How do animals know when it's time to mate and reproduce as soon as spring arrives? Researchers from Nagoya University in Japan published a report in the British journal *Nature* on the 20th, indicating that the thyroid-stimulating hormone (TSH) in certain animals increases in secretion as the daylight hours begin to lengthen. This simultaneously stimulates the brain to send the message that "spring has arrived." Therefore, TSH can also be considered the "spring messenger hormone" in living organisms.