Entomological Etymology 4: exoskeletons, development, the clonal raider ant
This time, we’re talking chitin, molting, development, and the clonal raider ant.
Insect exoskeletons are not made of bone, but “chitin,” a fibrous sugar chain chemical. “Chitin” comes from a Greek word meaning ”tunic” or “coat” -- as in a coat of mail. Which makes a lot of sense, since the chitinous exoskeleton protects the soft body inside.
Chitin was first discovered in mushrooms, where it is found in the fungal cell wall, allowing mushrooms to grow vegetative bodies that look like plants. But in plants, the cell wall is chemically completely different, made of cellulose instead!
Lots of critters use chitin for structural support and defense, notably crustaceans, the cousins of the insects. These guys can really lay it on thick, just to keep you away from that delicious lobster meat...
Insects are protected by their chitinous exoskeleton, but unlike skin it’s inflexible, and so insects need to molt their exoskeleton before growing bigger (and then hardening up again).
Molt means - “to shed or fall out”. This word has been in English for a while, as far back as Old English “mutian”. That word came to English from Latin “mutare” pretty early on in English history, and has several cognates that have entered English later on - like “mutate” meaning to change. These words trace back to the PIE root “mei-” meaning to change or go, which has ended up in the word common: “co-” -“mun” to go together. From this root we get so many English words, like “communicate” and “communism”.
I’m wary of imposing human social structure onto other critters, but you have to admit that some bugs are shockingly good at both communication and communal living - especially social insects like ants, termites, and many bees and wasps.
Bugs communicate in their own species-specific way, often through sounds or chemicals. Ants in particular use all kinds of chemical signals, or pheromone, to share information - trail pheromones on a surface indicate the way to food, while alarm pheromones puffed into the air mean “get ready for danger”. And pheromone comes from Greek “pherein” to carry, combined with the ending of “hormone”. Just like hormones are chemical signals that allow different body tissues to communicate, pheromones carry information between individuals!
As a growing insect molts, it’s said to progress from one instar to another - meaning developmental stage. Instar is Latin, meaning “likeness” or “image”. So we say that the clonal raider ant larva has four larval instars, meaning it goes through four different exoskeletons during its larval stage.
The final instar, the adult stage, is called the imago. Weirdly, imago and instar are synonyms in Latin, both meaning “likeness” or “image”. Imago comes from “imitari”, which also gives us “imitate”. The Proto-Indo-European root “aim-” is related to words like “image”, and “emulate”. By the way, I highly recommend Octavia Butler’s Xenogenesis trilogy of scifi novels. That’s “Xeno-” meaning foreign or alien + “genesis” meaning birth. The third entry in the trilogy is called Imago, and there’s some truly wild alien developmental biology in there.
In my experience, entomologists rarely use “imago,” probably because “adult” is just simpler. But the word still shows up in insect developmental biology: for insects that go through complete metamorphosis, from larva, to pupa, to adult, the progenitor cells that will form the adult body parts are already present inside the larva’s body, but dormant and undeveloped. They’re called the “imaginal discs”, referring to imago, and the fact that they’re disc shaped.
The insects that develop from larva, to pupa, to adult are called “holometabolous”, from Greek “holo”: complete, and “metabola”, meaning change. These creatures, like butterflies, ants, flies, beetles, really go through a total transformation during that pupal stage in the middle. Pupa, by the way, is Latin for doll, and gives us English “puppet”. I guess because the pupa is a bug that doesn’t move, almost like it’s a toy insect?
The more ancient insect lineages don’t make a pupa. The original way of doing things was basically just to get bigger with each molt, a lifestyle you see in the hemimetabolous insects: hemi, meaning partial -- like mantises, roaches, dragonflies, and aphids. They progress through a series of “nymph” stages, before reaching the imago. Nymph traces back to Greek, where it meant a young woman, a bride, or a demi-goddess. It might be related to “nuptial”, for marriage. Bug nymphs are true beauty and grace, am I right?
Species highlight:
For my PhD, I studied the clonal raider ant, Ooceraea biroi. This species is native to southeast Asia but has invaded tropical islands across the world. These ants are only around 3mm in length, and have an unusual social life for ants. They lack a queen caste: instead, the workers all lay eggs parthenogenetically, coming from Greek “partheno-” for virgin, and “genesis” for birth. Think of the Parthenon, the ancient Greek temple to Athena, virgin or maiden goddess.
Clonal raider ants are called such because they reproduce clonally, meaning each descendent is genetically the same as her mother. Clone comes from Greek “klon” meaning a twig or offshoot, referring to how plants can propagate descendents without needing to grow from a new seed.
And they’re called raider ants because we think they invade the nests of other ant species and collect their pupae for food!
The genus name “Ooceraea” from Greek “oo”, as in oocyte or “egg”, plus “ceraea” or “horn”. Greek didn’t have its own word for insect antenna, so antennae are effectively considered little horns. This root also gives us Rhinoceros, the nose-horn. Specifically, Ooceraea are named such for the final segment of their antennae, which is a bit egg shaped.
Just a few years ago, this ant species was placed in a different genus, called Cerapachys. That’s “Cera-” again horn, meaning antenna, and “-pachys”, meaning thick, like in pachyderm (that’s elephants, for their thick skin). So Cerapachys was the ants with thick antennae! Myrmecologists moved biroi to genus Ooceraea after learning more about the evolutionary relationships within this group of ants.
Biroi just refers to the guy who first described them in the early 1900s, the Hungarian zoologist (animal-studier) Lajos Bíró. So we have the clonal raider ant: The ant with egg-shaped antennae that Biro found.
Clonal raider ants, though tiny, have incredibly tough exoskeletons - probably because they’re armored up the dangerous business of raiding other ant nests!
Stay tuned for more Entomological Etymology. What types of bugs do you want to hear about next?
Words covered: chitin, molt, mutate, communicate, communism, pheromone, hormone, pherein, instar, imago, image, emulate, xenogenesis, imaginal discs, holometabolous, pupa, puppet, hemimetabolous, nymph, nuptial, clonal raider ant, parthenogenesis, clone, Ooceraea biroi, Cerapachys, pachyderm, rhinoceros
Sources:
