grow"). On the front of the body they have two sets of mouthparts. The outside set are called palps, and they are similar to the pedipalps in spiders, They look like tiny short legs, and are used for sensing things and grabbing prey. Between the palps are the mouthparts, called "chelicerae" (kel-iss-er-ee). Different groups of mites have different kinds of mouthparts: some are sharp tubes for stabbing and sucking, some are pincers for grabbing and cutting, some are like combs for filtering little particles of food.

Some mites have eyes, but many are blind. They all have bristles and hairs on their bodies that they use to sense their environment.

Unlike spiders and most other arachnids, the bodies of mites and ticks are not divided into sections. The only other group of arachnids with bodies like this are the harvestmen, but they are much larger and have much longer legs.

Most mites are brown, but some groups are partly red or yellow, and some water mites are blue, green, or even purple.

Range length: 0.2 to 25.0 mm.

Other Physical Features: bilateral symmetry ; polymorphic

Sexual Dimorphism: female larger; sexes shaped differently

The ancestors of mites lived in soil and dead leaves, and that's where the most diversity of mites is, but mites have evolved and adapted to almost every habitat on Earth. They live everywhere on land: from hot deserts to cold caves, from rainforest to arctic tundra. They are found in every kind of freshwater.

In the ocean they are all over the bottom, on coral reefs, mud flats, and in deep trenches. About the only place they don't live in the ocean is swimming in open water.

Many mite species are parasites, and live on or inside other organisms.

Habitat Regions: temperate ; tropical ; polar ; terrestrial ; saltwater or marine ; freshwater

Terrestrial Biomes: tundra ; taiga ; desert or dune ; chaparral ; forest ; rainforest ; scrub forest ; mountains

Aquatic Biomes: benthic ; reef ; oceanic vent ; lakes and ponds; rivers and streams; coastal

Wetlands: marsh ; swamp ; bog

Mites eat many different kinds of foods. Some species suck juice from plants, some eat fungi, some eat other small animals. Some are filter-feeders, feeding on protists and other cells growing in liquid. A few species are parasites, feeding on the bodies or blood of larger animals. Every group of animal has mite parasites except fish.

Many soil mites help break down dead plant material and improve the soil. Some parasitic mites carry diseases that have strong effects on their hosts. Many mite species live in the nests of other animals.

Ecosystem Impact: biodegradation

Species Used as Host:

• Different mites species are parasites of every kind of animal except fish.

Mutualist Species:

• Social insects (ants, termites, wasps, bees)

Commensal/Parasitic Species:

• Social insects (ants, termites, wasps, bees)
• Bird nests
• Mammal nests

Most mites hide when they can. Some species have very hard exoskeletons to protect them. Others have toxic chemicals in their bodies so they taste bad. These toxic mites are often brightly-colored to warn their predators not to bother. Some plant mites spin webs and hide under them. The webs tangle and slow down small predators.

Known Predators:

• Thysanoptera
• Formicidae
• Carabidae
• Coccinellidae
• Chrysopidae
• Opiliones
• other Acari 
• small Araneae 
• small Aves 
• small Actinopterygii 
• small Anura 
• small Anura 
• small Caudata 
• small Squamata 
• small Aves 

Acari (Acarina (mites & ticks)) is prey of:
Lagopus
Plectrophenax nivalis
Calidris maritima
Araneae
Abax
Philanthus
Soricidae
Hymenoptera
Salvelinus fontinalis
Amphisbaena caeca
Eleutherodactylus coqui
Eleutherodactylus richmondi
Eleutherodactylus portoricensis
Eleutherodactylus wightmanae
Eleutherodactylus eneidae
Mimocichla plumbea
Anolis evermanni
Anolis stratulus
Anolis gundlachi
Leptodactylus albilabris
Sphaerodactylus klauberi
Sphaerodactylus macrolepis
Typhlops rostellatus
Pseudoscorpionida
Coleoptera
Thysanoptera
Secernentia nematodes
Caracolus caracolla
Anolis gingivinus
Anolis pogus
Orthoptera
Formicidae
Diptera
Chilopoda
Pomatoschistus microps

Based on studies in:
Norway: Spitsbergen (Coastal)
England: Oxfordshire, Wytham Wood (Forest)
New Zealand (Grassland)
Puerto Rico, El Verde (Rainforest)
USA: Colorado (River)
Scotland (Estuarine)

This list may not be complete but is based on published studies.

