Trombidiidae

True Velvet Mites, Red Velvet Mites, Sumo Mites, Rain Bugs

Trombidiidae are among the largest , with typically 4 mm or less but some exceeding 12 mm. They display bright red coloration and a soft, velvety appearance due to dense . The exhibits complex with alternating active and inactive stages, and a dramatic shift from parasitic to predatory postlarval forms. They inhabit litter and soil surfaces across diverse geographic regions.

Allothrombium by no rights reserved, uploaded by Yann Kemper. Used under a CC0 license.

Allothrombium by no rights reserved, uploaded by Jesse Rorabaugh. Used under a CC0 license.

Allothrombium by (c) aarongunnar, some rights reserved (CC BY), uploaded by aarongunnar. Used under a CC-BY license.

Pronunciation

How to pronounce Trombidiidae: //trɒmˈbɪdi.aɪdiː//

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Distinguished from other Trombidioidea by structure visible in view. Macroscopic color differences allow preliminary field separation among syntopic : Trombidium brevimanum appears crimson red versus bright red in other species. Definitive identification requires examination of palp and often COI sequencing. are parasitic and morphologically distinct from postlarval forms, requiring rearing for species-level identification.

Images

Appearance

are conspicuously bright red to crimson, with a soft, velvety texture created by dense covering of . Most adults measure under 4 mm, but some reach 12 mm or more, making them the largest outside of engorged . The body is rounded and somewhat flattened dorsoventrally. are prominent and visible in view, important for -level identification.

Habitat

litter, upper soil layers, and soil surfaces in forests, meadows, fields, and allotment gardens. Found in mesic upland forests, uncultivated grassy areas, and lower parts of tree trunks. Activity concentrated on soil surface during early spring through late summer.

Distribution

Widespread across Europe, Asia, North Africa, and North America. Well-documented in western Palearctic including Poland, with records from Wrocław, Bieszczady Mountains, Bystrzyckie Mountains, Stołowe Mountains, Białowieża, Notecka Forest, and Vistula Spit. Distribution records from Denmark, Norway, and Sweden in GBIF.

Seasonality

Active on soil surface from early spring through late summer. One breeding cycle per year. often overwinter, becoming plump in autumn and potentially shriveling through winter energy use. laid in spring.

Diet

are of and other , creating stylostomes (feeding canals) to access liquified tissues; parasitic phase lasts 5-8 days at 22°C day/15°C night. and are active of small including economically significant pests.

Host Associations

Acyrthosiphon pisum - LARVAL_HOST; confirmed experimental for Allothrombium fuliginosum
Aphis sambuci - LARVAL_HOSTElder ; confirmed experimental for Allothrombium fuliginosum
Macrosiphum rosae - LARVAL_HOSTRose ; confirmed experimental for Allothrombium fuliginosum; on this host produce smaller despite larger host size
Hyadaphis sp. - LARVAL_HOSTHoneysuckle ; confirmed experimental for Allothrombium fuliginosum
Tetragnatha sp. - LARVAL_HOST ; for Trombidium brevimanum
Enoplognatha ovata - LARVAL_HOSTCandystripe ; for Trombidium brevimanum
Xysticus ulmi - LARVAL_HOSTCrab ; for Trombidium brevimanum
Palomena prasina - LARVAL_HOSTGreen ; for Trombidium holosericeum
Panorpa communis - LARVAL_HOST; for Trombidium holosericeum
Rhagonycha fulva - LARVAL_HOST; for Trombidium holosericeum
Javesella sp. - LARVAL_HOST ; for Trombidium heterotrichum

Life Cycle

Complex with seven stages typical of Parasitengona: , prelarva (inactive), (active, parasitic, 5-8 days duration), (inactive, quiescent, calyptostatic), (active, predatory), tritonymph (inactive, quiescent, calyptostatic), and (active, predatory). Success of from protonymph to deutonymph was 49-57.5% depending on . Marked heteromorphism between larval and postlarval forms.

Behavior

actively seek and attach to dorso- or , or thorax- border; 1-3 larvae per host observed. are active that refuse to stop moving, making them difficult photographic subjects. No microhabitat segregation observed among syntopic .

Ecological Role

function as of and , potentially contributing to segregation among syntopic congeneric through differential exploitation. and serve as of small . Some species have potential as agents for pests.

Human Relevance

made from Trombidium grandissimum is used in traditional Indian medicine. Harmless to humans despite large size of some . May be encountered by gardeners and naturalists in soil and litter . Spiderlings of some species subject to by trombidiid in natural settings.

Similar Taxa

ErythraeidaeAlso parasitic on ; distinguished by different structure and typically less dense setation
Other Trombidioidea familiesRequire examination of in view for definitive separation; many former trombidiid now elevated to rank

More Details

Systematics

The of Trombidiidae has been in flux; many former have been elevated to rank within Trombidioidea. identity often requires COI sequencing and species delimitation tools (ABGD, ASAP) combined with phylogenetic inference.

Intraspecific Variation

identity significantly affects in Allothrombium fuliginosum. parasitizing Macrosiphum rosae produced smaller deutonymphs despite this host having larger body size, indicating factors other than host size influence development.

Laboratory Rearing

Successful laboratory rearing uses plaster/charcoal substrate at 22°C (day), 15°C (night), 80% humidity with 12:12 hour .