Giant Emerald Pill-Millipede: when these enormous millipedes are all rolled up, their bodies can be as big as a baseball, a tennis ball, or a small orange
This species (Zoosphaerium neptunus) is commonly known as a giant emerald pill-millipede. The females can measure up to 90mm long (roughly 3.5 inches), making this the largest species of pill-millipede in the world.
There is a significant degree of sexual dimorphism in this species, with the males measuring only about 45mm (1.8 inches) long -- roughly half the size of the females.
Giant emerald pill-millipedes are found only in Madagascar, which is home to several endemic species of giant pill-millipedes (order Sphaerotheriida). The Malagasy name for giant pill-millipedes is "Tainkintana," which means "shooting-star."
Pill-millipedes use conglobation as a defense mechanism, which means that they can curl their bodies up into a spherical shape so that their dorsal plates form a protective shield around the softer, more vulnerable parts of their bodies, just like an actual pill-bug or a "roly-poly."
When they roll themselves up completely, they look almost like gently polished chunks of malachite, emerald, or jade.
Giant emerald pill-millipedes will sometimes form large swarms that travel together as a group. This is the only species of giant pill-millipede that engages in any sort of swarming behavior, and the purpose of that behavior is still unclear. The swarms often contain thousands of individuals, with almost all of them moving in the same direction, even when there is no physical contact that might allow the millipedes to "herd" one another along.
Their swarming behavior also has some very peculiar features, as this article explains:
During swarming, Zoosphaerium neptunus individuals pay little attention to their surroundings; many specimens were observed walking straight into and drowning in small puddles. Some swarms even display ‘cliché lemming behaviour:' in Marojejy, a large part of a swarm walked into and drowned in a small river.
No single specimen was observed walking ‘against the current,' all specimens were moving in the same direction (southeast), even when not in contact with one another.
Of 273 randomly collected individuals, 105 were males, while 168 were females. The males were 8.3 - 14.1 mm wide (average width 10.4 mm). According to the inner horns of the posterior telopods, all males were sexually mature. The females were 9.95 - 15.4 mm wide (average
width 11.4 mm). All females displayed non sclerotized vulvae and were sexually immature.
Some researchers argue that the swarming serves as a defense mechanism, providing a layer of protection (or at least some cryptic cover) against local predators, but the swarming behavior is still poorly understood.
Important Note: I just want to remind everyone that these animals belong in their own natural habitat -- they should not be trapped, bought/sold, traded, shipped, collected, or kept as pets. This particular species does not survive well in captivity, either, and the demand for these "exotic" invertebrates is putting the wild populations in jeopardy. The previous article discusses those issues, too:
Another possible threat for Z. neptunus swarms are collections for the pet trade. There exists a large demand in Japan, Europe and North America for 'green -eyed monsters’ as pets. Giant pill -millipedes from Madagascar unfortunately have a very short survival time in terraria. The species is specialized on low-energy food (dead leaves), and adapted to the cool climates (<20°C) of the highlands. Specimens in terraria often starve to death quickly.
So I know that they're adorable and really, really fascinating...but let's just let them be their chunky, adorable little selves out in the wild where they belong.
European Journal of Taxonomy: Seven New Giant Pill-Millipede Species and New Records of the Genus Zoosphaerium from Madagascar
Madagascar Conservation & Development: Swarming Behavior in the World's Largest Giant Pill-Millipede, Z. neptunus, and its Implication for Conservation Efforts
Bonn Zoological Bulletin Supplementum: The Giant Millipedes, Order Sphaerotheriida (an Annotated Species Catalogue) (PDF)
African Invertebrates: Madagascar's Living Giants: Discovery of Five New Species of Endemic Giant Pill-Millipedes from Madagascar (PDF)
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