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SCV Outdoor Report: Phototaxis

1-scvoutdoorreport-logoBy Wendy Langahns:

Hot August nights - a fine time to relax in a rocking chair on the front porch and listen to the crickets chirp.  Especially if you’re a cat.  Our cat, Mr. Bucky, likes it so much that he’s taken to sitting at the front door and yowling until I take him outside for a “rocking good time.”

He especially enjoys watching the moths as they flutter around the porch light.  And now that I’ve installed a small reading lamp, he’s even more facinated.  All this raises a couple of interesting questions - why ARE moths attracted to light?  And are certain wavelenghs of light more attractive than others?

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Bug researchers (entomologists) refer to the automatic movement towards or away from light as “phototaxis”.  Many species of moths exhibit postive phototaxis; they move towards the light.  Mr. Bucky also moves towards the light, (or at least he would if if I weren’t holding on to him).  Technically though, I would describe his behavior as positive “bug-taxis”, rather than phototaxis.

But back to the bugs - entomologists have come up with several possible reasons why moths exhibit positive phototaxis.

1)   Flight orientation.  In other words, light tells them which way is up?


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2)   Reference point.  Using the moon to calibrate their flight path.  This would be especially useful for migrating moths.

3)   Escape route.  Flying up (towards the light) may be safer than flying down (away from the light), especially if you’re trying to escape from a predator.  Of course, if you’re being hunted by a bat, this strategy wouldn’t work so well.

But are certain wavelengths of light more attractive than others?  We know that insects (including moths) can see UV light (shorter wavelenghs of light.  Recently, researchers in the Netherlands (which is the global HQ of the electronics company Royal Philips Electronics) tested six different types of light bulbs, each emmitting different wavelengths of light, to determine which wavelenths attracted moths.  They found that “moths are most attracted to shorter light wavelengths—those near the ultraviolet and violet portions of the light spectrum” (wavelength of less than 420 nm).  Not only that, but they found that the larger moths were more attracted to those wavelengths than smaller ones.

This findings could have implications for the types of outdoor lighting we use, especially in those areas near open spaces.  Using lightbulbs with longer wavelenths could reduce the effects of “light pollution” and increase the number of larger moths.  This could have a positive effect for the birds, who eat the moth caterpillars, and on the pollination of night blooming plants.

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I took a trip over to the hardware store and found a replacement lightbulb for my reading lamp.  Let’s see how the bugs react to it.  If it works, poor Mr. Bucky will just have to make do with listening to the crickets.

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Upcoming Outdoor Events:

Saturday, August 13th, 7:30 - 9:30 PM, Full Moon Hike at Towsley Canyon.  Follow that adventurer’s spirit and step into the night on the ruggedly beautiful Wiley Canyon Trail. Look and listen for wildlife in the light of a summer full moon on this moderate hike. Meet at Towsley Canyon’s front parking lot. Easy walk, 2 hours. Meet at Towsley Canyon’s front parking lot.  For directions and trail maps, click here.

Saturday, August 20th, 8:00 - 10:00 AM, Early Morning Bird Hike at Towsley Canyon.  We think of summer as being a cushy time for animals.  But for our local bird residents, it’s a challenging time, with soaring heat, little water, and vegetation displaying all the signs of stress.  Join us to see who the tough ones are.  Beginning birders are welcome.  Binoculars optional.  Easy walk, 2 hours. Meet at Towsley Canyon’s front parking lot.  For directions and trail maps, click here.

Trail Maintenance Schedule.  Come join our volunteers as they help maintain our trails.  Contact Steve at machiamist@aol.com for time and place.

Wednesday mornings, August 3, 10, 17, 24, & 31.

Saturday mornings, August 13 & 27.

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You can listen to stories like this every Friday morning at 7:10 a.m. on "The SCV Outdoor Report", brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.

For the complete MRCA hike and activity schedule and for trail maps, click here or go to www.LAMountains.com.

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