I am also curious as to why you must freeze them for 24 hours and what certain methods for euthenizing are considered most human and why. I always feel torn up doing it.
I recommend 24 hours (at least) based from my very first experience euthanizing a mantid in the freezer. When I removed the mantid after 10-12 hours in the freezer, it warmed up after several minutes at room temperature, and it sprang back to life in obvious discomfort/pain.
I found 24 hours freezes solid the liquids/tissue in any mantids I had to euthanize (tested in my bug fridge freezer, the kitchen fridge freezer, and a chest deep freezer); although, I tend to leave them in the freezer for 2 to 3 days to ensure the poor creature was properly euthanized.
The freezer is the only method considered humane, as the mantid slows down (bodily functions/metabolism/alertness/awareness/etc) due to the cold and looses total consciousness before dying. Other methods involve some degree of discomfort/pain (
read about mantid pain here), or even viewed as torture and/or cruel especially to the keeper who does it, so are not humane to either.
The only variation I have heard on humane euthanasia is to place the mantid into a refrigerator for 24 hours first. The fridge cools off the mantid, slowing down it's bodily functions considerably, and said to ease the transition of the mantid from it's warm environment to the freezer. At which point it is then placed into the freezer for 24-48 hours to finish the process.
Personally I still detest euthanizing too, but in the end it is a unfortunate part of life no matter the species/creature involved - the discomfort/pain and suffering reaches a point that it outweighs the euthanasia process.
