which is the most powerful biological weapon ever?

Please clarify.

Do you mean a weapon in the "biological warfare" sense ... a weapon developed for killing other humans such as gas, radiation, or infecting them with some biological disease?

Or a "weapon" that humans have used against other species (like insecticides or antibiotics)?

Or a "weapon" in the metaphorical sense as something used by other species for killing prey or defending against predators (like venom or echolocation)?

Or a "weapon" in the metaphorical sense of a strategy for survival and reproduction (like the sheer ability of bacteria to mass-produce)?

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>"Microbes used as weapon in modern warfare ??"

Thanks. So you mean the first of my choices.

In that case I would say smallpox.

Not because it is the most virulent disease that has existed ... while extremely virulent, there are others probably worse.

... But smallpox has actually been used as a biological weapon:

http://www.bbc.co.uk/history/worldwars/coldwar/pox...

"At the time of the Pontiac rebellion in 1763, Sir Jeffrey Amherst, the Commander-in-Chief of the British forces in North America, wrote to Colonel Henry Bouquet: 'Could it not be contrived to send smallpox among these disaffected tribes of Indians? We must use every stratagem in our power to reduce them.' The colonel replied: 'I will try to inoculate the [Native American tribe] with some blankets that may fall in their hands, and take care not to get the disease myself.' Smallpox decimated the Native Americans, who had never been exposed to the disease before and had no immunity."

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birth control