Milk-Like Nourishment in Non-Mammalian Species

Milk-like nourishment in non-mammalian species

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When we think of animals feeding their young, we often imagine mammals. The females in this group of animals are equipped with mammary glands that produce milk to sustain the young, but this isn’t the only way that Mother Nature has provided creatures to feed their offspring.

In fact, there are many other animals outside of the mammalian family that are able to produce natural nourishment. Some of these include birds, amphibians, and even fish.

While the substances they produce may appear to be milk-like, their composition is quite different. Depending on the species, this ‘milk’ may contain various nutrients that are essential for growth and development.

Non-Mammalian Milk-Like Producers in the Animal Kingdom

Did you ever think that a great white shark could produce milk for its young? Perhaps a flamingo or even types of beetles? While what these animals produce isn’t exactly milk in the sense that we understand it, it’s nourishment nonetheless.

1. Pigeon & Dove (Family Columbidae)

Pigeon and doves produce crop milk which is a nutritious substance containing fats (32%), proteins (60%), and carbohydrates as well as a series of minerals.

Can you milk a bird? Apparently so if it’s a pigeon or a dove. But it’s not the same kind of milk produced by mammals. It’s called crop milk which is a nutritious substance containing fats (32%), proteins (60%), and carbohydrates as well as a series of minerals that birds from the Columbidae family produce to feed their offspring. It’s considered one of their unique adaptations.

Interestingly, unlike mammals, both male and female parents are responsible for the production of crop milk, which is formed in a pouch known as the crop. This pouch in the esophagus has a lining that is capable of producing a secretion that the bird then regurgitates and feeds to its young. What’s even more amazing is that this secretion is only produced when chicks are in need of this type of nourishment and, just like mammals, is a part of the overall reproductive process.

When a female lays a clutch of eggs, they all hatch around the same time. Both parents play an active role in raising the chicks and, as such, are both able to produce crop milk. Without this nutrient-rich substance, chicks would not thrive as it provides just the right components for health development and growth. During research, birds fed with pigeon crop milk showed a faster rate of growth and, while the adaptation of milk production in pigeons and mammals was independent, the resulting products have very similar functions.

However, if you look at pigeon crop milk, you’ll notice that it bears very little resemblance to mammalian milk. It has a much thicker, lumpier consistency, which is said to be similar to cottage cheese.

As well as aiding in growth, crop milk is also essential for immune-system development and contains antibodies that help the young ward off disease.

2. Pacific Beetle Cockroach (Diploptera punctata)

The ‘milk’ produced by female cockroaches is used during the embryonic stages of development.

I know that most people would run away in horror when confronted by a cockroach; they’re not the most well-loved creatures on planet Earth. But have you ever considered drinking their milk? No, me neither, but according to research, cockroach milk actually has the potential for being a superfood.

This ‘milk’ is produced by female cockroaches and is used during the embryonic stages of development. But just like pigeon milk, it doesn’t look anything like the milk that humans produce. Instead, it’s more of a crystal-like substance. These tiny crystals contain important nutrients like sugar, fat, and proteins, which offer energy to the developing young. It’s thought that this is an adaptation to ensure as many young as possible survive. But, despite the myth, they still wouldn’t survive a nuclear blast!

Since cockroaches develop their young inside the body and then give birth to live offspring which are still in an early developmental stage, this milk is of the utmost importance.

So, what about that superfood business? Well, initially, the Pacific beetle cockroach caught the attention of scientists as being one of the few animals outside of the mammalian family to produce milk. But again, we have to consider that it isn’t necessarily milk as we would usually describe it. The term really relates to the natural production of a nutritious food source for offspring.

Where humans are concerned, there’s been a lot of attention surrounding cockroach ‘milk’ because of its high nutritional value. The substance contains high levels of proteins, amino acids, lipids, and sugars that hold a lot of health benefits. In fact, it’s thought that cockroach milk contains three times the goodness of cow’s milk!

But imagine trying to milk a cockroach! That’s where the problem lies since the size of the cockroach and the small amount of milk it produces makes it very difficult to harvest the product. Still, there are cockroach farms in countries like China, where billions of these insects are housed for milk harvesting.

3. Flamingo (Family Phoenicopteridae)

Flamingo milk has an impact on the coloration of these birds.

Earlier I talked about pigeon crop milk production, and flamingos produce a very similar product which is also known as crop milk. The main difference is that their crop is located in the digestive tract but again, both male and female members of this species have this special ability.

That’s a pretty important fact because flamingo parents are both equally involved in raising the young, so being able to independently feed them is essential to their survival. In many cases, the wider flamingo community would also play a role since these are social breeders; after all, they say it takes a village.

Believed to be an adaptation that allows flamingoes to successfully raise their young in a range of environments, crop milk production is actually affected by the adult’s diet. Being filter feeders, these aquatic birds eat small crustaceans and other organisms from the water and whatever nutrients they ingest will be present in the crop milk, which is then regurgitated and fed to the young. Although in any case, it’ll contain things like fats, proteins, and even red and white blood cells. Compared to pigeon crop milk, that of the flamingo is much fattier.

But what’s really interesting is that flamingo milk has an impact on the coloration of these beautiful birds. We all know that flamingos are pink, but did you know that it’s actually the carotenoids in what they eat that turn them this color? When they’re born, flamingo chicks are white. The crop milk has a red hue (thanks to the carotenoids) and, over time, this color is transferred to the chicks. If you observe a feeding adult, you may even notice that they look a little paler than usual as they’re passing on the carotenoids that alter their color to their young, causing them to fade.

