Science

With some exceptions, spiders in temperate regions have one-year life spans, with the females outliving the males by weeks or months. Perhaps the most interesting exceptions belong to the family Lycosidae, or wolf spiders. Some members of this family live in elaborate silk-lined underground burrows. The females protect their eggs in sacs that they carry … Read more

Unfortunately, no. There are many species of mosquitoes, perhaps 3,000 worldwide and 150 in the United States. The females, which seek a blood meal to produce eggs, have many different kinds of feeding habits. While many of the mosquitoes that carry disease are most active at dawn and dusk, even they may be roused to … Read more

Scorpion experts have found that scorpion species with smaller and more slender claws typically have more toxic venom. But just as with bee stings, any scorpion’s sting can be fatal to a person who is severely allergic to it. Toxicity of the venom also varies by species and prey. A species’ particular cocktail may contain … Read more

How high an insect can fly depends on air temperature. Generally speaking, most insects can fly as long as they stay in air above 50 degrees Fahrenheit. If the air temperature at ground level is 90 degrees, the 50-degree border is around 6,000 feet; if ground temperatures are in the 70s, the ceiling is around … Read more

You may have observed female dragonflies depositing their fertilized eggs into the water, where they will hatch into larvae. The eggs are sometimes inserted into underwater plant stems and sometimes smeared onto the surface of the water. More than three hundred eggs may be laid at one time. Sometimes several hundred females lay their eggs … Read more

That is the right time of year for the eastern monarchs’ migration, and they do congregate in Cape May, New Jersey, by the thousands. The monarchs seen in and around New York City are flying through on the way to their wintering sites in the mountains of central Mexico. The butterflies seek out microclimates congenial … Read more

The energy is gathered from nectar, and the butterflies that make the trip, those born in the early fall, are able to convert nectar into fat. Those born in September know to fill up on nectar. Their abdomens get really large. Unlike the other generations, these monarchs have a little area of fatty tissue where … Read more

While they do not exactly scream, some caterpillars have noise-making organs, and the sound they produce is used to call in troops of ants to protect them from predatory wasps. The noise has an average frequency of 1,877 hertz, which would be audible to human ears if it were not so very faint. Some noisy … Read more

If there was any foreleg contact or waving about of antennae by the ants, some communication may have been involved. But the wide range of communication methods among ants is weighted heavily toward chemical signals, and visual signals have not been solidly documented. Ant communication, which has been extensively but not exhaustively studied, includes tappings, … Read more

Several ant species “herd” the small pear-shaped insects called aphids and “milk” them for a sweet fluid that they excrete after feeding on sap from roots or leaves. They are sometimes called dairying ants. Ants that “milk” root-eating aphids often dig them chambers to serve as “barns.” The ants protect their aphids, carry them from … Read more

Brain wrinkles seem to have more to do with what makes humans smarter than lower animals than with what might have made Einstein smarter than you. In normal human brains, large grooves called fissures, small ones called sulci, and outward folds called gyri follow a standard plan from person to person. Lower animals have smoother … Read more

The stomach is not essential for human survival. Many people have survived and adjusted to total or partial surgical removal of the stomach because of diseases like stomach cancer. The stomach is essentially a reservoir that allows people to eat the quantity of food they want, emulsify it, and pass it gradually into the small … Read more

Like other important organs, teeth have nerves for sensation and protection. The diseased “nerve” removed in a root canal procedure is the common term for the combination of nerves and blood vessels that form pulp, the soft interior of the tooth. There is also a bundle of nerve fibers in the ligament that attaches the … Read more

If the lump is stress related and does not involve serious difficulty in swallowing, it is probably just an exaggerated awareness of the epiglottis or spasms of muscles surrounding the throat. After ruling out physical ailments that can cause the feeling of a lump in the throat, like throat cancer or esophageal reflux, in which … Read more

Yes, eventually, but it is not a simple matter of sleeping longer on a weekend after being denied adequate sleep for some days. In extreme cases, experts say, you may need six weeks of adequate sleep to repay a long term sleep deficit. Several studies have found that the amount of recovery sleep required to … Read more

