Armadillidae

Brandt in Brandt & Ratzeburg, 1831

Tropical Pill Woodlice, Pill Bugs

Genus Guides

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Armadillidae is the largest of terrestrial isopods (woodlice), comprising approximately 80 and 700 . Members are characterized by their ability to enroll into a complete sphere (conglobation), a defensive that distinguishes them from most other woodlice families. The family exhibits a strongly convex body form adapted for this rolling behavior, with fully enclosed within the sphere when enrolled—a key difference from the superficially similar family Armadillidiidae. Armadillids occupy diverse across tropical and subtropical regions worldwide, with some species adapted to arid environments and others to cave systems.

Venezillo pisum by no rights reserved, uploaded by Alan Jeon. Used under a CC0 license.Venezillo parvus by (c) Even Dankowicz, some rights reserved (CC BY), uploaded by Even Dankowicz. Used under a CC-BY license.Venezillo parvus by (c) Even Dankowicz, some rights reserved (CC BY), uploaded by Even Dankowicz. Used under a CC-BY license.

Pronunciation

How to pronounce Armadillidae: //ˌɑːr.məˈdɪlɪdiː//

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Identification

Distinguished from Armadillidiidae by complete enclosure during conglobation. Distinguished from non-conglobating by ability to form perfect sphere. Some secondarily lost conglobation through reduction of inner coxal plate ; males of such species cannot enroll. Cave species identifiable by reduction, pigment loss, and appendage elongation.

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Habitat

Forests, savannas, and arid regions; some in deserts with physiological adaptations to heat and low productivity. Multiple independent cave-dwelling lineages exist, including troglobitic species in Colombia (Diploexochus troglobius) and Vietnam (Dryadillo longiantenna).

Distribution

Native to Afrotropics, Asia, Australia, Neotropics, and Mediterranean Europe. Few native in North America north of Mexico; some introduced elsewhere. Specific documented localities include Southwest Desert Province of North America (Venezillo arizonicus), Colombian Caribbean, New Caledonia, Flores (Indonesia), Myanmar, Seychelles, Izu Islands (Japan), and karstic islands in North Vietnam.

Behavior

Defensive conglobation (rolling into sphere) is primary ; some have secondarily lost this ability. Mating in studied species (Venezillo evergladensis) involves male antennal tapping of female, female assuming receptive posture with body lowered and uropods spread, and male mounting with sperm transfer via copulatory stylets on pleopods 1–2.

Human Relevance

Some collected for pet trade, with at least some Merulanella species considered endangered due to this pressure yet not formally listed by IUCN. Introduced established in some regions outside native range.

Similar Taxa

  • ArmadillidiidaeAlso conglobate into sphere, but remain partially exposed when enrolled rather than fully enclosed; most familiar 'pill bugs' in temperate regions belong to this , not Armadillidae.

Misconceptions

The 'pill bugs' is often applied indiscriminately to both Armadillidae and Armadillidiidae; these are distinct with different geographic distributions and morphological details. Most temperate 'pill bugs' encountered by casual observers are Armadillidiidae, not Armadillidae.

More Details

Taxonomic History

erected by Johann Friedrich von Brandt in 1831. Karl Wilhelm Verhoeff described nearly 25% of currently recognized (17 of ~80). Most armadillid are not monophyletic, indicating substantial revisionary work remains.

Physiological Adaptations

Desert-adapted Venezillo arizonicus shows critical thermal maximum of 43°C, 1.6–2.6°C higher than mesic ; possesses efficient pleopodal lungs enabling metabolic regulation in hypoxia down to 2% O₂; metabolic rate markedly lower than mesic relatives (1.5 vs. 4–6 μl min⁻¹ g⁻¹ at 25°C).

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