The platypus do it, so it can and is done, some how. It would be a waste of energy to be lactating the entire time after the egg is laid up until it hatches, so how does my alien race know when to start?

The aliens are an odd mix between mammal and bird. The egg is about the size of an ostrich egg, but takes about 3 months to hatch, give or take a week. Would it be an instinctive timing thing, or would there be another trigger? I'm willing to use some fictional magic on this if need be.

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    $\begingroup$ The same way extant species of birds know how to produce food ("crop milk") for their young: they produce food for their young when they have young. This can be triggered by visual clues (e.g., the open beak of bird young), or by the smell (aka "pheromones") of the young, or by other species-specific cue. $\endgroup$
    – AlexP
    Commented Jan 22, 2018 at 1:08
  • $\begingroup$ This seems like a question about real world biology not about building a fictional world. $\endgroup$
    – sphennings
    Commented Jan 22, 2018 at 3:10
  • $\begingroup$ If you know the platypus does it, then surely you researched the platypus prior to asking this question? Since I don't see evidence of that research (which is likely to provide the answer you're looking for), downvoting. $\endgroup$
    – Frostfyre
    Commented Jan 22, 2018 at 13:14
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    $\begingroup$ I did do some research on the platypus, but I could not find anything about when they knew to start creating milk, only that they 'sweat' milk through the skin on their stomach, which gathers in ridges found there. $\endgroup$
    – Rasul
    Commented Jan 23, 2018 at 0:52

3 Answers 3


It could be something as simple as the sucking on the tit that causes milk production to begin. In humans and other mammals, the interaction and regulation of milk production is a fairly complex system, but it doesn't have to be for your species. The body is primed by the laying of the egg, and N days later, the body prepares a small amount of milk. If that isn't consumed, it is reabsorbed by the body. That process repeats until one day, the small amount of milk gets drunk by a little one sucking it out. At that point, the body goes into full milk production and maintains it either as long as it keeps getting drunk or for a fixed number of days, depending upon the weaning mechanisms of your species.

Let me repeat -- this is a way simpler model than anything in mammals, and if you write a story with such breastfeeding, you better make sure you highlight that it is alien biology or you'll be rightly lambasted for not getting your science right!



Progesterone is a sex hormone that is important in regulating various parts of the female reproductive system, particularly in timing the menstrual cycle and pregnancy. When progesterone is high during pregnancy, the alveolar mammary glands glands are inhibited in their milk production. After birth, progesterone levels drop rapidly, and lactation is triggered. Prolactin is a different hormone that causes mammary glands to swell. Its effects are mitigated by progesterone, until birth, whereupon milk production begins.

Honestly, I'm doing you a disservice trying to describe hormonal interactions that go into breastfeeding in a few sentances. Hormone production and interaction is very complicated, far more than I know about. But ultimately, this is the mechanism that will cause a (female) mammal to lactate after birth. Adopt and adjust as necessary for your aliens. Or don't even mention it; it can just be assumed that any other creature has the hormones needed to manage their biological systems.


You might have it based on cues from the egg itself.

When people want to see if a chicken egg is alive and near hatching there are three things they'll try. Tapping on the egg shell and listening for a tiny noise in response or even a slight vibration; placing the egg against their cheek to see how hot it is; and shining a bright light on it to see if their are veins.

Making these tricks a bit stronger and occurring a few days before it's ready to hatch would work nicely. Hearing the egg chirping, actually rolling a little, growing hotter, or having veins or some visual cue on the egg shell, would be the signal for the mother to start lactating.

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    $\begingroup$ The aliens might eat the shell to reclaim some of the calcium that went into it and the eggshell could be full of hormones that kickstart lactation. The only problem is the temptation to eat the delicious shell before the young hatch, which I understand can be problematic for chickens. $\endgroup$
    – Willk
    Commented Jan 22, 2018 at 14:24

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