Acari (Acarina (mites & ticks)) preys on:
dead plants

Lepus americanus
total litter
fungi
humus
Charadrius morinellus
phanerogams
lichens
Bryophyta
Collembola
Sericothrips variabilis
Thysanoptera
Aeolothrips
Eleutherodactylus coqui
Eleutherodactylus richmondi
Eleutherodactylus portoricensis
Eleutherodactylus wightmanae
Eleutherodactylus eneidae
Eleutherodactylus hedricki
Anolis evermanni
Anolis stratulus
Anolis gundlachi
detritus
POM

Based on studies in:
Norway: Spitsbergen (Coastal)
Canada: Manitoba (Forest)
England: Oxfordshire, Wytham Wood (Forest)
New Zealand (Grassland)
Tibet (Montane)
Puerto Rico, El Verde (Rainforest)
USA: Illinois (Agricultural)
Scotland (Estuarine)

This list may not be complete but is based on published studies.

Mites mainly communicate by touch and scent, and by taste when they are close to each other. Males and females mainly use scent to find each other when they are looking for mates.

Mites have very poor eyesight when they can see at all. The best most can do is tell light from dark.

Mites hatch from eggs. As they grow, they have to shed their exoskeleton all at once, this is called molting. Many mites go through metamorphosis, in which their body changes as they grow. The first active stage of a mite is called a larva, it has six legs. After its first molt, it is called a protonymph and has eight legs. It molts (and sometimes changes body shape) two more times before it becomes an adult. Not all mites do this, some species skip some stages. Other species change a lot between stages, starting out as small parasites but later becoming big fuzzy predators. Other mites have a stage that is specialized for traveling. It has big claws to grab on to a larger animal (like a beetle or an ant) and catch a ride to a new food source.

Development - Life Cycle: metamorphosis

Most mites live a year or less. Some short-lived species go from egg to adult in a couple of weeks, and usually only live a few weeks. Some slow-living soil species can live for several years.

Mating System: monogamous ; polyandrous ; polygynous

After mating, most female mites lay eggs. In some species they keep the eggs inside until the young are ready to hatch. A single female mite can lay from dozens to hundreds of eggs.

Some species of mites reproduce without mating. Each member of these species is a female, and can lay eggs that grow and hatch without being fertilized.

Key Reproductive Features: semelparous ; iteroparous ; seasonal breeding ; year-round breeding ; parthenogenic ; sexual ; fertilization (Internal ); ovoviviparous ; oviparous ; sperm-storing

In most mite species, the only parental care is when the female chooses a place to lay her eggs. Males don't help at all, and the female leaves after laying. In a few species, the mother guards her eggs, or holds them in her body for protection until they hatch.

Parental Investment: female parental care

View Acari Tree

Hypothesis by Lindquist (1984)

Traditionally, the mites have been treated as a subclass of theArachnida, and three major lineages have been recognised, though the namesused to refer to these groups have varied considerably (Krantz 1978;Johnston 1982; Evans 1992). Here we generally follow the names used inParker (1982), and consider that three superorders (sensu Evans 1992) ofAcari exist. The Opilioacariformes consists of a singleorder and family (Opilioacarida, Opilioacaridae) with about 20 knownspecies. The Acariformes contains over 300 families andover 30, 000 described species. Two major lineages are recognised, theSarcoptiformes (Oribatida and Astigmata) and Trombidiformes (Prostigmata).Additionally, eight families of very early derivative acariform mites arelumped into the Endeostigmata, usually considered a suborder of theProstigmata, but clearly containing taxa that belong to both majoracariform lineages. The Parasitiformes consists of threeorders: Ixodida, Holothyrida, and Mesostigmata. The Mesostigmata containsin excess of 65 families and 10,000 described species, the other twoparasitiform orders each comprise three families. About 850 species ofticks are known, but only about 30 species of holothyrans have beenrecognised.

