It struck me that the connection between the spies punishment and the discussion in Masechta Sota also can be given as an analogy to the crime of the Sotah. It appears as if the actual punishment appears to be almost the same as the actual punishment of a guilty Sotah after she drinks the water. Note also that the man was punished in the same way as the Sotah.
Just as the Sotah has sinned by adultery (even after having been warned) and that the punishment is through the organs by which she sinned as well as showing the destruction of the future life, so to the meraglim were punished through the organ by which they sinned and the destruction of the future life that they could have created.
Art Scroll Sotah Daf 35a3 note 27 cites Maharal (Chidushei Aggada) that the navel is the place from which life begins (Sotah daf 45b). The tongue is the organ that sets Adam apart from all other creatures in this world (as a medaber). Thus, it is the completion of humanity, while maggots are a symbol of corruption and decay. Just as the meraglim used the final part of their being, to destroy their complete existence, so to did the tongue reach to the beginning of their existence to show that they had become completely corrupt.
Ben Yehoyada connects the navel to Eretz Yisrael (Sanhedrin 37a) as the navel of the world.
They sinned with their tongues, i.e. by speaking slander; therefore,
their punishment came via their tongues (Rashi to the verse;
Maharal (Chidushei Aggados) explains why this unusual punishment was appropriate for the spies. The navel is the place from which life
begins (see below, 45b). The tongue, as the organ of speech, sets Man
apart from other creatures; it thus represents the completion of
Man. Maggots represent corruption and decay. The stretching of the
tongue to the navel, and the passage of maggots between them,
signified that the corruption of the spies encompassed them fully.
They had become completely evil, from beginning to end, root and
branch (see there for two other explanations; see also Gur Aryeh to
Alternatively, since Eretz Yisrael, is considered the center, or
navel of the world (see Sanhedrin 37a), it is fitting that those who spoke against Eretz Yisrael be punished via their navels (Ben