I am looking at anise swallowtail larvae squirming in their eggs, getting ready to hatch.
What happens to embryos’ waste products for species that develop in self-contained eggs? Is this process the same across insects and other invertebrates, amphibians, reptiles, and birds?
And at least for butterflies, my understanding is they eat their egg after hatching. This means they would be eating any waste products that were generating while they developed. How are they not harmed by this?
That title had me concerned for a few seconds. I thought you had loads of non-mammalian embryos lying around somewhere which you wanted to get rid of. Haha
Good question though! This website very briefly explains waste removal inside a bird egg. Basically the egg has a “garbage sack”, called allantois which holds liquid waste. Gaseous waste can get through the shell.
I do not know how it works for insects, however.
Same here! 
i have no idea what invertebrates do, but for vertebrates, read up on the allantois and the difference between amniotes and anamniotes.
I wonder if the waste products would be significant with an animal so small with a relatively quick digestion period. Animals defecate to rid themselves of unnecessary fibers, old cells, etc, and I doubt that there is much fiber in a caterpillar’s egg. Much of their frass after hatching appears to be mostly unneeded, semi-digested plant fiber, so maybe waste just isn’t much of a problem for leps. This is just speculation, I think someone would have to use a powerful microscope for a better answer.
A lot of animals eat their own waste products. They are probably fine with the waste products from developing in the egg, but again, this is just a guess.
As pisum pointed out, the allantois is key here for amniotic tetrapods (so evolutionarily, everything after amphibians). In essence, the allantois is a membrane that has an outpocket into which the toxic nitrogenous waste can be shunted and sequestered. For those things that retain their shell, this is just another membrane underneath the shell. The shell is gas- and water-permeable, so oxygen and water can get in, and the carbon dioxide waste can get out. However, the nitrogenous molecules produced during embryogenesis are too big, so are just set aside in a place they won’t damage the embryo directly. For amphibians, I think it just diffuses across the gelatinous membranes surrounding the egg, though the egg phase is so quick for many amphibians, they may not even have to do that.
Beyond just embryonic waste removal, some taxa have evolved strategies utilizing the nitrogenous waste. For example, sharks retain some in their tissue to fine-tune osmotic (water) balance. Some butterflies sequester it in their tissue and use it to create white colors, such as what the Cabbage White does, though I’m not sure this happens in the egg phase.
Fascinating! Thank you, everyone for sharing your insights :)
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