The air imprisoned in the bubbles of the surrounding froth accounts for the phenomenon.

Extremely refractory to heat, it had absorbed the heat of the oven and had prevented it from reaching the frozen substance in the centre of the omelette.
Now, what does the Mantis do?
Precisely what Rumford did; she whips her albumen to obtain a soufflee, a froth composed of myriads of tiny air-bubbles, which will protect the germs of life contained in the central core.

It is true that her aim is reversed; the coagulated foam of the nest is a safeguard against cold, not against heat, but what will afford protection from the one will afford protection from the other; so that Rumford, had he wished, might equally well have maintained a hot body at a high temperature in a refrigerator.
Rumford understood the athermic properties of a blanket of air-cells, thanks to the accumulated knowledge of his predecessors and his own studies and experiments.

How is it that the Mantis, for who knows how many ages, has been able to outstrip our physicists in this problem in calorics?
How did she learn to surround her eggs with this mass of solidifying froth, so that it was able, although fixed to a bough or a stone without other shelter, to brave with impunity the rigours of winter?
The other Mantes found in my neighbourhood, which are the only species of which I can speak with full knowledge, employ or omit the envelope of solidifying froth accordingly as the eggs are or are not intended to survive the winter.

The little Grey Mantis (_Ameles decolor_), which differs so widely from the Praying Mantis in that the wings of the female are almost completely absent, builds a nest hardly as large as a cherry-stone, and covers it skilfully with a porous rind.