In a colony of tree wasps, workers on nursemaid duty crawl this way and that along the bottom of their nest, tending the youngsters in the comb. Most of the workers dutifully look after the queen's offspring, stopping only to spit a runny meal into the mouth of a pale, lumpy larva snug in its cell. But one of these workers is up to no good. This selfish worker stays still for a minute or two in a suspiciously crouched position. She's laying her own egg in an empty cell.
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