# Is a Lobster an insect? **URL:** \ **Category:** Factual Questions\ **Created:** [July 4, 2004, 11:33pm UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566 "2004-07-04T23:33:04Z")\ **Posts on this page:** 12\ **Page:** 3
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 6, 2004, 11:46pm UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/41 "2004-07-06T23:46:23Z")
> [@Derleth](#): > > A legal context as relates to anti-cruelty statutes, obviously. > > Was there ever any other context implied? And what, pray tell, is the legal definition of an “animal,” or an “insect?” ---
**Author:** ![Firx](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Firx](https://boards.straightdope.com/u/Firx)\ **Post date:** [July 7, 2004, 2:05am UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/42 "2004-07-07T02:05:48Z")
> [@](#): > > Originally Posted by **SoulSearching** > I know this is against the law that a nickel and a piano can be dropped from a skycrapper and the force of gravity is the same since they will both land at the same time. > [@](#): > > Originally posted by **David Simmons** > The “law” that you cite about a nickel and a piano is true in a vacuum. The ant doesn’t fall in a vacuum. > > Air resistance is roughly (very roughly) proportional to cross sectional area which varies as the square of the dimensions. Weight, the attraction of gravity, varies according to the cube of the dimensions. So as the dimensions get smaller and smaller the ratio of the force of gravity(weight) to the air resistance gets smaller and smaller. To something the size of an ant, the air is quite thick. This isn’t exactly on topic, but there are a few things here that ought to be cleared up. First, the ‘law’ being discussed here has nothing to do with the force of gravity. Rather, it has to do with the _acceleration_ of a body due to gravity. The force of gravity on a piano is quite different than that on a nickel - as evinced by the fact that you can hold a nickel but not a piano in your hand - but they both accelerate at the same rate in Earth’s gravity. Second, air resistance (aka drag force) is pretty well approximated by the following equations: F[sub]D[/sub] = k\*v; Re \< 1 and F[sub]D[/sub] = 0.5_C[sub]D[/sub]Ap_v^2; Re \>1000 where F[sub]D[/sub] is the drag force, k is a proportionality constant, C[sub]D[/sub] is the drag coefficient, A is the projected area, p is the density of the medium (in this case air), and v is the velocity. Re is the Reynolds number and is defined as, Re = L_p_v/u where L is the characteristic length, p is the density of the medium, v is the velocity, and u is the dynamic viscosity of the medium. So, we need to know when Re for the ant is greater than 1000. Taking L = .00635 m (1/4 in) as the length of a typical ant (we’re being generous), 1.23 kg/m^3 as the density of air, and 1.86\*10^-5 as the viscosity of air, we get: 1000= .00635_1.23_v/(1.86\*10^-5) =\> v = 2.38 m/s Since the ant falls from rest, and v = v[sub]i[/sub] + a\*t we know t = .2427 s. Also, since d = 0.5_a_t^2 (starting from rest) we know d = .289 m. So we can safely approximate the drag force with the second equation, since Re \> 1000 for the majority of the ant’s fall. Where does that leave us? Well, all of the above was merely to establish a model, so to speak, that is appropriate to the situation. Really, the ant doesn’t feel a constant acceleration equal to 9.81 m/s/s, because part of this is offest by drag. Here’s how it works: a[sub]net[/sub] = F[sub]net[/sub]/mass = (F[sub]g[/sub] - F[sub]D[/sub])/(p\*V) or a[sub]net[/sub] = 9.81 - 0.5_C[sub]D[/sub]_(A/V)\*v^2 where A is the projected area and V is the volume (density has cancelled). This is what **David Simmons** is referring to above. Note that since the volume increases with the cube but the area only increases with the square, as size increases the (A/V) term swiftly diminishes, causeing a greater terminal velocity (the velocity needed to have an a[sub]net[/sub] of zero), If we approximate an ant as a sphere with diameter .00635 m, we get A = 3.167_10^-5 m^2, V = 1.341_10^-7 m^3, and taking C[sub]D[/sub] = 0.47 (for a sphere), we get a[sub]net[/sub] = (9.81 - 55.512\*v^2) m/s/s and v[sub]terminal[/sub] = .420 m/s (In turn, this gives us a Re = 176.526. This doesn’t invalidate the model, but it means that we can’t really treat C[sub]D[/sub] as a constant anymore. But since we’re just estimating anyway, we’ll let it slide.) If we guess an ant’s mass at .1 gram, this terminal velocity means that the ant has to dissipate a kinetic energy of KE = 0.5_m_v^2 = 8.836\*10^-6 joules Which is ridiculously small. Thinking of it in terms of impulse and momentum, if a .1 g ant falling at .420 m/s hit the ground, and the impact took place over .1 seconds then the ant would feel a force of 4.204\*10^-4 N, or about 1/23 the weight of a paper clip. ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [July 7, 2004, 2:25am UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/43 "2004-07-07T02:25:43Z")
