‘And when the barbarians saw the venomous creature hanging from his hand, they said one to another, “No doubt this man is a murderer, whom, though he has escaped from the sea, yet Justice (dike) has not allowed to live.” '
It was of a type known to the islanders to be venomous, and the barbarian inhabitants of the island looked meaningfully at one another, and said that he must be a murderer who, even though he had escaped the sea, Justice (dike) would not allow to live. It would appear that the Maltese venerated the Greek god Dike.
There seems little doubt that Luke sees this incident as symbolic. To all Christians the snake represented Satan, and here was his representative seeking to destroy Paul, but failing (as he had in the storm). As Jesus Himself had said, ‘Behold, I give you power to tread on serpents and scorpions, and over all the power of the enemy, and nothing shall by any means hurt you' (Luke 10:19). The Enemy had once again attacked, and had failed. Thus was indicated that the conqueror of Satan was on his way to Rome, to turn them from darkness to light, and from the power of Satan to God (Acts 26:18), and Satan was powerless to do anything about it.
Today there are no venomous snakes on the island of Malta, but that is no evidence that there were none in those days, for as men became more sophisticated they would seek to exterminate them and that would not be difficult on so small an island. Locals do not make mistakes about which snakes are poisonous.