Mealybugs only eat plant sap, but sap doesn't contain all the essential amino acids the insects need to survive. Luckily, the bugs have a symbiotic relationship with two species of bacteria -- one living inside the other in a situation unique to known biology -- to manufacture the nutrients sap doesn't provide.
The net result: The bacteria get a comfy mealybug home, and the bugs get the nutrition they need to live.
University of Montana microbiologist John McCutcheon describes such mutually beneficial relationships used to solve life's little problems as "almost hilariously complicated. But animal-bacterial relationships are extremely common in nature, and it's my goal in life to help people understand that it's normal."
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