Because in 30bc she heard of the disaster at the t=battle field she thought all was lost so she commited suicide
Cleopatra VII let a snake bit her because her husband, Antony, stabbed himself
She had already made up her mind to commit suicide, and death by venomous snakebite was apparently her choice of doing so. The old accounts, and William Shakespear's play, state that the snake was an "Asp", which is a small viper native to Egypt, also called a Horned Viper. However, it's unlikely that this was the actual snake that she allowed to bite her, since death from a bite from one of these snakes would be a very long, slow, and excruciatingly painful process, IF you died at all. A person would be more likely to simply lose a limb to the necrotic effects of the venom. If it's true that Cleopatra committed suicide by snake bite, she most likely would have chosen the Egyptian Cobra. Cobra venom attacks the central nervous system, often producing a euphoric state, or "high", prior to unconciousness, coma and death from asphyxiation(suffocation)as the venom shuts down the automatic breathing reflex, so it would have been a relatively painless death.