4. Jumping Spider (Toxeus magnus)

Female jumping spiders are one of the only arachnids known to produce milk for their offspring.
Sarefo / Wikimedia Commons / CC BY-SA 3.0

The jumping spider has been a bit of a social media sensation over the last couple of years, with many people keeping them as pets. Certainly one of the more adorable spider species; and I say that loosely, they might be even more fascinating than you originally thought.

That’s because female jumping spiders are one of the only arachnids known to produce milk for their offspring. So full of goodness is this substance that scientists are saying it’s more nutritious than cow’s milk, with up to four times more protein. Still, I think I’ll give it a miss!

This phenomenon has been most closely documented in the Toxeus magnus species from Asia which is a spider that makes use of mimicry, looking like an ant. Females have been observed feeding their young droplets of this ‘milk’ that contains proteins, fats, and sugars to their young from a cavity in their abdomen.

What’s really interesting is that even though the offspring becomes self-sufficient after as little as a week, the mothers continue feeding them milk, even into adulthood. It’s thought that this is because the very presence of the mother ensures a greater chance of survival for the young.

5. Emperor Penguin (Aptenodytes forsteri)

Emperor penguins produce a special type of bird milk that contains up to 59% proteins.

You may be familiar with the fact the male emperor penguins are the primary carers for their offspring, keeping eggs and chicks warm while the females go off in search of food. But while they’re left holding the baby, they need a way to sustain it, and they do this by producing a special type of bird milk that contains up to 59% proteins.

Males have a crop in their esophagus where this milk is produced, and they’re able to make enough to feed their chicks for up to seven days. Just like other birds, once the milk is produced, the adult male will regurgitate it and offer it to his chick. Once mom returns from fishing, dad stops producing his crop milk.

6. Tsetse Fly (Glossina morsitans)

The female tsetse fly has the ability to produce a milky substance from a gland in her uterus.

The tsetse fly has got something of a bad reputation among humans because of its ability to spread diseases such as the African sleeping sickness, which can be fatal to humans. But let’s give them the benefit of the doubt and take a look at some of the more fascinating aspects of these insects.

Found across sub-Saharan Africa, the tsetse fly relies on the blood of other animals for sustenance. But when they are young, these flies rely on their mother to provide all the nutrition they need, and she provides this in a rather interesting way.

Like the cockroach, female tsetse flies give birth to live young who hatched from their eggs while still inside her. At this point, they have no way of taking care of themselves. So, mom has the special ability to produce a milky substance from a gland in her uterus, which she then passes onto her developing young. This boosts their development and allows them to safely enter their pupal stage after emerging from their mother.

If you look at a newborn tsetse fly, you’ll notice that it is pretty fattened up and that’s a result of all the milk it has ingested while still inside its mother. Some even say that if you squeeze it, all that milk comes flowing out. But that’s not something I’d recommend.

7. Discus Fish (Symphysodon spp.)

Within the mucus are high levels of proteins and other immune-boosting goodies that ensure the young are healthy and ready to face the world.

The discus is a popular aquarium fish, but if you’re an aquatic enthusiast, you may have noticed that these pretty fish care for their young in a very unique way. What’s more, this unusual form of lactation was not discovered until 1957.

So what happens? Well, the discus, unlike many other fish, does not abandon its young once they’re born. Instead, they hang around and start over-producing the mucus, which they usually secrete to protect their scales. Sounds gross but those discus fry think it’s a real feast!

Interestingly, studies have shown that the number of genes present in parenting discus fish is almost double that of their non-parenting counterparts.

Within the mucus are high levels of proteins and other immune-boosting goodies that ensure the young are healthy and ready to face the world (or ocean.) However, they’ve got something of a hefty appetite and will continue trying to feed off of their parents (yes mom and dad can do the feeding), in some cases, seriously harming them. That’s why it’s always important to separate them after the initial feeding frenzy is over.

8. Great White Shark (Carcharodon carcharias)

Mother great white sharks produce a fatty milk from the tissues in the wall of the uterus.

Tales of great white sharks attacking humans have given them one of the worst reputations in the animal kingdom. But these giants aren’t all bad. In fact, when you peel away that toothy facade, they’re actually some of the best mothers in nature.

Even before great white sharks are born, their mothers are producing a fatty milk from the tissues in the wall of the uterus. This substance remains in the uterus for much of the pregnancy and, at a later stage, turns clear. After this, the mother shark then released unfertilized eggs for her young to feed on before they hatch.

The uterine milk is highly nutritious and scientists, although only recently having discovered it, believe that it contributes to the successful growth of the embryo. During gestation, the presence of this milk can increase the weight of the offspring by up to 4900%, meaning that newborn sharks could be anywhere between 4.3 and 4.9 feet (1.3 and 1.5 meters) at birth!

9. Taita African Caecilian (Boulengerula taitanus)

During their gestation period, mother taita African caecilians will grow a new layer of skin which is packed with nutrients that her offspring can feed on.
Milvus / Wikimedia Commons / CC BY-SA 3.0

Did you ever consider feeding on your mother’s skin as a child? No, I didn’t think so, but while this may seem like an abhorrent thing to humans, it’s actually quite normal for the Taita African caecilian. While having a snake-like appearance, this is an amphibian species that gives birth to live young.

At any one time, females can give birth to between two and nine young and, during their gestation period, mothers will grow a new layer of skin which is packed with nutrients that her offspring can feed on once they’re born. This is a process known as maternal dermatophagy. This interesting adaptation is thought to have evolved over the course of 100 million years, and the young have even adapted special teeth called odontodes, which they use to nibble away at the special skin. 

Packed with important fats, this isn’t the only food source for the young. The female will also secrete fluid from her cloaca, which the young also ingest to boost development.

Found only in the Taita Hills of Kenya, this is a unique species and one that’s essential to the ecosystem thanks to its soil aeration activities.

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