Turns out these Myrmica scabrinodis pupae, captured here with a scanning electron micrograph, have something to say. Credit: Luca Casacci et al., Current Biology (2013) via ScienceNow (dimensions modified to fit)
As Charles Darwin developed his theory of natural selection that formed the basis for The Origin of Species, he encountered "one special difficulty" along the way, he writes, that "at first appeared to me insuperable, and actually fatal to the whole theory."
It wasn't the myriad designs found on butterfly wings, or the complex songs of birds. It was ants.
Why, specifically, Darwin wondered, were some female ants born sterile? Why was nature willing to forfeit these ants' reproductive rights for the sake of the colony, when natural selection was all about propagating one's own genes? His hypothesis was that selection can operate at the family level, not just for individuals. Having neuter worker drones—even neuters of multiple castes within the same species—was advantageous to the family and, thus, favored by natural selection.
Other theories have emerged since then. What hasn't changed is that fact that ants, like humans, are one of the very few animals on earth that are "eusocial"—that's to say, as described in a recent Atlantic article, "the most highly social creatures in the history of life on Earth, capable of building complex societies in which individuals specialize in various activities and sometimes altruistically."
Complex, socially-tiered societies require complex communication. So perhaps it's unsurprising that eusocial animals like ants are also incredibly communicative—more so than we previously understood, according to a new study in Current Biology. Many ants begin communicating acoustically from a very young age, in fact—in a way scientists suggest may be very important to their social lives and survival.
As explained in an article by Carrie Arnold at ScienceNow, scientists believed until only recently that ants communicated only through pheromones, leaving, for example, scent trails behind them for other ants to follow—hence the phenomenon of single-file marching ants. (They can also, newer research suggests, use magnetic and vibrational landmarks to guide themselves around.)
But scientists also noticed recently that some species of ant communicate by making noise, as well. You just had to listen really, really close. From observing the ants' behavior, it seemed clear that the sounds served as an alert whenever they were feeling threatened.
Mature ant pupae, on the other hand, despite possessing the same sound-making organs on their bodies (a kind of comb-like protrusion), were believed not to stridulate—the term for when an insect makes noise by rubbing its body parts together, like crickets do. But that didn't make sense. Why would they have these organs but not use them?
As it turned out, you just had to listen even closer. As Arnold describes it:
Karsten Schönrogge, an entomologist at the Centre for Ecology & Hydrology, Wallingford, in the United Kingdom, thought it odd that mature pupae would have the capability to produce sound but remain silent. So he and his colleagues listened in to a group of Myrmica scabrinodis ants…
Using an extra-sensitive microphone that would pick up on the faint acoustic signals, the researchers measured the sounds produced by 10 different M. scabrinodis larvae, six immature pupae, and six mature pupae. Whereas the larvae and immature pupae were completely silent, the mature pupae produced brief pulses of sound … Further analysis of this noise showed that it was a simplified version of the more complex adult sound. It was as if the mature pupae were saying, "Help!" while the adults were saying "Hey, I'm over here! Please come help! It's your friend!"
Embedding the audio files from the ScienceNow article has proved impossible, but follow the link here to listen to them at will. In the meantime, some kind internet soul who goes by "Stefano Di Criscio" has made this YouTube video of those same audio files.
The sounds made by mature ant pupae serve two functions, the research suggests. The first, as indicated above, is to signal alarm. Researchers found that fellow ants respond the same way they respond to more complex noises made by adults.
The second is more strictly social: it helps the ants in the colony identify the pupae as deserving of higher social status than their younger relatives, the larvae, who are, indeed, silent. The scientists found, in fact, that rendering the pupae mute resulted in a significant drop in their social status. It makes sense when we think of our own lives as humans, and the sudden elevated status we accord children when they can form complete sentences. Our interactions deepen. We make room for them in the dinner table conversation.
In other words, there's a reason we loved and rooted for Anty in Honey I Shrunk the Kids (who sounds an awful lot like these new audio recordings). They are incredibly complex, even selfless creatures. Like really, really, really small dogs.
RIP, Anty. Never forget.