Aelian (Claudius Aelianus), On the Nature of Animals, 16, 27 (= BNJ 86F 21b)
“Agatharkhides claims that there is a group of people in Libya–and that they are also called the Psylli–in most ways they aren’t really different from the rest of humankind in their lifestyle except that their body has a strange and incredible quality that sets them apart. You see, creatures that sting as part of attacking don’t harm these people at all!
Indeed, they don’t even notice a snakebite or a spider-bite that might be fatal to other people, nor even a scorpion’s sting. When one of the creatures gets near them and touches them, it acts like it has taken some sleep-causing drug as soon as it smells them! They contract a kind of drowsiness or drugged state and become weak and slow until the person walks away.
Also, when they want to test whether their babies are trueborn or bastards, they leave them in the middle of snakes just as I said above, the way gold-workers test metal in fire.”
Diogenes Laerius, Lives of the Philosophers 5.6 [Heraclides 89-90]
“He seems to have freed his country from tyranny by killing the monarch, as Demetrius of Magnesia claims in his People with the Same Names. Demetrius also tells this next story about him.
From the time he was a child he raised a pet snake. When he was near death he told one of the people he trusted to hide his body but to put the snake on his funeral litter so that he might seem to have transitioned to a place among the gods.
They did this, but while the people were taking Heracleides in his procession and were shouting out, the snake heard it and came out of the shroud, troubling people. Once everything was uncovered, Heracleides was known as he truly was, not as he seemed to be.”
“A type of Egyptian frog is a bit of a wise creature and for this reason it surpasses other frogs by a lot. If it this frog runs into a water snake that lives in the Nile, it bites off a shoot of reed and carries it forward obliquely and holds it tight, and it will not let it go until its strength gives out. The snake cannot eat the frog with the reed, since its mouth will not open as wide as the reed would demand. From this trick, the frogs surpass the strength of the watersnake with wisdom”