And we're worried about zebra mussels?

TOA BAJA, Puerto Rico — When hordes of monkeys began invading Puerto Rico's agricultural fields, devastating crops and eluding capture, the major concern was trapping them before they reached urban areas, where they would pose a public health hazard and be nearly impossible to round up.

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The animals — descendants of the patas and rhesus monkeys that escaped from medical-research labs — are known to be fertile and aggressive.

Mature monkeys can weigh up to 50 pounds, and it's estimated the monkey population in southeast Puerto Rico stands at between 1,000 and 2,000 — and it's growing every day.