Sunday, March 22, 2015

Beam Me Up, Scotty!

I have discovered that my pair of floodlights, beaming light in the direction of my backyard hives, can be very enticing to bees on those warm summer nights when bees cluster on the outside of the hive late into the evening. Within minutes several bees were buzzing and spiraling around the lights. Some species of bees, including the Asian honeybee Apis Dorsata, have evolved  pre-dawn, dusk, or nocturnal foraging abilities, perhaps as a result of competitive or predation pressures (DOI: 10.1111/j.1095-8312.2004.00399.x), and seemingly in spite of the physiology of their eyes (10.1098/rspb.1996.0222). I am not aware of such behavior in the Western honeybee Apis Mellifera. Were the bees tempted by a particularly bright "moon"? Did they mistake the light source for the sun? I wonder how they processed the emergence of a twin moon, or sun as the case may be. Whatever the cause, it was an unexpected event! On a side note, did you know that while the Asian honeybee requires the light of the moon for navigation at night, they do not reference the position of the moon in their dances? Instead they apparently reference the sun's position below the horizon. (DOI: 10.1016/S0003-3472(85)80009-9). Wowza! Is that similar to how we find the fridge in the middle of the night?

Bees navigate in part by the angle of the sun in relation to their direction of travel. Here is an explanation of how these angles factor into the "bee-havior" of insects spiraling around lights at night: Article by mathematics Prof Khristo N. Boyadzhiev of Ohio Northern University. Originally published in the The College Mathematics Journal, Vol. 30, No. 1. (Jan., 1999), pp. 23-31. I deleted the formulas but kept relevant illustrations while citing it. If formulas are your thing, check out the full article at (Free registration required, which may have changed since I last accessed it.)

"Everybody has seen how moths spiral around a night light. If they are simply attracted to the light, they would fly on a straight line. The spiral trajectory is explained by the way some primitive animals orient themselves by a point light source. Insects have compound eyes consisting of many ornmatidia, which are single detectors of light. Beams of light stimulate a small group of ommatidia, orthogonal to the beams, and this determines the angular position relative to the light source. When the beams are parallel and the insect wants to go in straight line, it needs to fly in such a way that the same group of ommatidia will stay activated. That is, it needs to keep a constant angle with the beams, see Figure 1.

For millions of years insects used the moon and the sun for orientation. Their beams are practically parallel and help maintain a straight path. The situation changed when humans introduced other light sources. If a moth keeps a constant angle a to the radial beams of an electric light, then it flies on a straight line only when flying directly towards the light, or flying directly away from the light. It will approach the light on a spiral or fly away on a spiral. In the special case it flies in circles around the light. When the motion is in a plane, the trajectory is an equiangular spiral, as confirmed by observations.

I don't know about you, but my brain hurts and I am feeling dizzy. I was tempted to conduct an experiment testing this formula, but I would only burn myself, fall off the step-stool, and see bright spots for days!


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