Volvation

{{Short description|Defensive reaction of certain animals}}

File:Caecosphaeroma en boule.jpg: two of three pillbugs have curled themselves into "pills"]]

Volvation (from Latin volvere "roll", and the suffix -(a)tion; sometimes called enrolment or conglobation) is a defensive behavior of certain animals in which the animal rolls its body into a ball, presenting only the hardest parts of its integument (the animal's "armor") or its spines to predators.

Among mammals, vertebrates such as pangolins (Manidae) and hedgehogs (Erinaceidae) exhibit the ability to conglobate.{{cite journal | vauthors = Sigwart JD, Vermeij GJ, Hoyer P | title = Why do chitons curl into a ball? | journal = Biology Letters | volume = 15 | issue = 10 | pages = 20190429 | date = October 2019 | pmid = 31573429 | pmc = 6832185 | doi = 10.1098/rsbl.2019.0429 }} Armadillos in the genus Tolypeutes (South American three-banded armadillos) are able to roll into a defensive ball, but the nine-banded armadillo and other species have too many plates to do so.{{cite web | language=fr | url=http://www.cnrtl.fr/definition/volvation | title=VOLVATION : Définition de VOLVATION | location={{ill|National Centre for Textual and Lexical Resources|fr|Centre national de ressources textuelles et lexicales}} | access-date=April 24, 2020}}.

Earthworms may volvate during periods of extreme heat or drought. Among pill millipedes, volvation is a protection against both external threats and against dehydration.{{cite book | language=fr | vauthors = Gobat JM, Aragno M, Matthey W | title=Le sol vivant : bases de pédologie, biologie des sols | volume=14 de Gérer l'environnement | publisher=PPUR Presses polytechniques | date=2010 | pages=817 | isbn=9782880747183 | url=https://books.google.com/books?id=zctE3re2NIoC | access-date=April 24, 2020}} At least eight families of flat-backed millipedes are known to practice true volvation; these are described as oniscoid (woodlouse-like).{{Cite journal |last=Golovatch |first=Sergei I. |date=2003-08-01 |title=A review of the volvatory Polydesmida, with special reference to the patterns of volvation (Diplopoda) |url=https://journals.co.za/doi/abs/10.10520/EJC84515 |journal=African Invertebrates |volume=44 |issue=1 |pages=39–60 |hdl=10520/EJC84515}}

The pauropod family Sphaeropauropodidae has the ability to coil completely into a tight sphere.{{Cite book |last=Minelli |first=Alessandro |title=The Myriapoda: Treatise on Zoology - Anatomy, Taxonomy, Biology |date=2011 |publisher=BRILL |isbn=978-90-04-18826-6 |edition=1st |series=Treatise on Zoology - Anatomy, Taxonomy, Biology - the Myriapoda Ser |location=Leiden}}

Woodlice or pillbugs (Armadillidae) curl themselves into "pills" not only for defense, but also to conserve moisture while resting or sleeping, because they must keep their pseudotrachaea ("gills") wet. Volvation is common for subterranean isopods, but only Caecosphaeroma burgundum is able to roll into a hermetic sphere without any outward projections.{{cite journal | vauthors = Marvillet C |title=Les adaptations à la volvation du squelette externe de la tête chez Caecosphaeroma burgundum Dollfus, Crustacé Isopode des eaux souterraines |url=https://scholarcommons.usf.edu/ijs/vol8/iss4/3/ |journal=International Journal of Speleology |year=1976 |volume=8 |issue= 4|pages=331–358 |doi=10.5038/1827-806X.8.4.3 |access-date=April 22, 2020|doi-access=free |bibcode=1976IJSpe...8..331M }} (Article has English abstract.)

Multi-shelled chitons also volvate, although evidence suggests that they do not use this behavior as an anti-predatory defense but rather as a form of locomotion.

In vertebrates, an animal's decision to volvate is mediated by the periaqueductal gray region.{{cite book | vauthors = Feinberg TE, Mallatt JM |date=2018 |title=Consciousness Demystified |url= |location=Cambridge, MA |publisher=MIT Press |pages=50–51 |isbn= | quote = ...the affective region called the periaqueductal gray signals the motor panic actions of fleeting, curling one's body into a ball for protection, sweating, and so on. }}