What then is a mite? Aside from being generally tiny cheliceratearthropods with hexapod larvae, a discrete gnathosoma, and a loss ofprimary segmentation, mites are difficult to characterise. Lindquist(1984) pointed out that many of the characters used to define mites werepresent in other chelicerate orders, especially in the Ricinulei. Heproposed 11 apomorphic characteristics for the Acari (Table 8, p. 40), butseveral of these character states are not present in the Parasitiformes andpresumably have been secondarily lost. It seems that mites often are mosteasily recognised by what they are not - other arachnids, rather than by adiscrete set of acarine characters.

Among acarologists, arguments about monophyly or diphyly of the Acari haveyet to be resolved, although currently the monophyleticists seem to bedominant (see Lindquist 1984, Evans 1992). The Parasitiformes andOpilioacariformes are thought to be sister groups, and in turn this taxon(the Anactinotrichida, so named because of the absence in their setae ofoptically active actinochitin) is considered the sister group of theAcariformes (also called the Actinotrichida). Outside of the acarologicalcommunity, those interested in chelicerate phylogeny have tended to assumethat the Acari were a monophyletic assemblage (e.g. Weygoldt & Paulus 1979,Shulz 1990, Weygoldt 1997).

Recently, many acarologists have concluded that mites are closely related tothe arachnid order Ricinulei (Lindquist 1984, van der Hammen 1989, Evans1992). Weygoldt & Paulus (1979) first proposed a sister group relationshipbetween the Ricinulei and the Acari, and named this taxon theAcarinomorpha. Schulz (1990) also supported thisrelationship, but like Weygoldt and Paulus, assumed that the Acari aremonophyletic. Van der Hammen (1989) considered the Acari to be diphyletic,and the Acariformes and Parasitiformes at most distantly related.According to van der Hammen, the Ricinulei and Anactinotrichida(Parasitiformes + Opilioacariformes) are sister groups and, within anotherlineage, the Actinotrichida (Acariformes) and the non-acarine Palpigradialso are sister groups. Lindquist (1984) presented four derived characterslinking the Acari and Ricinulei (his Table 9, p. 41) and concluded that,within the Acari proper, the Opilioacariformes and Parasitiformes form asister group to the Acariformes.

In our trunk page for the Acari, we follow the hypothesis of Lindquist(1984), which suggests that a monophyletic lineage includes the Ricinuleiand the Acari. This hypothesis is based on the characters presented byLindquist, and is in agreement with that of Weygoldt & Paulus (1979) andSchulz (1990), but not with that recently proposed by Dunlop (1996).

Barcode of Life Data Systems (BOLD) Stats
                                        

Specimen Records:	270	Public Records:	12
Specimens with Sequences:	19	Public Species:	0
Specimens with Barcodes:	14	Public BINs:	6
Species:	0
Species With Barcodes:	0

Access Published & Released Data: Download FASTA File

Collection Sites: world map showing specimen collection locations for Acari

No mite species are known to be endangered, but we don't know very much about most of them, and very few people pay much attention to them. Some mite species live on larger species that are endangered, and if the larger host species is endangered, then the mites species probably is too.

Some mite species are obnoxious parasites of people and animals, and some carry diseases that they give to their host when they bite. Some plant mites are major pests of farmer's crops, and a few species of mites are pests in stored food.

Negative Impacts: injures humans (bites or stings, carries human disease); crop pest; causes or carries domestic animal disease ; household pest

Some mite predators are important for controlling pests in agriculture (they eat plant mites and larvae of pest insects). A few herbivorous mites have been used to control weeds.

Positive Impacts: controls pest population