The small piece of soft tissue dangling over the tongue is the uvula. It is variously described as U-shaped or tear-shaped, or classically speaking, grape-shaped; its name comes from the Latin word for grape. While some anatomy experts think it is only a vestigial organ, not all would agree with your teacher that it has … Read more

Many of the explanations offered for the sharp pain runners feel during hard breathing, usually on the right side, involve muscle stress or spasms in or near the diaphragm. Because the muscle stress is probably caused by a rhythmic, repetitive activity, the solution is to develop techniques to break up that stressful rhythm. Runners could … Read more

The brain can tell which tickling sensations are caused by one’s own actions and gives them low priority, so that it can be more receptive to sensations from outside sources that may be more urgent. One study suggests how brain areas may interact to do this. In the study, a magnetic resonance imaging device scanned … Read more

You are not alone, because about 30 percent of the population seems to have the same problem. The classic ice cream headache is a stabbing pain that usually peaks after thirty to sixty seconds, though it can last up to five minutes. A doctor who gets such headaches, Dr. Robert Smith, founder of the Cincinnati … Read more

Not according to experts. In fact, children can focus up close without eyestrain better than adults. That is because the lens, which changes its focus for nearby and faraway viewing, tends to lose some of its flexibility as people grow older. Usually, sitting very close to the television set is a habit that children grow … Read more

Ordinary hiccups, resulting from things like overeating and stress, are usually benign. But hiccups can indicate a serious problem, and a prolonged, uncontrollable bout may lead to debilitating consequences like fatigue, weight loss, depression, problems with heart rhythm, esophageal reflux, and possibly exhaustion and death in a weakened patient. In a famous case, Pope Pius … Read more

Nobody has specifically studied this aspect of sneezing, but there are logical reasons that would explain why people do not sneeze overnight. The reason people sneeze is that the inside of the nose swells up, much like blowing up a balloon. When a windblown particle of anything, an allergen or a particle of dust, hits … Read more

Rigor mortis is gradual, usually noticeable about three to four hours after death, and the timing varies with several factors, including the person’s activity just before death and the temperature of the body’s surroundings. How long it takes the muscle stiffness to subside also varies, with rigidity usually reaching a peak after twelve hours and … Read more

The eyes have a very efficient radiator as well as a surface deicing system, at least in theory. The eye has a system of blood vessels that provides a constant irrigation of warm blood through and around the eyeball to keep it warm. This makes freezing very unlikely. As for the surface of the eye, … Read more

Crime novels to the contrary, it is hard to dispatch someone with a needle unless you are expertly trying. It is standard practice to make sure air is cleared from a syringe before pushing the plunger, but the chances of death occurring because of the air a fine needle might carry in a normal injection … Read more

Organs may come from newborns on up, with no specific age limit. There was more of an age limit in the past, but now it is decided on a case-by-case basis. The oldest known donor of a liver was 92, in Canada, and there was one who was at least 85 in the United States. … Read more

A keloid is a scar that does not know when to stop forming, becoming large, shiny, smooth, and often pink and dome-shaped. It is not known why some people get overgrown scars after injuries, surgery, or acne, but keloids are more common among people of black and Asian descent, so a genetic factor is suspected. … Read more

Yes, but it is not a good idea except under very special circumstances, because too high a concentration of oxygen or oxygen at too high a pressure can be toxic. For example, when a diver gets too much oxygen at high pressure, oxygen toxicity can cause lung damage and even convulsions. However, pure oxygen in … Read more

A pinched, compressed, or entrapped nerve can be surrounded by swollen tissues or impinged upon by bony processes in many areas of the body. The cause can be injury, disease, or even pregnancy. The result is pain, numbness, tingling, and weakness in the part of the body to which the nerve normally carries impulses. One … Read more

The prevailing theory involves damage to the DNA of skin cells. It is the shorter UVB rays, which penetrate only the top layers of the skin, that are suspect, while the longer and more deeply penetrating UVA rays cause wrinkles and aging. In tissue cultures, UV damages the DNA of cells, but humans have an … Read more

