How do varroa mites affect honeybee colonies?

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Varroa mites attach to honeybees and feed on both brood and adult bees. They spread to other colonies through “drifter bees” and human actions. They are known to transmit viruses such as deformed wing virus, which can cause malformations and weaken bees, and they are associated with colony collapse disorder, in which the adult workers of a bee colony suddenly die.