Wikipedia:Reference desk/Archives/Science/2017 August 10

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 10

Rapid spiderling growth

A few weeks I noticed a female Daddy longlegs (mommy longlegs?) with an egg sack in the corner of my bathroom. Now, normally any spider is gross enough to get an eviction, promise of yet more spiders most assuredly included. But this particular spider had only five legs and I figured she'd earned a rest, so I left her alone. About a week ago, the eggs hatched. At first they were so small it was difficult to make out their indivual legs with the naked eye, but just one week later, they have almost tripled in size. And yet, no immediately obvious prey or other source of nourishment. So my question is this: where is all of this mass coming from? Are the babies born with metabolic reserves in a more compact form, which energy they can tap to quickly develope? Or does the mother provide some kind of nourishment? Spider says mothers in some species will regurgitate food for young, but it is unclear if they only do this with recently caught prey; there has been no immediately obvious prey of any size in or below the web, but I can't rule out a quick snack has been missed. Thoughts? 2001:4B98:DC0:47:216:3EFF:FE3D:888C (talk) 12:03, 10 August 2017 (UTC)

Only 2 cents thoughts. The most simple is usually the better: they eat prey according to their size, that you cannot see (including their own bro, maybe), but you probably thought it yourself already. Also, spiders may eat silk, and things (living or not) that got stuck to it, that may be significant food for a small enough spiderling. And, obviously, most new mass will come from water, considering the water proportion in living being. I hope someone will bring some better answer. Gem fr (talk) 12:33, 10 August 2017 (UTC)

Prey as small as that are unlikely to be caught in most Pholcidae webs as they do not have strong adhesive quality; their webs are arranged by filaments suspended at every convenient angle, so as to entangle prey, but prey so small as to be tiny compared to even the young spiders described by the OP are unlikely to be caught by such webs. Some spiders do consume their webs, but rarely do they have much nutritional value; more often they do it in order to adjust their nests. I think the OP's original guess is most likely to be right; these spiderlings are probably just developing from their original high-energy reserves. Consider that they do, afterall, develop from embryo to post-embryo (hatchling) without consumption. Also, often the legs of spiders will develop fastest in the first molts; this results in their appearing to grow faster than they in fact are in the aggregate, because the legs, while not a huge additional amount of mass, lead to a significantly larger leg-span and thus perceived diameter.

All of that said, the OP should be on the look out for these spiders to disperse soon. Spiders are highly famine resistant creatures (they are capable of entering into period of highly prolonged and substantial stillness, thus modulating their metabolic rate), but the one exception is early life, for exactly the reasons the OP is noticing here: A) they are developing and burning through their reserve energies and B) they are relatively helpless to collect prey. They make up for this in part by having large numbers of offspring, some of which will be more fortunate than others in securing those early meals, possibly using their mothers nest (though, to my knowledge, Pholcidae do not share captured prey with anyone, not even family), but more likely after securing their own. Cannibalism is also quite common among the young of many species. The Pholcidae family is also known for their willingness to tresspass into the webs of other spiders to steal their food or even kill the inhabitants and/or eat their eggs, so there's that too. Here's some useful additional reading: [1], [2], [3] Snow ^{let's rap} 13:39, 10 August 2017 (UTC)

Shivering

At what temperature does shivering start at? Assuming wearing light clothes. — Preceding unsigned comment added by 5.200.42.234 (talk) 14:20, 10 August 2017 (UTC)

It is not a set temperature. Some people lose the shiver response due to age or injury and never shiver. Some people shiver when hot (fever chills). Normal shivers are triggered by core body temperature vs skin/spinal temperatures and vary from person to person. 209.149.113.5 (talk) 15:37, 10 August 2017 (UTC)

An HVAC book may have that study where they kept people at various temperatures for hours/temperature and I think the average was around 55°F. Sagittarian Milky Way (talk) 16:05, 10 August 2017 (UTC)