There are treatments for vitiligo that are at least partly effective in many cases, but its cause is still under study. A prominent theory is that an autoimmune reaction is involved. The condition may also be associated with certain ailments, including thyroid disorders, and may flare up after injury, stress, or severe sunburn. Patches occur … Read more

Exposure to the sun’s ultraviolet radiation darkens granules of the pigment melanin in the surface layers of the skin. Part of the radiation also stimulates pigment-producing cells, called melanocytes, in deeper layers of the skin, causing a delayed-reaction tan, about three days after exposure. When the top layers of skin wear off, so does the … Read more

Skin changes that cause wrinkles do accompany aging, as the deeper layer of skin, the dermis, gets thinner. But it happens more quickly in sun-exposed areas and in people who smoke. The breakdown of two kinds of molecules, collagen and elastin, is at fault. Collagen type 1 is the molecule that makes up the bulk … Read more

The vermiform (Latin for worm-shaped) appendix, a dead-end branch of the intestines, plays at least a minimal role in the immune system and is also sometimes regarded as a potential spare part for replacing things like a diseased urinary bladder. Along with the adenoids, tonsils, and spleen, the appendix is classified as part of the … Read more

Such a condition is probably an inflammatory response to the irritation of having the eyes open and exposed to the drying air. The effect is common knowledge and a clear symptom of sleeplessness but has not been completely studied. Eye lubricants and tears dry in the air and may form scratchy particles. The skin around … Read more

Ear wax, known to scientists as cerumen (pronounced suh-ROO-mun), traps dust and dirt particles to keep them from going down the ear canal to the eardrum. Besides protecting against dirt and water and lubricating the canal, ear wax is slightly acidic, so some experts say it has mild antibacterial properties and helps fight the growth … Read more

If we leave aside the possible presence of diseases like arthritis or diabetes, several mechanical factors could make standing still more tiring than walking. First, the action of the muscles in walking keeps the circulation of both blood and lymph going, preventing the pooling of fluids in feet and ankles. For another thing, when a … Read more

Liver spots, also called age spots or lentigines, are the result of hyperpigmentation, or the buildup of excess pigment in patches of the skin. Liver spots have nothing to do with the liver and most often result from a lifetime of exposure to sunlight. Other possible causes include surgery, pregnancy, and some medications. Liver spots … Read more

Sensitivity to temperature is much more complicated than a simple gender split, physiologists say. The reaction depends on many factors, such as exercise, previous conditioning, diseases, and any other tinkering with the complex system of signals to and from the hypothalamus that sets the body’s temperature controls. Some doctors suspect psychological factors make a difference, … Read more

Medical literature contains few if any cases in which people have recovered after their inner, or core, temperatures dropped below 55 degrees Fahrenheit. Core body temperature is usually measured by elec, tronic sensors inserted into the digestive tract. It cannot be measured with an ordinary oral thermometer. Hypothermia is considered to exist whenever the core … Read more

What seems like frozen fingers is very subjective and could cover a wide range of temperatures. Having fingers that are icy cold is a real sensation and can be very distressing, but it is usually not reflective of something dangerous. What is more dangerous is where one finger is cold or has changed color, or … Read more

Artificial blood will not be available any time soon, and the need for donations will remain acute for the foreseeable future. Synthesizing blood is much more complex than synthesizing insulin. Blood includes many different kinds of cells, while insulin is a protein. There are ways to make hemoglobin, the protein in blood that carries oxygen, … Read more

The most basic classification of the hundreds of ways to type human blood, the ABO system, is important because incompatible types of blood react with each other to form sticky globs of red blood cells that can cause serious and sometimes fatal blockages. The classification was developed in 1901 by Karl Landsteiner, a Viennese-born pathologist … Read more

Idiopathic scoliosis, a sideways curve of the spine of unknown cause in adolescence, is now believed to require active treatment in only about 10 percent of cases. When treatment is called for, a cast or a device called a Milwaukee brace is widely used. At least 60 percent to perhaps 80 percent of the cases … Read more

