EPOW - Ecology Picture of the Week

Insect Ghost Trails

Unidentified moth

Explanation:  What ghostly image is this?  

It is the dead of night in a darkened cabin deep in the woods.  All lights are off except for the one on my camera.  I am shooting a video, and only later, while reviewing the sequence, do I see this bizarre manifestation.  

But this is no spirit.  It is an insect in flight, a single moth.  

The frame rate on my camera has a long enough shutter speed such that each frame captures several wing-beats of the moth, appearing like a ghostly apparition with multiple spikes.  What I did in these images is to stack several adjacent frames to produce these long, bizarre trailing figures.  The main image, above, for example, consists of four frames knit together; you can see three small breaks in the insect's flight path where the electronic shutter snapped to the next frame.  

Here are a few more examples.  Click for fuller-size images, and see if you can spot those breaks in the trails where one camera video frame ends another begins.  
    

Knowing the frame rate of the camera -- in this case, the camera is a Panasonic DMC-SZ7 pocket digital camera, set to HD video mode at 30 frames per second (fsp) -- you can calculate the wing beat rate of the moth.  Each frame (each segment of the "ghost trail") contains 4 or 5 wing beats; let's average it to 4.5 wing beats per frame.  If each frame is 1/30 second, this converts to [4.5 wing beats] / [1/30 sec]  =  135 wing beats per second.  

In comparison, hummingbirds range from 12 to maybe 100 wing beats per second.  Moths have them beat, so to speak! 

In another study (Snelling 2012), the wing beat frequency of an adult locust Locusta migratoria was found to average only 23.7 beats per second, a veritable slow-poke compared to these cabin moths.  In one summary, depending on the species, butterflies beat their wings as slowly as 2-3 beats per second or up to about 20 beats per second, slo-mo compared to these zipping moths.    

Finally, check out these crazy trails:
 

Information:
     Snelling, E.P., R.S. Seymour, P.G. Matthews, and C.R. White.  2012.  Maximum metabolic rate, relative lift, wingbeat frequency and stroke amplitude during tethered flight in the adult locust Locusta migratoria.  Journal of Experimental Biology 215[Pt 18]:3317-3323.