You can train yourself to not shiver and tolerate extreme cold much better, see here, and here, and here. Deep and fast breathing exercises are important if you want to tolerate extreme cold for a long period. In the beginning you'll hyperventilate when doing that, but you then train the body to burn the oxygen and produce more CO2 whenever you start breathing like that, thereby increasing the metabolic rate significantly. This allows you to sit naked in ice cold conditions without shivering, you're breathing faster and burning not the usual 100 Watts but 300 Watts or even more. Count Iblis (talk) 19:47, 10 August 2017 (UTC)

• Shivering can be a response to illness, or to perceived heat-loss through the skin, not just a low core temperature. I have reported before, my father recounts working on a windy day in West Texas in the 1960's. The temperature was 70, and him being 6'2" and weighing 250 lbs, that would have been a comfortable day in the Philadelphia shipyards where he apprenticed. But the humidity was 02% and he started shivering as soon as he got out of the car at the worksite, and had to get a winter coat (to a Philadelphian) to work outdoors. μηδείς (talk) 01:59, 12 August 2017 (UTC)

Is there a phobia of being in a building much narrower than it's tall?

Sagittarian Milky Way (talk) 15:34, 10 August 2017 (UTC)

Nearly every named "phobia" you've ever heard of is a product of folk psychology and is not a recognized mental disorder, as defined by actual psychologists, such as the DSM-5. The only types of phobias widely recognized are social phobia, specific phobia, and agorophobia. There are hundreds of dubious sources that will claim to give faux-Greek names to phobias (like "coulrophobia", fear of clowns) but these are NOT recognized by medical professionals as distinct disorders, instead they are all classified under one of the other phobias. A fear as specific as you name is known as a type of specific phobia. --Jayron32 16:04, 10 August 2017 (UTC)

One of Steven Wright's early jokes was, "I was out walking my dog today... on the ledge. Some people are afraid heights. I'm afraid of widths." ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:37, 10 August 2017 (UTC)

Mother of all arachnophobia

Recently I was reading a funny story about arachnophobia - a woman on a field expedition was climbing a steep hillside and abruptly backpedalled, frantic, finally yelling a distressed cry of "Sp-i-i-i-der!" And yet --- it turned out her fear was entirely justified, because the story occurred in Australia. Unlike in the U.S., where arachnophobia is a joke, almost seen as a psychiatric ailment, everything in Australia is apparently out to kill a person with poison. Which got me to thinking...

I have read that other primates have specific distress calls for poisonous spiders. Obviously any spiders of relevance would have had to be encountered by human ancestors in Africa. So ... is it possible to identify the one and only specific kind of spider, against which all human arachnophobia is directed? Is this thing perhaps more inherently terrifying than any other kind of spider, things that merely resemble it?

Starting with such ahem reliable sources as [4], I am directed in the direction of button spiders. There are images like at the top of this article which suggest that oh my, that is one scary looking spider. But can someone here do better, provide some compelling context that makes it out as the definite culprit, or proposes alternative suspects? Wnt (talk) 20:31, 10 August 2017 (UTC)

Deaths or serious injuries from spider bites are very rare even for mentioned black widow spiders. So, this can not explain arachnophobia. Ruslik_Zero 20:57, 10 August 2017 (UTC)

It still probably hurts like hell right? The level of medical technology for most of this subspecies' existence was something like drill a hole in the skull or add leeches. Spider deaths must've been more common then. Sagittarian Milky Way (talk) 22:41, 10 August 2017 (UTC)

I'm assuming that the evolution (or retention) of such an instinct would occur over millions of years. Homo habilis and Australopithecus spp. were generally shorter than modern humans from Homo ergaster on, less than 4 feet I think. I don't know if overall smaller brains would make them more susceptible to a neurotoxin than other humans with the same body mass but larger brains. I should admit that I am susceptible to a crank variant of the old (discredited) aquatic ape hypothesis, in that I am suspicious that human ancestors developed elongated feet and bipedality and fire use in West Africa, in the Okavango delta or nearby (formerly wet) terrain with regular flooding and wildfires; if this is true, then suggesting a black button spider (Latrodectus indistinctus) with the strongest toxin which lives north into Namibia is acceptable - but otherwise (where the known fossils are in East Africa) there could be a problem with the range. This spider (or our closely related black widow) seem like decent options for being 'instinctively' disturbing, but I'm not sure the black button spider is archetypal. Wnt (talk) 01:22, 11 August 2017 (UTC)

