''Trombidium grandissimum'', commonly known as the giant red velvet mite, is a species of

mite Mites are small arachnids (eight-legged arthropods) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as eac ...

in the genus ''

Trombidium ''Trombidium'' is a genus of mite with about 30 described species. Species * '' Trombidium auroraense'' Vercammen-Grandjean, Van Driesche & Gyrisco, 1977 – New York * '' Trombidium breei'' Southcott, 1986 – Europe (host: ''Agapetes galathe ...

'' in the family

Trombidiidae Trombidiidae, also known as red velvet mites, true velvet mites, or rain bugs, are small arachnids (eight-legged arthropods) found in plant litter and are known for their bright red color. While adults are typically no more than in length, so ...

. This common mite is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to northern and central India, especially in the central plateau, and it primarily inhabits arid regions. ''T. grandissimum'' live on the ground and often hidden among soil, but is commonly seen during the rainy season or after recent rain events, and therefore (along with some other red velvet mite species) has the nickname of "rain bug".

Description

''Trombidium grandissimum'' is one of the largest species of red velvet mite, with adults typically being about long. It is bright red and has a soft cushioning skin covered with fine hairs. A study of another species, the spider mite ''

Tetranychus urticae ''Tetranychus urticae'' (common names include red spider mite and two-spotted spider mite) is a species of plant-feeding mite generally considered to be a pest. It is the most widely known member of the family Tetranychidae or spider mites. It ...

'', showed that the red color was caused by

carotene The term carotene (also carotin, from the Latin ''carota'', "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the ex ...

, which was beneficial for their hibernation. ''T. grandissimum,'' belonging to the same order as spider mites, spend an extensive period of time in hibernation under the soil. This might be the reason why they also depend on red pigmentation, by which their

haemolymph Hemolymph, or haemolymph, is a fluid, similar to the blood in invertebrates, that circulates in the inside of the arthropod's body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph ce ...

is usually coloured.

Microscopy

The mites were observed under stereo microscope for the detailed classification and analysis of different parts of their body, and structural samples were processed using

ESEM The environmental scanning electron microscope (ESEM) is a scanning electron microscope (SEM) that allows for the option of collecting electron micrographs of specimens that are wet, uncoated, or both by allowing for a gaseous environment in t ...

and FESEM. The FESEM images of the front leg

sensilla A sensillum (plural ''sensilla'') is an arthropod sensory organ protruding from the cuticle of exoskeleton, or sometimes lying within or beneath it. Sensilla appear as small hairs or pegs over an individual's body. Inside each sensillum there are ...

hairs and claws at the tip usually measured around 500μm. Stalked eyes pointed with white arrows measured around 1mm. White arrows magnified by ESEM were measured around 400μm. The red velvet skin is shown to be covered by sensitive hairs. The whole body hairs showing the branches and arrangement measured around 50μm in size.

Behavior

''Trombidium grandissimum'' appears to be diurnal and will move into light, rather than darkness, if given the choice. They feed on tiny animal prey, like insects and their eggs. In the larval stage, ''T. grandissimum'' attach themselves to insects, most commonly

crickets Crickets are orthopteran insects which are related to bush crickets and more distantly, to grasshoppers. In older literature, such as Imms,Imms AD, rev. Richards OW & Davies RG (1970) ''A General Textbook of Entomology'' 9th Ed. Methuen 886 ...

, and suck their fluids; they may occasionally even suck fluids from adults of their own species. In their natural habitat, they were found to move on a horizontal plane. They seemed to be reluctant to climb up against the gravitational force which may be due to their bulky body size and shorter legs. They can easily wriggle their bodies through small openings and thus can easily get inside the burrows of ants and other insects to feed on their eggs. Males and females of Trombidiidae mites perform encircling dances, after which they pair for mating. A dead mite was found to be surrounded by ants, suggesting that they are non-toxic to other species and their cannibalistic nature suggests the same.

Relationship with humans

''T. grandissimum'' feed on insects and other mites, including species that are regarded as

pests PESTS was an anonymous American activist group formed in 1986 to critique racism, tokenism, and exclusion in the art world. PESTS produced newsletters, posters, and other print material highlighting examples of discrimination in gallery represent ...

. In their native range in India, they are gathered in large numbers when they emerge during prolonged rains. They are made into an oil-based

traditional medicine Traditional medicine (also known as indigenous medicine or folk medicine) refers to the knowledge, skills, and practices rooted in the cultural beliefs of various societies, especially Indigenous groups, used for maintaining health and treatin ...

that is said to be useful for a wide range of things, including immunity related diseases and

paralysis Paralysis (: paralyses; also known as plegia) is a loss of Motor skill, motor function in one or more Skeletal muscle, muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory d ...

.Oudhia, P. 1999b
Traditional medicinal knowledge about red velvet mite ''Trombidium'' sp. (Acari: Trombidiidae) in Chhattisgarh.
''Insect Environment'' 5(3):113. Research is being conduced to confirm or refute whether this oil has potential for pharmaceutical use.

References

{{Taxonbar, from=Q115393319 Trombidiidae Endemic fauna of India Animals described in 1867