The Giant Emerald Pill-Millipede: this enormous millipede can curl its body into a sphere, and it's roughly the size of a tennis ball or a small orange
Zoosphaerium neptunus, commonly known as the giant emerald pill-millipede, is the world's largest species of pill-millipede, with females measuring up to 90mm long (roughly 3.5 inches). The size of its rolled-up body is often compared to a baseball, a tennis ball, or a small orange.
The males are roughly half that size, measuring only about 45mm (1.8 inches) long.
This species is found only in Madagascar, which is home to several other endemic species of giant pill-millipedes (order Sphaerotheriida). In the local Malagasy language, giant pill-millipedes are also known by the name "tainkintana," which means "shooting-star."
Pill-millipedes use conglobation as a defense mechanism, which means that they can curl their bodies into spheres, with their dorsal plates forming protective shields around the softer, more vulnerable parts of their bodies, just like pill-bugs or "roly-polies."
When their bodies are completely rolled-up, they look almost like gently polished chunks of malachite, emerald, or jade.
Giant emerald pill-millipedes have also been known to form large swarms that travel together as a group. This is the only species of giant pill-millipede that engages in any type of swarming behavior, and the purpose of that behavior is still unclear. The swarms often contain thousands of individuals, and almost all of them move in the same direction, even when there is little to no physical contact that would allow them 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.
I 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 "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.
Sources & More Info:
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)
