“I already have plans.” I hear myself allow that particular evasive phrase to slip out more as the weather warms and the squidding season arrives. Especially when someone tries to get me to drive off Cape. It’s only human.
But we humans aren’t the only ones to throw up smoke screens. Squid do it, too, with a blast of what we call “ink.” It’s not the burned-wood, bone-ash, and animal glue of old carbon inks or the soybean oil and pigments used in printing this newspaper. But throughout the ages, squid ink has been used for writing, printing, and other arts.
We call it ink because of its color. The black component comes from a molecule, a biopolymer, called melanin. Melanin is made on almost every branch of the tree of life, by bacteria and fungi, and by humans, too. It is what gives darkness to our hair and skin. It absorbs both visible light (therefore it appears black) and ultraviolet light (thus protecting us from harmful radiation).
The ink is made by the squid and exits its body through a siphon near its head. This is the same siphon the squid uses to squirt water to propel itself on a 25-mile-per-hour escape from predators.
But squid inking is not a simple release of diffuse blackness. The ink is commonly mixed with mucus and released to take on different shapes that appear to have purpose to ad inkd ink squid.
Scientists have noted puffs, strings, and what they call “pseudomorphs” — which, as the name implies, look like squid bodies in the water. The squid’s rope-like ink trails are not as well understood as the pseudomorphs, which clearly act as decoys. While a squid-shaped pseudomorph hangs right there in the water where the squid was, the real thing jets away.
Inking is what biologists call an “expensive” behavior. Making that ink and its associated mucus uses a lot of basic metabolic energy, so its use is saved for the most critical moments.
There’s more in that gemisch we call ink than just the melanin and mucus. And these extra bits seem worth analyzing. Some — such as dopamine, taurine, and glutamate —may be active in the squid’s world in ways we do not expect.
There is already research showing that predators, tasting ink, will calm their hunt. Is this from those bioactive elements giving them a sense of reward? Or is it due to some kind of foul-tasting — to sharks, at least — components that push the predators off?
We know that ink also warns conspecifics, which is a fancy scientist way of saying it tells other squid nearby to be on the lookout for predators. This kind of signaling can be especially useful at depths of water without enough sunlight to allow the squid to actually see the predator, or even the ink.
Squid ink is certainly something more than a visual shield, then, because inking does happen at darker depths.
The oldest sample of squid ink goes back long before humans ever walked the Earth, to the Jurassic period, 160 million years ago. Of course, squid go back much farther as a species, over 600 million years. Because they lack any bones or shells, squid are only rarely part of the fossil record. But in this one case, we got lucky. Chemists at the University of Virginia analyzed the 160-million-year-old ink sac of a well-preserved cephalopod. They found that the ink was not substantially different from what today’s squid make.
Which goes to show, if something works, Mother Nature doesn’t mess with it.