Passage 9.28.3
τούτου μὲν τοιαῦτα ἤκουσα· ἐν δὲ τῇ χώρᾳ τῇ Ἀράβων ὅσοι τῶν ἔχεων περὶ τὰ δένδρα τὰ πάλσαμα οἰκοῦσι, τοιάδε ἄλλα ἐς αὐτοὺς συμβαίνοντα οἶδα. μέγεθος μὲν κατὰ μυρσίνης θάμνον τὰ πάλσαμά ἐστι, φύλλα δὲ αὐτοῖς κατὰ τὴν πόαν τὸ σάμψουχον· ἔχεων δὲ τῶν ἐν τῇ Ἀραβίᾳ κατὰ ποσοὺς καὶ πλείονες καὶ ἐλάσσονες ὑπὸ ἕκαστον αὐλίζονται δένδρον· τροφὴ γὰρ αὐτοῖς ὁ τῶν παλσάμων ἐστὶν ὀπὸς ἡδίστη, καὶ ἔτι καὶ ἄλλως τῇ σκιᾷ τῶν φυτῶν χαίρουσιν.
Such things I have heard about this matter. As for the land of the Arabs, I know the following additional facts concerning the snakes that dwell around the balsam-trees there. The balsam-trees are about the size of a myrtle bush, and their leaves resemble the herb called sampsuchon. Beneath each tree in Arabia dwell snakes, sometimes fewer and sometimes greater in number, for their most delightful nourishment is the sap of the balsam-trees, and they also find pleasure in resting in their shade.