> [@Darwin's Finch](#): > > Are you thinking of [this fellow](http://www.whozoo.org/Anlife2001/chelsy/clh_Bathynomus.htm) (_Bathynomus giganteus_)? Please tell me those things never, **EVER** get out of their abysal dwellings. :eek: ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [July 7, 2004, 2:28am UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/44 "2004-07-07T02:28:05Z")
> [@Ale](#): > > Please tell me those things never, **EVER** get out of their abysal dwellings. :eek: “That is not dead which can eternal lie…” 😉 ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [July 7, 2004, 2:40am UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/45 "2004-07-07T02:40:29Z")
> [@Mangetout](#): > > Despite my reputation as a voracious gourmand and despite my curiosity, I have never yet eaten woodlice - if they were about the size of lobsters (like those so-called ‘living trilobites’ we had in that thread a week or so back), I’d be tempted. Sp if one managed to procure one of those deep-sea isopods and boil it, would you eat it? The website says the status is non-threatened, so it should be legal to go fish for some and cook 'em, right? (I saw the picture of the thing and immediatly though it looked like those bugs from Starship Troopers. Not the ones that the people fight, but the smaller ones they disect in high school.) (Oh, and from this thread, I also now know why Dr. Zoidberg is from Decapod 10. 😃 ) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [July 7, 2004, 7:27am UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/46 "2004-07-07T07:27:52Z")
> [@bouv](#): > > Sp if one managed to procure one of those deep-sea isopods and boil it, would you eat it? Probably, yes; it isn’t any uglier than a lobster or prawn, just _different_ (although it does have a malicious glint in its eye). It might not actually be edible though - some of these deep-water thingumajigs have nasty antifreeze - style chemicals in their bloodstream. ---
**Author:** ![clairobscur](https://avatars.discourse-cdn.com/v4/letter/c/839c29/32.png) [@clairobscur](https://boards.straightdope.com/u/clairobscur)\ **Post date:** [July 7, 2004, 8:01am UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/47 "2004-07-07T08:01:18Z")
> [@Ale](#): > > Please tell me those things never, **EVER** get out of their abysal dwellings. :eek: Sorry, but it’s mentionned on the page that they can colonize freshwaters… ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [July 7, 2004, 8:08am UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/48 "2004-07-07T08:08:45Z")
They’re _coming_… ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [July 7, 2004, 12:36pm UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/49 "2004-07-07T12:36:30Z")
> [@clairobscur](#): > > Sorry, but it’s mentionned on the page that they can colonize freshwaters… Ack! so now I think I know [what was that](http://boards.straightdope.com/sdmb/showthread.php?t=258660) . **RUN AWAY FROM THE HILLS!!!** … RUN AWAY FROM THE HILLS!!!.. RUN AWAY FROM THE HILLS!!! ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [July 7, 2004, 12:47pm UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/50 "2004-07-07T12:47:35Z")
[Aaaaaargh!](http://www.brookdalecc.edu/staff/sandyhook/taxonomy/crustaceans/isopodgiant.jpg) get it away from my face! ---
**Author:** ![Testy](https://avatars.discourse-cdn.com/v4/letter/t/c37758/32.png) [@Testy](https://boards.straightdope.com/u/Testy)\ **Post date:** [July 7, 2004, 1:22pm UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/51 "2004-07-07T13:22:16Z")
I particularly like this part of the reference: “_Some groups are parasitic and some travel in large groups at night._” So, there are **packs** of these things creeping around? Gaaak! Testy ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [July 7, 2004, 7:03pm UTC](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566/52 "2004-07-07T19:03:53Z")
> [@Colibri](#): > > And what, pray tell, is the legal definition of an “animal,” or an “insect?” An animal is that which is protected by the statutes covering cruelty to animals. An insect, presumably, is that which is not, and yet is also not a human being. It may be covered by other statutes, regulations, and/or treaties in force. Any other glib questions? [Previous page](https://boards.straightdope.com/t/is-a-lobster-an-insect/253566.md?page=2)