Not too long ago, I found myself writing a quick social media message for a seasonal organization that was shutting down for their off-season: a ski club, which has little or no activity between early April and early September.
The group was going dormant for a few months and a word that naturally came to mind was “hibernation.” In the first draft, something along the lines of “we’ll see you in the Fall, when we emerge from hibernation“ made it to the page.
As soon as I wrote that, I was pretty sure it made no sense. My Latin is exceedingly rusty, but I realized right away that this is a specific seasonal word. ‘Wait a minute,’ I thought. ‘”hibernation” means to sleep through the winter.’ It’s right there in the word — hibernate is from the Latin hiberna (winter quarters) or hibernare (to winter — a verb which isn’t much used in modern English). The Latin for ‘winter’ itself is hiems, if you’re curious.
What then, I wondered, is the correct term? Is there an opposite to hibernate…to describe what an animal does when it sleeps for the summer? Before I could even look that up, new questions followed: hibernation seems a natural strategy for an animal to reduce energy use and go dormant when resources are scarce. Are there reasons why an animal might want to sleep through the summer? And are there any such animals? What are they?
There are answers to all those questions.
First, there is an opposite to hibernate: it is aestivate (or estivate), and it means “to pass the summer, or any prolonged period of hot or dry conditions, in a state of torpor or suspended animation” (OED’s definition). Where hibernate derives from hibernare, aestivate comes from aestivare, ‘to (spend the) summer.’ [For simplicity and American English standardization, I’ve used the “estivate” form throughout the rest of this post, except where it makes a difference.]
Implied in the definition of estivate is the reason why estivation might be a useful evolutionary strategy: it allows an animal to suspend activity when conditions become too hot or too dry. In the same way that a hibernating animal cuts back when food is scarce (or when the weather is cold), an estivating animal isn’t using water when there isn’t much to be found (or it’s hiding away in a suspended state while hot weather makes activity too biologically costly).
Estivate is a relatively new word — the first citation (in the form “aestivation“) is credited to Charles Darwin in his 1839 account of his voyage on the HMS Beagle. Its recent coinage might not be too surprising. It also turns out that hibernate is nearly as new: first use, in the sense we care about, was in an 1816 entomology text. Of course, animals were known to hibernate before this word was coined, but a specific word, to label a specific biological process, hadn’t been needed before that time. The ‘Age of Enlightenment’ was just (technically) drawing to a close in England at this time (…England often being late to the party on larger European trends…such as the plague). An increasing interest in scientifically categorizing the world and all the phenomena in it also brings the need for new words. It’s no surprise that interest in words themselves took off during this same period and that the first modern dictionaries — Johnson’s (in England) and Webster’s (in the US) — were compiled and achieved popularity in the same general time period (the more comprehensive OED project would be launched soon after, in 1857).
What are some animals that estivate? There are enough to make the word useful. Numerous reptiles and amphibians estivate, including some tortoises, salamanders, and frogs. Some land snails do it. A few insects and some types of crab do it. It’s rare in mammals, with only one species of lemur and (maybe) an African hedgehog known to do it. The most often cited example of estivation is the lungfish, several species of which burrow into the ground and create protective cocoons to wait out the dry season. It’s something of a legend that lungfish can survive like this indefinitely, but they usually only estivate for a few months, until the next rainy season. One reference suggests that lungfish can remain in this state for up to four years, but beyond that would be difficult: their form of estivation requires slowly using up their own muscle mass.
I won’t bore you with all the shaggy details of how the word ‘estive‘ (‘aestive‘) and its variants moved into English from Latin, but it looks like it was a pretty typical migration. Some variety of the word can be found at least from the late 14th century (OED’s earliest is a 1386 use of ‘estival‘ — ‘relating to summer or the summer solstice‘). For this discussion, we’re only interested in the zoological definitions of hibernate and estivate.
Sometimes I think it would be nice to estivate and take the hottest part of the summer off. In my case, however, all estivation usually means is that my skis get a good coat of storage wax and all that gear goes into a corner of the basement until around Thanksgiving. If it were alive, we could say that our winter equipment gets to estivate, but not us.
Maybe by reading about estivate you’ve learned a new word. You might use it to impress your friends and annoy your rivals, or you might never speak it aloud. It’s still a good word to know, and I firmly believe that simply knowing more vocabulary, even if you never get to use it, makes you a more interesting person.