Morning sleepiness in teenagers (or in anyone else) may have a cause as simple as lack of sleep, perhaps because of too much homework after a part-time job, followed by television. In that case the cure may be to sleep more, cut down on some sleep-robbing activities, and gradually change bedtime and waking time in … Read more

The description fits what doctors still call growing pains, or benign limb pains of childhood. The suffering is real, though the source is still not understood. Most pediatricians do not believe growing pains are actually related to the child’s growth. For one thing, the location is ill defined, not specifically at the limbs’ growth plates, … Read more

Experts suspect that the problem is not that tired parents are using strollers while shopping, but rather that they may be preventing their children from moving enough the rest of the time. Child development specialists think that freely crawling, cruising, and toddling are a normal progression in a child’s physical and cognitive development. But as … Read more

There is no definitive answer, but its structure suggests a key role in the strong grip for hanging and power grasping. The middle finger’s length is one aspect of hand evolution that people have in common with apes. For many primates, the middle finger is the functional axis of the hand and the longest finger. … Read more

Your adult height will probably be somewhere in between. Some rough estimates can be made based on the growth patterns of many children. These methods assume that there is no disease or hormonal problem to hinder your genetic potential. Because height at the age of 3 is about 60 percent of adult height for girls … Read more

Slightly more than half of all twins born are male. In conjoined or Siamese twins, the picture is complicated both by their extreme rarity and by their very low overall survival rate, which is variously given at 5 percent to 25 percent. Conjoined twins are always identical, because they always come from a single fertilized … Read more

The advantages for girls begin even before birth, and like so many other differences between the sexes may be tied to hormones. For example, significantly more male fetuses are spontaneously aborted or stillborn. The reasons need more investigation, but they seem to include sex differences in chromosomal structures and possibly a slower maturing of boys’ … Read more

Many studies have found a relationship between birth order and birth weight, with the later-born children in a family tending to be larger, and birth weight has some correlation with eventual height. For example, a 1988 study at the Children’s Hospital of the University of Kiel, Germany, investigated adult height in families with three or … Read more

In fact, each year more males are born than females. The normal slight excess of male births is usually attributed to the slightly greater motility of sperm carrying the male, or Y, chromosome. It was recently discovered that in the average ejaculation, there are slightly more sperm carrying the X chromosome, necessary for conception of … Read more

Fetal urine is the main component of the amniotic fluid that bathes the developing fetus. It is excreted into the fetal sac inside the womb as the fetus develops. Normally, the fetus “breathes” this fluid into its lungs, and it is essential for the normal development of the lungs. The fluid contains some fetal cells, … Read more

Most gulls do not have feet that are adapted to perching in trees and clinging to tree branches. Most have slightly webbed feet that help them move about in the water, so when they are on land, they do better walking on rocks or soft surfaces like sand. Pure probability also puts gulls on the … Read more

Evolutionary biologists have suggested that morning sickness is a mechanism to help women avoid noxious substances that might harm the fetus at an early stage of development. Formerly, scientists had assumed that the sickness early in pregnancy was related to a sharp rise in the hormone estrogen. But as some scientists point out, the sickness … Read more

Woodpeckers like the acorn woodpecker of California, which hits the wood with its bill at speeds of 12 to 15 miles an hour, manage to keep their wits because their brains are held firmly in a case, which acts as a shock absorber. The bird’s body also moves in a single plane like a metronome, … Read more

Bird droppings combine the whitish waste products processed by the liver and kidneys with the darker wastes that come from the digestive tract. In birds, the nitrogen-rich wastes are turned into a white-colored paste that is composed mostly of urates. The urates often form a separate white blob, as anyone who has worn a new … Read more

There are three kinds of evidence. First, there is epidemiological data from studies of AIDS outbreaks. For example, in sub-Saharan Africa, where mosquitoes are extremely plentiful, the very people who would get bitten most, young children who are outside playing, comprise the one group that is not HIV-infected. The AIDS epidemic is among the sexually … Read more

