By Dave DeGroot, Cohort 2
Dozens of species of sphinx moths – some of the largest moths in the world – work the “night shift” during Pima County’s monsoon season. Unfurling their long proboscises, they zero in on the nectar offered by pale flowers such as sacred thornapple Datura, Jimson weed, evening primrose, honeysuckle, different kinds of phlox, penstemons, and other desert plants that are somewhat visible in the dark.
The big moths’ nighttime flights take a lot of fuel. Their bodies are relatively large and they stay airborne for long periods of time. They have a way of hovering at flowers like hummingbirds, a skill that is very useful for drinkingnectar but burns up calories.
On cool nights they have a little trouble. When their body temperatures drop below 96 degrees F., they cannot fly efficiently. Daytime insects utilize higher ambient temperatures and the sun’s warming rays to stay active, but the nocturnal sphinx moths need another strategy.
Not to worry. The sphinx flyers have developed a way toraise their body temperature to achieve the necessary 96 degrees F. They vibrate. They use wing muscles in a kind of quivering behavior that raises the temperature of their thorax. They sit on a perch and vibrate to prepare for take-off, something like an airplane warming up on a runway.
Ethan Fraijo and I witnessed this behavior during a nocturnal foray into the Tortolita Preserve in September. Our goal was to obtain moth photos. Our method was to hang up a white bedsheet and mount an ultraviolet light next to it. Sphinx moths would often be among the first visitors to our outpost. One sphinx crashed into our bedsheet with an audible “smack.” Not much finesse – we thought it was having trouble with a low body temperature. So we decided to give it a hand.
The moth seemed to feel secure in the palm of Ethan’s hand and began to quiver. In just a couple of minutes it spread its wings and took off. Interestingly, it hovered around our ultraviolet light for only a short time before flying away. Other sphinx moth visitors came and went. Meanwhile dozens of tiny moths remained enthralled by our UV light. The big guys, however, sized up our outpost quickly and departed. They weren’t about to waste precious body heat hovering around a nectarless lightbulb. They had things to do and places to go – while their temperature gauges registered 96 degrees.