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Armadillidium

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Armadillidium
An Armadillidium granulatum in its roll-up stages.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Isopoda
Suborder: Oniscidea
Family: Armadillidiidae
Genus: Armadillidium
Brandt, 1833
Diversity
189 species

Armadillidium (/ɑːrmədɪˈlɪdiəm/) is a genus of the small terrestrial crustacean known as the woodlouse. It is one of 18 genera nested within the family Armadillidiidae[1]. Armadillidium are also one of the groups commonly known as pill woodlice, leg pebbles, pill bugs, roly-poly, or potato bugs, and are often confused with pill millipedes such as Glomeris marginata. They are characterised by their ability to roll into a ball ("volvation") when disturbed.

Distribution and habitat

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They chiefly feed on decaying organic matter like leaves, decomposed wood fibers, and less so on other organic material like lichens. They are usually found in moist areas such as decomposing leaf matter and soil. Armadillidium vulgare is the most abundant species in Europe and has been introduced worldwide. However, the vast majority of species are endemic to small regions close to the Mediterranean Sea, in much lower numbers than common species such as A. vulgare, and hence are understudied.

Description

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Unlike other terrestrial arthropods such as insects and spiders, pill bugs do not have a waxy cuticle that would reduce evaporation from their bodies. Pill bugs also use modified lungs, called pseudotrachea, for respiration, and the lungs must remain moist to function. Individual pill bugs typically live for two or three years, and females brood eggs once or twice each summer. In larger species and individuals, up to over an hundred eggs are brooded at a time in the marsupium, a pocket on the ventral side of the female pill bug. The marsupium provides nutrients and oxygen to the eggs until the hatch, resulting in a sort of “live birth”.

The colouration especially of young A. klugii resembles the red hourglass marking of the Mediterranean black widow Latrodectus tredecimguttatus. This is probably a kind of mimicry, to ward off predators that mistake the harmless animal for a venomous spider.[2]

Identification

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There are some morphological features that when seen together, help to identify members of Armadillidium from other closely related groups. These include[3][4] :

An image depicting Armadillidium vulgare and its component pieces.
The anatomy of Armadillidium vulgare as depicted in A Monograph on the Isopods of North America by Harriet Richardson
  • The ability to roll into a ball
  • convex oblong body shape
  • Multiple black ocelli (small, simple eyes)
  • size range of 5mm - 20mm
  • small first set of antennae, second set of antennae is approximately equal to half the length of the body
  • epistome passes the frontal edge, is vertically directed, and often triangular in shape
  • Short clypeus that is not lobate, and with a slightly wavy anterior margin towards the mid-line
  • end segment of the abdomen either triangular or rectangular
  • tracheae present on the opercular plates of the first two pairs of pleopoda
  • Short uropods


Species

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There are 189 recognised species in the genus Armadillidium:[5][6]

See also

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References

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  1. ^ Boyko, C.B; Bruce, N.L; Hadfield, K.A; Merrin, K.L; Ota, Y.; Poore, G.C.B. "WoRMS - World Register of Marine Species - Out of scope". www.marinespecies.org. Retrieved 2025-03-22.
  2. ^ "Revision of the Armadillidium klugii-group (Isopoda: Oniscidea)" (PDF). Archived from the original (PDF) on 2017-04-07. Retrieved 2015-07-29.
  3. ^ Hopkin, Stephen (1991). A key to the woodlice of Britain and Ireland. Environmental understanding for all. Field Studies Council (Great Britain) (First ed.). Shrewsbury: Field Studies Council. ISBN 978-1-85153-204-9.
  4. ^ Richardson, Harriet (1905). "A monograph on the isopods of North America". Bulletin of the United States National Museum (54): i–727. doi:10.5479/si.03629236.54.i. ISSN 0362-9236.
  5. ^ Helmut Schmalfuss (2003). "World catalog of terrestrial isopods (Isopoda: Oniscidea) — revised and updated version" (PDF). Stuttgarter Beiträge zur Naturkunde, Serie A. 654: 341 pp. Archived from the original (PDF) on 2009-02-24. Retrieved 2008-05-22.
  6. ^ "Armadillidium". WoRMS. World Register of Marine Species.
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