Question: Why do caterpillars turn into butterflies?
Answer: It's so ostentatious. A caterpillar is a fine little creature all by itself. Why metamorphose? There seems to be no obvious reason why it shouldn't continue to be a caterpillar, find a caterpillar mate, and have lots of baby caterpillars.Instead it goes through this wild, garish, hysterical transformation into a winged insect.
The reason: It allows the creature to exist in two different habitats. (You may now smack your forehead in the international gesture of I-knew-that.)
Caterpillars eat leaves. Butterflies drink flower nectar. One generation doesn't compete against its offspring for the same supply of food. The young and old remain independent. (The Social Security system is based on a similar concept.)
"It allows the insect to exploit completely different resources as an adult versus a caterpillar," says Don Harvey, a zoologist at the Smithsonian Institution.
We asked him what the creature is officially called. Is it a caterpillar that becomes a butterfly or is it a butterfly that dithers around for a while as a caterpillar?
He said it's a butterfly. Always. First it's a "butterfly egg." Then a tiny little butterfly larva hatches - that's the caterpillar. It gnaws on stuff and gets bigger, doing a lot of nutritional "leg work" dare we say. Eventually the caterpillar attaches itself to something, spins a cocoon of silk around itself, gets very still and undergoes the transformation into a pupa.
The pupa essentially forms inside the larva. The skin of the caterpillar splits, and the squishy pupa inside hardens with exposure to air.
Now you have a creature that can't move and has no mouth parts, no legs, just a protective shell - it's how the presidency would be if designed by the Secret Service. Inside this thing, the adult forms. What had been the caterpillar's eyes are reabsorbed. So too are the internal organs recycled. There is a complete metamorphosis. The adult emerges and gradually spreads its wings.
"It's really quite a miraculous process, because what happens is basically there's a complete breakdown and rebuilding up of the structures, the internal structures, and also the external structures, during the pupa stage," says Harvey.
Other creatures do the same thing. Moths, flies, bees, wasps. But the thing about caterpillars is that they are more impressive than the larvae of most other metamorphosing creatures. For example, a fly larva is a maggot. We are not so impressed by the desire of a maggot to transform itself into something better.
Question: Why does an eye chart always have an E at the top?
Answer: As everybody knows, such charts were invented by Herman Snellen (1831-1908), of the University of Utrecht.
Snellen chose the E because it is a hard letter, particularly the way it is printed, all bunched up, almost a solid block of type. Something like an A or an L is just too easy.
Below the E on the original Snellen chart is an F and a P. Below that, a T and an O and a Z. There have been variations on the chart over the years, but that's still the standard model.
The problem is, it's an inexact way to measure vision. Your vision is judged according to how many letters you can see on a given line. But there's a fudge factor. You don't need to get every letter right. You can miss one. Maybe the doctor will decide that you can miss two. It's kind of vague.
Also, there are more letters on the lower lines than on the higher lines. That doesn't really make sense. For example, to have 20/40 vision you need to identify at least four out of five letters on the fifth line down, but to have 20/20 vision you have to correctly identify at least 7 out of 8 letters on the seventh line. A better chart would have the same number of letters on every line.
Another problem is, people can cheat.
"In reality, that's a very poor way of testing. First of all, because it's always sitting out for the patient to see," says Edward "Ted" Murphy, director of the General Eye Service at Massachusetts Eye and Ear Infirmary. He remembers that one year, the players for the Boston Celtics visited him to have their eyes checked.
"They stood around and memorized the chart. Because they're so competitive. They were working at it as though it were a drill."
The Mailbag: Swanson S., of Clare, Mich., wants to know how credit cards are validated by store clerks. "Where is this electronic wizardry accomplished? Is there a central clearinghouse?"
Dear Swanson: Glad you asked. The Why staff always worries about centralization of power. If there was one clearinghouse for all credit card purchases, it would be too easy for a madman to take it over. He could threaten to cancel every card in America. We would have no choice but to agree to let him be the official Ruler Of The Planet.
But fortunately there's no central clearinghouse. We can tell you what happens with a Visa card because they sent us a diagram. The merchant swipes your card through a gadget. Your number goes to a Visa switchboard of sorts ("Visanet"). The information is directed to the bank that issued you the card in the first place. The bank's computer then sends the approval or rejection back through the switchboard to the merchant.
The point is, it's a decentralized process. Lots of banks are checking up on people at any given moment. Bad news for world-domination-craving madmen.