Be quiet to get close to feeding Silver Ys

A still, balmy night, there are many Silver Y moths feeding on the garden flowers: lavender, perennial peas and buddleia. I always have trouble taking photos of the Silver Ys, they are so flighty! A step forward and they all disperse. A typical shot when I am outside is like the one above. My best shots have always been from behind the conservatory window. Today I understood why. If found out that you want to get close to these moths you need to be quiet. Why did this surprise me? I knew moths are able to hear bat ultrasounds and respond with erratic flight and even dropping to the ground, I even wrote a post about it. But there is nothing like first hand experience for learning. I tried to take shots from the cloud of silver Ys feeding in the buddleia tonight, they were visible in the dusk light as hovering silouettes by the profile of the large flowers. And then, as I approached, camera pointing up and triying to decide which one to shoot, I stepped on a crunchy leave inadvertently. The whole cloud of moths responded instantly by flying in different directions: of course they can hear! Many sounds we make while moving about are actually ultrasounds (click your fingers near a bat detector to test this). I bet walking on my pebbly path does this too, and this was what was keeping them away. I moved slowly, placing each foot carefully and slowly on the ground. Stood next to the buddleia and waited until the silver Ys came back and resumed their feeding. And this time managed some outdoor clear shots.

Moth bat detectors and the evolution of butterflies

This noctuid moth, a male Large Yellow Underwing, Noctua pronuba entered the house a couple of nights ago and my cat alerted me to it. This is a large moth, very variable in colour: females are lighter than males, and both sexes have a black mark near the end of the wing. As most moths, they have a highly developed sense of hearing and can hear ultrasounds by means of a timpanal ear behind their middle legs, in order to detect and avoid echolocating bats. When they detect an incoming bat, moths carry out unpredictable flight maneuvers: suddenly flying up, carrying our loops or power diving or dropping with closed wings. Large Yellow Underwings also suddenly drop to the ground when they are flushed during the day. Their coloration is cryptic and they blend well with the leaf litter, so once they fall to the ground they are hard to spot.
Avoidance of echolocating bats is thought to have been the selective pressure underlying the repeated evolution of bat detecting tympanal ears in moths. This happened repeatedly involving different anatomical regions in various moth families more than 50 million years ago. Surprisingly, the evolution of diurnal butterflies from their nocturnal moth ancestors appeared to have occurred at the same time: day flying and the subsequent radiation of butterflies resulted from a bat avoiding strategy.

More information
Yack JE, & Fullard JH (2000). Ultrasonic hearing in nocturnal butterflies. Nature, 403 (6767), 265-6 PMID: 10659835