Packages piled up, blocking the aisles and the heavy sorting machinery. Boxes of steaks, fruit and other perishables rotted. Rats dashed across the floor. At one point, Scantlebury said, the “whole building was filled with gnats.”

The delays were particularly tragic for live animals, including baby chickens and crickets, that are transported through the U.S. Postal Service. Usually, mail handlers say, they can hear the birds peeping and rustling around in their boxes.

This month, one worker said, she found a box with air holes in a pile of packages. Instead of hearing the gentle sounds of baby chicks, she heard nothing.

Workers sometimes see shipments of crickets jumping around inside t