ARDS, which stands for acute respiratory distress syndrome, or sometimes adult respiratory distress syndrome (to distinguish it from a lung problem in newborns), is not a disease itself, but a type of severe acute lung dysfunction that can result from disease or injury, according to the ARDS Support Center, a clearinghouse for information. The condition … Read more

Foot-and-mouth disease is a danger only to animals, not to humans, and the chance of getting mad cow disease from dairy products is zero to almost zero. The risk is so slight that there is an exemption allowing the importation of milk from countries where mad cow disease has been found. Transmissible spongiform encephalopathy, or … Read more

Cat scratch fever or cat scratch disease is a mild flu-like infection, usually causing swollen lymph nodes and a low-grade fever, that was first described in the 1950s as being associated with cat scratches, especially from kittens. The infection usually goes away by itself in a few weeks and can be treated with antibiotics, but … Read more

Try a longer vacation. Altitude sickness is not linked to a person’s general condition but to specific adaptations to high altitudes; even puny permanent residents are usually immune. Medical experts say the body usually adjusts within a few days to the complex changes in blood chemistry that come about because of the relative shortage of … Read more

From the human point of view, some viruses can be useful, potentially useful, or at least interesting. Under the “interesting” heading would fall the mosaic virus, which produced the fantastically variegated tulips of the tulipomania investing craze in seventeenth-century Holland. The rare infected bulbs were treated almost like a currency with a constantly multiplying value … Read more

It is not cold feet and wet heads that are the problem, infectious disease experts say, but the fact that human beings are warmth-loving social animals. At least in cold climates, widespread outbreaks of diseases like colds and influenza tend to start in winter months, when people spend more time together indoors in close quarters … Read more

Immunity is long-lasting because some of the many kinds of cells that make up the normal human immune system are naturally able to retain a “memory” of the defense efforts aroused by certain infections or vaccines. There are many kinds of immune cells, including T cells and different types of white cells. Their interaction with … Read more

There is no simple answer, but in general, this is very unlikely. In theory such reinfection is conceivable, but there are no documented cases of it. The possibility would depend on the organism and how the person’s immune system responded to it. If a pathogen is on the skin a long time, the person has … Read more

Polite East Asian people with a cold may wear a mask with the aim of preventing its spread; this is especially common in Japan. In China, the idea may be to cut down infection or it may be a reaction to high levels of visible pollution; in some of China’s industrial areas, masks are worn … Read more

There are no guarantees, but there are some ways to cut your risks. The most important are avoiding crowds, especially during the peak cold seasons of September, late January, and April; avoiding people who obviously have colds; avoiding shaking hands with people who might have them; avoiding rubbing the nose and eyes; and washing your … Read more

They are referring to how the germs react to one of the basic tests in bacteriology, the Gram stain or Gram’s stain, which distinguishes between two major classes of bacteria by how they take up certain dyes. On a microscope slide, heat-treated gram-positive bacteria take up a purple dye (originally gentian violet), which is then … Read more

There are viruses that infect disease-causing bacteria, as well as many other bacteria. Called bacteriophages, meaning bacteria eaters, they were discovered during World War I and named in 1917. Much smaller than the bacteria they attack, bacteriophages cannot grow and multiply on their own. Instead, like other viruses, they attach themselves to the surface of … Read more

There are three likely explanations, based on recent research. First, what do you eat and drink? A lunch high in carbohydrates, especially if no protein is eaten along with bread and milk, is likely to produce calm to the point of sleepiness, because of the complex role of carbohydrates in shifting the balance of neurotransmitters … Read more

Some disease-causing organisms, or pathogens, can thrive and multiply for some time on an object like a phone receiver spattered by the saliva of an infected person. But most bacteria and viruses quickly die when moisture disappears, usually after one or two hours for the saliva spray. Different pathogens have different survival times, ranging from … Read more

There is both concern and controversy over mercury in fish, but an occasional tuna fish sandwich for an adult who is not going to become pregnant is not the main worry. The biggest concern is the risk to a fetus. Mercury builds up in muscle cells of fish and in those who ingest it, and … Read more

