Viper
The viper that fastens onto Paul's hand symbolizes danger and the presence of evil, yet also serves as a testament to God's protection and power over harm.
This incident highlights God's sovereignty and protection over His servants, demonstrating that no harm can befall them without His permission. It also serves as a sign to the islanders of God's power.
In ancient cultures, snakes were often seen as symbols of evil or danger, and surviving a snake bite was considered miraculous.