Black hole

The "Black Hole" mosquito trap that attracted so much of Dah's mirth ("What you pay for that thing?") turned out to be a fine thing after all.



Jack's morning job was to empty the trap, which had hummed away the night on the floor of the bedroom. He was very Buddhist about it, sealing and placing the trap outside on the deck. Many of the mosquitos seemed to expire or go to sleep on the floor of the trap, with their feet sticking up. The several selected by destiny or will continued to fly around the trap batting themselves against the screen walls. When the number of "actives" had fallen to a countable number Jack opened the trap. The actives flew away (Dah suspected back to the bedroom) and the rest Jack dumped onto the deck for a count (some of these had been bluffing and flew away too.)

Jack made a graph of the count, combined with some weather data.




Question: What is the cause of the dramatic increase in January?