Kaolin, also called China clay, is a chalky rock composed chiefly of kaolinite, together with quartz and mica. It is formed by the weathering of aluminum-rich silicate rocks, especially feldspar. Over the ages, the crystals wash into large sedimentary deposits. Purified kaolin in a suspension with pectin from apples has long been used to fight … Read more

Milk thistle does contain chemicals called flavones that appear to benefit the liver, but these compounds are not very soluble in water, and the tea has only about one-tenth the strength of the original plant material. In fact, the chemicals are poorly absorbed through the gastrointestinal tract and would probably be medically effective only if … Read more

Calcium citrate, the type found in calcium-enriched orange juice, is less likely to cause stomach upset than other forms. Calcium carbonate and calcium gluconate are the two forms that are most common in supplements; they both tend to be adequately absorbed. Calcium citrate is a good alternative, because it is very well absorbed and also … Read more

The assumptions of the question are not totally true. It’s not just drinking, but where you drink and what kind of clothes you have on that determine whether the body ends up warmer or colder. What happens is that alcohol causes the blood vessels in the skin to dilate, so that more blood passes through, … Read more

The Physicians’ Desk Reference for Nonprescription Drugs (PDR) does not advise against taking normal doses of aspirin in addition to acidic foods or alcohol, itself a powerful drug, but there may be deleterious interactions for some people. That is because aspirin is an acid, acetylsalicylic acid, and when aspirin is taken with acidic foods and … Read more

Caffeine is not a direct stimulant; instead, it blocks the action of another chemical, naturally present in the human body, that has a calming effect on the activity of cells, especially those in the brain and spinal cord. Caffeine, found in tea, coffee, and cocoa, is one of a class of chemicals called methybcanthines that … Read more

Quinoa is a significant source of calcium, but you would have to eat a large amount of it to get a full daily supply. The National Academy of Sciences recommends 1,000 milligrams of calcium a day for most people, more for those over 50, and according to the United States Department of Agriculture, a cup … Read more

They are usually talking about six to eight glasses of 8 ounces each, for a total of 64 ounces a day. It does not hurt to drink more, especially if you are exerting yourself. You might weigh yourself before and after a workout and drink 16 ounces of water for every pound you lose. With … Read more

Not any more than eating enough of any other protein. If someone is severely protein deficient, high quality protein like that in gelatin might make a difference, but the average person gets plenty of protein. It’s the same with calcium. It would help your nails if you were totally deficient, but if your bones are … Read more

Repeated studies have failed to find any link between eating chocolate (or anything else) and teenage breakouts. As long ago as 1950, a study by a dermatologist compared the results of giving teenagers with acne candy bars that just tasted like chocolate and those made with real chocolate. Photographs showed no difference in new breakouts. … Read more

The short answer is that aflatoxin is of very little concern. Aflatoxin is produced by the fungus Aspergillus flavus, and most people don’t eat moldy food, because it tastes bad. Documented human aflatoxin problems usually occur in tropical countries, where the wet climate is conducive to mold growth, or in extremely poor ones, where people … Read more

It can be either very healthful or very noxious, or both. A study by scientists at the U.S. Department of Agriculture, done with money from the Peanut Institute, suggests that peanuts may contain enough resveratrol, the compound in red wine associated with a low rate of heart disease, to be helpful to human health. The … Read more

Yes, if it is a real cheese pizza with real tomato sauce. For a complete diet, first you need to consume a sufficient quantity of food to get enough calories. Then you need a good source of protein and a supply of certain essential nutrients, like vitamins B12 and C, found only in certain kinds … Read more

The most likely culprits for yellow clothing stains are body secretions called apocrine sweat and sebum, the oily secretion of the sebaceous glands. Deodorants and antiperspirants may also play a role. The sebaceous glands are usually associated with hair follicles. Cells filled with fatty droplets die and burst, providing lubrication for the skin and hair. … Read more

Perfect pitch, which is also called absolute pitch, is the ability to name any note (such as A, B flat, C sharp) just from hearing the tone, without reference to other notes in a scale. Relative pitch, which is far more common, is the ability to tell what note is being played by judging the … Read more