I never see her explore the tube or take its size.

She stands on the trellised orifice; and there the matter ends.

Can she be apprised of the depth of the chasm by the comparative faintness of the offensive odours that arise from it?
Can the sense of smell measure the distance and judge whether it be acceptable or not?
Perhaps.
The fact remains that, despite the attraction of the scent, the Flesh-fly does not expose her worms to disproportionate falls.

Can she know beforehand that, when the chrysalids break, her winged family, knocking with a sudden flight against the sides of a tall chimney, will be unable to get out?
This foresight would be in agreement with the rules which order maternal instinct according to future needs.
But, when the fall does not exceed a certain depth, the budding worms of the Flesh-fly are dropped without a qualm, as all our experiments show.

This principle has a practical application which is not without its value in matters of domestic economy.