The cup furnishes a thin film like swan-skin which imbibes the sapid exudations from the stem, the source of nourishment.

I have seen a young grub, hatched under my eyes, eat as his first mouthfuls this tender cottony layer, which is moist and flavoured with tannin.
Such nutriment, juicy and easy of digestion, like all nascent organic matter, is only found in this particular spot; and it is only there, between the cup and the base of the cotyledons, that the elephant-beetle establishes her egg.

The insect knows to a nicety the position of the portions best adapted to the feeble stomach of the newly hatched larva.
Above this is the tougher nutriment of the cotyledons.

Refreshed by its first meal, the grub proceeds to attack this; not directly, but in the tunnel bored by the mother, which is littered with tiny crumbs and half-masticated shavings.

With this light mealy diet the strength of the grub increases, and it then plunges directly into the substance of the acorn.
These data explain the tactics of the gravid mother.