Pilling in the name of

It’s about time I told you about pill bugs.

You would be forgiven for thinking I refer to some sort of oblong Hemipteran (i.e. true bugs, which the title “bug” should truly accord with). The reality is that I could be referring to one of two quite taxonomically distinct animals.

One would be forgiven for confusing the pill woodlouse Armadillidium vulgare and the pill millipede Glomeris marginata. Both are found in damp, often decaying surroundings, and both have the propensity to curl into a ball and hide from the world when things get tough (these possibly applicable to many edgy teenagers too). To make matters worse, they look remarkably similar, with even some entomological eyes mistaking the two. They can be distinguished by general shape and colour, legs, the millipede forming a more perfectly closed “pill” than the woodlouse, etc., but these aren’t necessarily easy to spot for the untrained eye. Given the tongue-twisting rollercoaster that is “Armadillidium” for the non-Latin-speaking lay populace, common names for these common species seem sensible, but why not different common names?! Well, that’s a little complicated. Compounded further by many more woodlouse species sharing the same name. Correction: the same many, many names.

I would be lying to say that this post wasn’t inspired by Jennifer Myers‘ recent tweet about woodlouse names, and the swirling storm of Isopod fanatics that responded to it. I have, however, fascinated over this topic since the age of about 10, so gladly took the opportunity to delve deeper than I’ve ever (publicly) delved before.

Woodlice, or isopods, belong to an order of crustaceans (Isopoda) best-known for their humongous marine members (e.g. Bathynomus giganteus), but also their successful colonisation far onto the land, unlike most of their highly water-dependent relations (e.g. crabs, barnacles (yes, they are crustaceans), shrimp). That said, they aren’t alone, with the lawn shrimp Arcitalitrus sylvaticus also joining their terrestrial jaunts. To redress their unquenchable thirst, most terrestrial isopods stick to damp, dark places; whilst most arthropods have a waxy cuticle, isopods are often constrained by a primitive water-based lung-like system.

The lawn shrimp Arcitalitrus sylvaticus.

Despite many woodlice being lumped in with Armadillidium and Glomeris species as “pill bugs” by the average passerby, most woodlouse species can’t perform the distinctive roly-poly manoeuvre responsible for their branding. Here lies the problem: woodlice are mostly very similar to the lay observer, thus sharing common names. But not just one. Nor two. Nor ten. NOR EVEN FIFTY.

Woodlice have inspired generations across continents to rattle off name after name, each mostly with a surprisingly tight regional distribution. Whilst some are deducible and related to their ecology, such as woodlouse, and others refer to their appearance, such as armadillo bug or slater (presumably a reference to their slate-like colour scheme or lack thereof), there are many more obscure examples, like tiddy-hog and shoemaker. Interestingly, a sort of etymological taxonomy can be observed, with “pig” and “hog” variants splitting into tightly-associated sets like “chuggy”, “chiggy”, “chooky” and “chucky” pigs, implying an evolution by Chinese-whisper-like inheritance of terminology. This never-ending name list has been regularly raised in popular scientific conversation for decades, perhaps centuries, as evidenced by Walter E. Collinge’s letter to Nature in 1917.

Walter E. Collinge’s communication with Nature in 1917.

Having spent the early years of my life in Scotland, the name “slater” was commonplace for me. As I trickled down the UK over the subsequent decade, I came to appreciate the simple title “woodlouse”, whilst many school-friends would employ the more jovial “chucky pig”, the realisation of which frustrated me greatly. “How can we have a conversation about the same thing whilst referring to it so differently?!” But therein lies the beauty (and curse) of common names. What’s in a name, after all? So long as it serves as a useful identifier of something, it hardly matters what name is used. But, at least for invertebrates, they so often overlap with other species, sometimes very distantly-related, taxa. This propagates confusion and chaos. Consider for a moment the confusion of a highly destructive invasive ant, such as Pheidole megacephala, with a common cosmopolitan species like Lasius niger. Endless reports of imminent ecosystem meltdown later, a distinction would have to be made. Whilst confusing two woodlice is hardly going to cause a catastrophe, a precedent should be set that can be applied across the biological sciences.

What does this mean for our other pill bug, Glomeris marginata? Perhaps the difficulty in distinguishing these two distant species could be alleviated if we weren’t all teaching every subsequent generation to call them the same thing (thus subconsciously feeding the concept that they are synonymous). But which do we call the pill bug then? My preference is neither (especially since neither is strictly a bug), opting instead for the classic millipede vs. woodlouse, but that’s not to say I can’t recognise the cultural value in these limitless labels. Through woodlice, we can recognise linguistic and cultural evolution in action.

Interestingly, however, I have yet to hear the many monikers of woodlice surface in the context of the pygmy woodlice (Trichoniscidae), such as Androniscus dentiger, despite being the most abundant isopods, at least in Britain. Perhaps their miniature bodies will remain mostly buried in the soil until this whole business blows over.

The rosy woodlouse Androniscus dentiger.