Not necessarily answering, but just linking to signalling theory and aposematism, which are somewhat on topic and interesting. —PaleoNeonate – 00:55, 11 August 2017 (UTC)

I just cannot believe that spiders were ever enough a threat to trigger an evolutionary adaptation, and turn arachnophobia into a competitive advantage. As opposed, for instance, to "mosquitophobia" (red link !), THIS would had been, and still be, a real competitive advantage, but doesn't seem very common (if it ever exist).

fear is known to be triggered, among other things, by startling quick movement of the thing; mice and spiders are both capable of this kind of movement: they just stand still, then they surprisingly dart or even jump (Salticidae) in any direction, including yours, and THIS is indeed threatening (even though you may laugh afterward of fearing such a small thing). On the other hand, when you learn (from experience, not from books), that Pholcidae do not move this scary way, you stop finding them scary.

Plus, spiders and their webs are also a thing that will surprise you in scary environments, such like caves, dark wood, or darkness of the night, and trigger Startle response (who here didn't startle when feeling a spiderweb on his face in a wood or a cellar?).

So, for my 2 cents, the simplest explanation of arachnophobia do not involve any genetic memory of any spider of the past, but rather natural association of spiders with fears: surprise movement, and fearful environments (darkness, enclosed space,...)

Gem fr (talk) 09:15, 11 August 2017 (UTC)

Interesting! Might this also be the cause of mottaphobia, given that butterflies also tend to make surprise movements, and some (like the Monarch) are also quite large? 2601:646:8E01:7E0B:21B1:8CA4:6F9F:6132 (talk) 08:33, 12 August 2017 (UTC)

We certainly do have "mosquitophobia", though it is more like "Islamophobia" in terms of the specific emotions involved. The whine of mosquitoes is uniquely annoying (well, maybe not uniquely given that flies have also been made annoying, but it is at least distinctively annoying), their bite distressing, the impulse to swat them universal. The number of mosquitoes is a critical factor that forces participants in survival shows to camp one place rather than another, more than access to food and water. But ... swatting spiders may not work like swatting mosquitoes, and unlike mosquitoes, spiders are readily avoided if one has the right emotions. Given that the bite of a button spider is regarded as a medical emergency according to our article (even though Lonely Planet assures folks button spiders are "harmless"...) I continue to think it is plausible they could arouse this reaction. Wnt (talk) 12:26, 11 August 2017 (UTC)

Formula for walking on gradients

If I burn, say, 100 calories by walking a certain distance on a flat road (0% gradient), is there any formula that allows me to calculate how many calories I would've burnt by walking the exact same distance but on a 5% uphill gradient? --90.69.12.160 (talk) 22:20, 10 August 2017 (UTC)

Find a formula for climbing, multiply your walking distance with 0.05 (5%) and use it as climbing distance and then just sum up both results. --Kharon (talk) 23:09, 10 August 2017 (UTC)

This paper looked at that question: http://jap.physiology.org/content/93/3/1039.full the study was conducted on treadmills. The metabolic cost of walking (Cw) in J/(Kg *m) was empirically determined to be 280.5i⁵-58.7i⁴-76.8i³+51.9i²+19.6i+2.5 where i is the incline.208.90.213.186 (talk) 23:14, 10 August 2017 (UTC)

incline in %?

practitioners of hiking in hill/mountains have a rule of thumb: 100 m up is equal to 1 km, as efforts go. Meaning a a 10% uphill gradient doubles the distance, and 5% increase it by 1.5.

note that this rule of thumb is pretty well in agreement with the study mentioned by 208.90.213.186, provided i is indeed in %

Gem fr (talk) 09:30, 11 August 2017 (UTC)

For time required to walk a certain distance factoring-in gradients and terrain, see Naismith's rule. Alansplodge (talk) 12:26, 11 August 2017 (UTC)