Stupid Question ™
July 26, 2001
By John Ruch
© 2001
Q: Why are bugs attracted to bright lights? And why only at night? Why do yellow lights deter them?
—Steven Barger
A: It is presumed that nocturnal moths and beetles mistake bright artificial lights for the Moon, which they probably use as an orientation device while flying at night.
Day insects aren’t fooled because there are very few artificial lights as bright as the Sun (and there are many other visual cues in daylight).
Yellow, orange and red lights (including sodium-vapor street lamps) are essentially invisible to most insects, which can’t see into the red portion of the spectrum.
Insects do see blue and ultraviolet light very well, including those wavelengths in moonlight. Candle flames and campfires contain weak amounts of these wavelengths, and have attracted insects in small numbers since ancient times. However, the common modern light bulb, and especially the mercury-vapor bulb, put out lots of UV and can attract huge numbers of insects.
The Moon theory says that moths know that the brightest light at night—the Moon—is always “up.” But if they mistake a street lamp for the Moon, they find themselves in the utterly confusing position of flying above or past the “Moon.” They can no longer navigate. Also, the brightness of the light at close quarters makes them think it’s daytime, so they go to sleep.
This theory is not airtight, but the evidence is strong. Lights attract insects best on cloudy nights (when there’s no real Moon) and worst on clear, moonlit nights. Also, lights attract mostly migratory species, or males that are traveling to find mates.
Similarly, night-migrating birds have been thrown off course by artificial lights on cloudy or moonless nights.
There’s experimental evidence that moths fly in a straight line by keeping themselves at a regular angle from the Moon, using it as a reference point. Some moths maintain this same angle from artificial lights before spiraling into them. This spiral could be the result of the confused moth trying to maintain the proper angle as it flies past or above the “Moon.” (Some dive straight into the light, which could be the result of an overflying moth thinking it’s upside down, and diving to keep the “Moon” above it.)
More evidence comes from the surprisingly short range of attraction.
The 125-watt mercury-vapor bulb used in insect-collecting traps has the same brightness as the Moon at a distance of 115 to 1,703 feet (depending on the phase of the Moon you compare it to). But a mercury street lamp 30 feet high will attract insects from only 33 to 56 feet away. Why? The standard mercury bulb has the same apparent size as the Moon at a distance of 43.5 feet—right in the middle of the attraction range. It’s the right brightness and the right size—a perfect fake.
However, the same bulb placed 2 feet off the ground will attract moths from only about 10 feet away. It’s got the right brightness and size, but the wrong elevation, and fools relatively few moths.
Showing posts with label insects. Show all posts
Showing posts with label insects. Show all posts
March 28, 2008
March 27, 2008
Dead Roaches On Backs
Stupid Question ™
Aug. 19, 1999
By John Ruch
© 1999
Q: Why do roaches always die on their backs?
—Dumb and Dumber
A: There are a lot of people with opinions on cockroach death positions, but as far as I can tell, none of them have specifically studied the matter.
So be warned that the following answer is really just an educated guess that will hopefully one day be tested by some grad student, perhaps in his or her undoubtedly cockroach-ridden campus apartment.
The most important observation, from entomologists and pet store owners, is that cockroaches do not always die on their backs. Sometimes they die very much upright.
So I think our question actually is: why are roaches usually found dead on their backs? It’s a subtle but important difference.
Many insects tend to topple onto their backs when incapacitated, especially those with a flat back and legs positioned directly under the body. Flies are the classic example.
Roaches have a similar design, but a lower center of gravity. They probably need a stronger force than gravity to topple them over. Dehydration may be the destabilizing factor.
Insects are extremely susceptible to dehydration. Shortly after death, their legs dry and curl up. This makes toppling over almost inevitable. Ohio State University entomology associate Kyle Jordan said this is a common problem when mounting insects for display: “They’re very difficult to get to stand up. They’re unstable.”
Roaches in the home are usually found on smooth surfaces in the bathroom or kitchen. While a healthy roach is pretty good at righting itself, the smooth surfaces no doubt aid a sick or dead roach in toppling over.
If you know roaches are in your home, you’re probably also trying to poison them. Many off-the-shelf insecticides are neurotoxins that cause spasms and uncoordination. Between those two symptoms, roaches commonly fall onto their backs and are unable to right themselves, dying that way.
So to sum up: roach corpses in the home often have had all night to dry out and are on a smooth surface, making it very likely they’ll topple over. And if you’ve killed the roach with a dessicating or neurotoxin insecticide, it’s all the more likely to be on its back.
Aug. 19, 1999
By John Ruch
© 1999
Q: Why do roaches always die on their backs?
—Dumb and Dumber
A: There are a lot of people with opinions on cockroach death positions, but as far as I can tell, none of them have specifically studied the matter.
So be warned that the following answer is really just an educated guess that will hopefully one day be tested by some grad student, perhaps in his or her undoubtedly cockroach-ridden campus apartment.
The most important observation, from entomologists and pet store owners, is that cockroaches do not always die on their backs. Sometimes they die very much upright.
So I think our question actually is: why are roaches usually found dead on their backs? It’s a subtle but important difference.
Many insects tend to topple onto their backs when incapacitated, especially those with a flat back and legs positioned directly under the body. Flies are the classic example.
Roaches have a similar design, but a lower center of gravity. They probably need a stronger force than gravity to topple them over. Dehydration may be the destabilizing factor.
Insects are extremely susceptible to dehydration. Shortly after death, their legs dry and curl up. This makes toppling over almost inevitable. Ohio State University entomology associate Kyle Jordan said this is a common problem when mounting insects for display: “They’re very difficult to get to stand up. They’re unstable.”
Roaches in the home are usually found on smooth surfaces in the bathroom or kitchen. While a healthy roach is pretty good at righting itself, the smooth surfaces no doubt aid a sick or dead roach in toppling over.
If you know roaches are in your home, you’re probably also trying to poison them. Many off-the-shelf insecticides are neurotoxins that cause spasms and uncoordination. Between those two symptoms, roaches commonly fall onto their backs and are unable to right themselves, dying that way.
So to sum up: roach corpses in the home often have had all night to dry out and are on a smooth surface, making it very likely they’ll topple over. And if you’ve killed the roach with a dessicating or neurotoxin insecticide, it’s all the more likely to be on its back.