As natural as it is, it’s kind of amazing that the human body can create and excrete a special kind of food to keep a baby alive and healthy without any other input. And we’re hardly alone: mammals as a class are the fact that they have boobs with which to feed their young.
But here’s the thing: milk can get weird. From lactations that are closer to butter than milk, to cream cheese thrown up by a bird, to superbug-killing sweat, there’s more to the pint in your refrigerator than meets the eye. Here are some of the strangest.
Platypuses: sweatiest milk
You can’t talk about weird animal milks without mentioning platypuses and their puggles. See, unlike most mammals, platypodes don’t have nipples with which to suckle their young – so their bodies do the next most obvious choice, and simply ooze milk from the surface of their skin, like sweat.
Hungry platypups will then from where it’s collected in the grooves in their mother’s skin, or suck it up from their fur. It’s gross to think about, and not very nice from a hygiene perspective either – which is actually what makes it so interesting to scientists hoping to discover the next generation of antibiotics.
“Platypus are such weird animals that it would make sense for them to have weird biochemistry,” said Janet Newman, a scientist at Australia’s national science agency CSIRO, in a . Newman was lead author on which, in 2018, discovered a unique protein structure in platypus milk that makes it particularly good at fighting harmful bacteria.
“By taking a closer look at their milk, we’ve characterized a new protein that has unique antibacterial properties with the potential to save lives,” she explained. Dubbed the Shirley Temple – due to its ringlet-like appearance – it’s hoped that this substance might give humans an edge over antibiotic-resistant superbugs that are on the horizon.
Not bad for an animal that was .
Hooded seals: fattiest milk
All milk has some fat content, but exactly how much of the liquid is lipids can vary way more than you may think. Take the black rhinoceros, for example: if they weren’t critically endangered, they’d be a boon to the diet industry, as they naturally produce milk that is just around 0.2 percent fat – than you’d find in “nonfat” milk from the store.
Then there’s the hooded seal. These blubbery mamas only nurse their pups for around four days, but they sure pack a lot in during that time: their milk is more than 60 percent fat – nearly twice as much as is in heavy cream. By drinking around 10 liters of the stuff per day (to put that another way, around twenty times what a human newborn takes from their mother) the baby seals are able to pack on about 7 kilograms (15 pounds) in that half-a-week of life, or roughly 30 percent of their birth mass every day. It would be as if an average human baby had zobbed up to 10 kilograms (22 pounds) by the time they were four days old.
Not that such a huge weight increase would be surprising if you were putting away the calories a newborn hooded seal does. “[The] gross energy content of hooded seal milk is 5.9 kcal/g,” notes on pinniped lactation, and “Milk energy consumption is 60,000 kcal (251 MJ) per day.”
“This energy consumption equivalent would be similar to a 6-year-old human […] consuming 109 McDonald’s Big Mac[s] per day for 4 days,” the authors add, “although the fat percentage would still be less than hooded seal milk.”
Pigeons: crop milk
All mammals make milk, but not everything that makes milk is a mammal. Pigeons, for example, are one of that produce crop milk, so called because it comes out of the crop – a little pouch at the base of their throat that’s used to store food before it gets digested.
Now, we know what you’re thinking: that sounds more like puke than milk. But don’t let the origin point fool you – pigeon crop milk is closer to boob milk than you might think, both in its production and its composition. Like in mammals, it’s stimulated by the hormone prolactin and is the only food a newly hatched birb will consume. And it’s seemingly perfectly designed to nourish a developing squab or chick – so much so that when scientists tried to replicate the concoction in the 1950s, mimicking the fat-protein-carb-mineral makeup as best they could, the baby birds regardless.
We now know that pigeon milk contains specific antioxidants and immune-boosting antibodies – properties that don’t only benefit the babies. “It is possible that […] they are directly enhancing the immune system of the developing squab as well as protecting the parental crop tissue,” noted Meagan Gillespie, a researcher at CSIRO Livestock Industries, Australian Animal Health Laboratory, in a back in 2011. And it seems like this particular bird has more or less perfected the recipe, too: give pigeon milk to chickens, and their by nearly 40 percent.
So why aren’t we all rushing out to the London Underground, milking stools at the ready? Well, pigeon milk can’t exactly be poured onto cereal or into a morning coffee: it’s or cottage cheese than your regular half-and-half. Plus, of course, it’s only produced by parent pigeons for about ten days, so the milking time would be extremely short.
One saving grace? Pigeons are apparently equal-opportunities parents, with both mommy and daddy birds producing this yummy regurgitation. Now that’s co-parenting.
Jumping spider: creepiest milk
Look, we don’t want to hear about how spiders are actually cute or whatever: the fact is, there’s a reason that movies with names like Arachnophobia and Eight Legged Freaks are listed under “horror” while Kung Fu Panda is a “family comedy”. Spiders may be an interesting and unique branch of the evolutionary tree, but cuddly they are not.
That said, there is at least one species of arachnid which is, if not actually cute, then something approaching it. , Toxeus magnus, a jumping spider that looks uncannily like an ant, was found to not only produce milk for its baby spiderlings, but to continue to care for its offspring for a period that rivals humans for its longevity.
It’s a , as well: mama jumpers can lay up to 36 eggs at a time, and they start feeding all of them drops of milky goodness as soon as they hatch. While at first, this is a hands-off (pedipalps-off?) process, with the mother depositing little bits of milk around the nest for hatchlings to find, it doesn’t take long before all the baby spideys are lining up at their mother to feed, like little semi-demonic piggies.
Like its mammalian equivalents, jumping spider milk contains fats, sugars, and proteins – in fact, it’s about four times as protein-rich as cow milk. But you probably wouldn’t want to drink it: we’re not quite sure how it’s made, but one leading theory is that it’s the liquified remains of eggs that failed to mature properly. Delicious.
Hippos: (not) pink milk
Kind of a cheat, this one: the interesting thing about hippo milk is that it’s… pretty normal, actually.
Why is that noteworthy? You may have heard a that hippo milk is pink – the strawberry milkshake of the natural world, if you will. And it’s not like the beasts don’t have form on this: they’re already renowned for their “blood sweat” – a secretion which is neither blood nor sweat, but more like a natural sunscreen and antibiotic that gives their skin a rosy sheen when they get hot under the sun. So sure, maybe they make pink-hued milk as well.
Well, no. Like all mammals, the milk of hippos is white, or at least white-ish. It’s not entirely clear where the concept of it being pink came from – though it’s had some endorsing it – but the best guess is that maybe someone saw the milk mixed with a bit of sweat, and assumed the resulting color was the milk alone.
But “while [that’s] possible, it’s also pretty unlikely, as baby hippos are very efficient eaters,” explains . “They grip mom’s nipple between the tongue and the roof of the mouth, forming such a tight bond that they can even nurse underwater if they wish.”
“Reports of actual pink milk are limited not only by the low odds that these two fluids will mingle, but also thanks to the difficulty of getting a close look at the hippo’s feeding process,” they add. “Female hippos are most likely to attack when they are pregnant or taking care of their young, and few are brave enough to tangle with a mad 3,000-pound (1,361-kilogram) momma just to get a glimpse of her milk.”