Wikipedia:Reference desk/Archives/Science/2013 July 14

= July 14 =

Need help identifying a catapillar
Spotted this little guy as I was working in my garden in Southern Norway, and am at a complete loss for what he is. He was munching away on a young aspen, and is roughly 4-5 cm long. Does anyone know what species he belongs to? WegianWarrior (talk) 13:58, 14 July 2013 (UTC)
 * Looks a lot like this one, which I found by googling [yellow caterpillar], and which is called a Canadian Yellow Caterpillar. ←Baseball Bugs What's up, Doc? carrots→ 14:08, 14 July 2013 (UTC)


 * It's had a long swim from Canada to Norway! Agree it looks the same, but caterpillars are generally known by the name of the butterfly or moth that they pupate into. Alansplodge (talk) 14:38, 14 July 2013 (UTC)
 * Gotcha! It's an Elm sawfly, Cimbex americana. I found it through this forum which reports sightings in southern England, despite it being a native of North America (apologies to Bugs). It is "also know to feed on willow and some other plants" aspen being a member of related to the Willow family. Alansplodge (talk) 15:09, 14 July 2013 (UTC)
 * Here's a picture of an adult elm sawfly. Alansplodge (talk) 15:19, 14 July 2013 (UTC)
 * Any idea what the adult stage of the Canadian yellow is? ←Baseball Bugs What's up, Doc? carrots→ 17:17, 14 July 2013 (UTC)
 * Bugs, please follow my link to the topix.com forum in my post above and read the thread - this is also the source of your photo. Alansplodge (talk) 19:25, 14 July 2013 (UTC)
 * If I'm reading that correctly, it's not a "Canadian yellow caterpillar", but actually just another photo of the larva of an elm sawfly. ←Baseball Bugs What's up, Doc? carrots→ 21:15, 14 July 2013 (UTC)
 * Correct. Alansplodge (talk) 07:27, 15 July 2013 (UTC)
 * Thank you all for helping out - and it certainly explains why I found no references in my Norwegian bug-books. WegianWarrior (talk) 17:31, 14 July 2013 (UTC)
 * Note that this is not a caterpillar - just looks like one. It's a member of the order Hymenoptera, and as the pictures linked above show, the adult is more like a wasp than a moth. -- Scray (talk) 17:51, 14 July 2013 (UTC)
 * Right, technically caterpillar is restricted to the lepidoptera, though informally, caterpillar sometimes means "crawly guy with legs" It is definitely a larva, but most people wouldn't call this sawfly larva a grub... so probably just larva is the best term. SemanticMantis (talk) 19:16, 14 July 2013 (UTC)
 * (Edit conflict) Yes, this blog says "True caterpillars have no more than five (5) pairs of prolegs, the “false legs” along the length of the abdomen that look like suction cups. Sawfly larvae have seven (7) pairs of prolegs." Alansplodge (talk) 19:20, 14 July 2013 (UTC)
 * As a side point of interest, sawfly larvae are often studied as a way of seeing into Evolution_of_eusociality, because the larvae exhibit some presocial behavior, while the adults are solitary. SemanticMantis (talk) 19:21, 14 July 2013 (UTC)


 * WegianWarrior, if you could update the details on your image, I can add it to our Sawfly article (there's a space waiting to be filled and it's a great photo). Alansplodge (talk) 09:10, 15 July 2013 (UTC)


 * Thank you - I just updated the description and requested a rename to a more suitable filename (ie "File:Elm sawfly larva (Cimbex americana).jpg"). WegianWarrior (talk) 11:22, 15 July 2013 (UTC)
 * It now adorns our article. Alansplodge (talk) 17:09, 15 July 2013 (UTC)


 * It looks so much like a new variation of Peep, I want to nibble on it. :-) StuRat (talk) 18:40, 15 July 2013 (UTC)
 * I do hope you are in the habit of frying your peeps first, then. μηδείς (talk) 02:23, 17 July 2013 (UTC)

Heavy legs
A friend said her legs felt heavy, so I was wondering how to measure their mass. I was modelling a leg as a rod with a variable mass distribution joined by a hinge to another rod representing the body also with an unknown mass distribution along it. Assume the axle between has zero mass,, you can have a second equal leg but it doesn't make any difference that I can see. It certainly can't be done by just measuring where the centre of gravity is with the leg in various positions and I don't see that measuring the moment of inertia is any help either.

Anyone like to suggest a way I could measure the mass of a leg in situ or do I have to tell her that unfortunately I really will need to cut off her leg to measure it? ;-) 21:08, 14 July 2013 (UTC)


 * A simple and approximate way would be to sit relaxed in a chair or lying down with the leg horizontal and rest the heel or calf on a bathroom scale. By relaxing, the leg muscles should neither push down on or lift the leg, and the hip joint should act as a simple hinge. An inaccuracy is that part of the weight is supported at the hip.and the hip and the scale would provide equal support only if the leg were of constant unit mass per unit length, which is not the case. .Edison (talk) 21:37, 14 July 2013 (UTC)


 * Unfortunately even if all the mass in each rod is concentrated at one point that doesn't work. If one keeps mr constant for each rod where r is the distance from the pivot and keeps the sum of the two weights constant one can vary the masses and not distinguish by those type measurements. One can move a mass over from one rod to the other without making any difference, for example split one in two and move half twice as far away and the other to the pivot. Then amalgamate that mass at the pivot into the massa in the other rod moving both to their common centre of gravity. There's no way to distinguish these two cases by these type measurements. Dmcq (talk) 23:11, 14 July 2013 (UTC)


 * Alternatively, you could measure the volume of the leg using a bath, and find the density using a CAT scanner, and multiply the two values.-- Gilderien Chat&#124;List of good deeds 21:51, 14 July 2013 (UTC)
 * That does sound like a possibility, not exactly a pure science method but probably very effective. I had a look at body fat percentage and I remember reading a while back about how they measured the volume of the lungs by the percentage of gas in exhaled air but I can't find there, anyway they seemed to do quite complicated things just to do that. I wonder if anyone just uses a scanner for that sort of thing nowadays. Dmcq (talk) 23:30, 14 July 2013 (UTC)
 * We have an article on Heavy legs, incidentally. Tevildo (talk) 23:01, 14 July 2013 (UTC)
 * Gosh Wikipedia does have an article on everything. Thanks very much. I'll tell her she's suffering from hypercondria ;-) 23:16, 14 July 2013 (UTC)


 * No, don't do that. It will serve no purpose and will be seen as a negative comment. Guide her towards the article and let her draw her own conclusion. and its hypochondria. Richard Avery (talk) 06:50, 15 July 2013 (UTC)

Place a large garbage can in a broader, shallower pan that will hold the overflow. Have her slowly get in the garbage can without sloshing. Measure the overflow, and assume she weighs the same as the displaced water. Also, a feeling of heaviness in the legs can be the sign of a severe medical condition. Have her call her doctor. μηδείς (talk) 00:40, 15 July 2013 (UTC)
 * Here's a reference> An article in a journal which discusses "heavy legs." Edison (talk) 01:49, 15 July 2013 (UTC)
 * There are even worse medical reasons than edema that can cause such symptoms, so, again, if it is a symptom and not just "do these pants make me look fat" she should contact a doctor immediately. μηδείς (talk) 03:25, 15 July 2013 (UTC)
 * She's quite healthy no worries - she was dancing and it had been a hot day. It's just me taking what's said literally and wondering about it. Anyway I rather like the one about the large garbage can, I think I'll suggest that one thanks ;-) Dmcq (talk) 07:20, 15 July 2013 (UTC)
 * A leg could be "heavier" because the volume was constant and the density increased, or because the volume increased at constant density, or some combination. One measurement would be to measure the circumference of ankle and calf when the legs are "heavy" and when they are not, to see if the volume varies. Edison (talk) 18:30, 15 July 2013 (UTC)
 * Severed legs aren't that hard to come by, either. Accidents, aggravated assault, etc. Those who sever serve in the military run a nonnegligible risk of losing a leg in a war, etc.
 * Maybe not exactly "not hard" but not extremely rare either. There should be some data on severed legs and their weight. Not sure how "available", but anonymized data should exist quite abundantly. - ¡Ouch! (hurt me / more pain) 13:21, 16 July 2013 (UTC)
 * Quite hard to search for. I searched for "severed leg" + weigh, and excepting the three words "RuneScape" (which was the first return), "washed", and "ashore" (we need fresh legs). Still, the returns are usually about the victim's weight, or about items on sale (practical jokes (I hope, had to kill SafeSearch!)) - ¡Ouch! (hurt me / more pain) —Preceding undated comment added 13:30, 16 July 2013 (UTC)