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>> That was a great explanation for the basis of
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Very informative=2C Steve. Thanks.
Angus
=20
> Date: Mon=2C 19 Aug 2013 16:10:46 -0300
> From: srshaw@dal.ca
> To: naturens@chebucto.ns.ca
> Subject: RE: [NatureNS] caterpillar question- tuft control? (long=2C sorr=
y)
>=20
> Hi Angus=2C
> On part (1) below=2C you gave up too easily and obviously need to think=20
> more like a caterpillar. I used to rear a few species (mostly moths)=20
> as a kid in the UK and encountered the following defensive reactions=2C=20
> at least when I went near caterpillars or tried to touch them (might=20
> vary if the approach was from a wasp=2C and obviously wasps aren't the=20
> only things that eat caterpillars=2C either).
>=20
> - drop like a stone off a leaf or stem on to the undergrowth or soil=20
> below=2C making itself difficult to find=3B climb back up later (some=20
> noctuids would do this).
> - curl up into a millipede-like tight circle with defensive bristles=20
> sticking out=2C that may be noxious to some predators=2C or make=20
> parasitoids harder to gain a close approach to oviposit. Some tiger=20
> moths (arctiids) do this. Somebody is going to ask why the nasty=20
> irritating hairs break off so easily and I don't know=2C but presumably=20
> there's a weak spot near the base that's responsible. 'Deliberately'=20
> weakened areas underlie defensive reactions called 'autotomy'=20
> elsewhere=2C as when a crab defensively sheds a leg at the leg's=20
> specialized autotomy zone.
> - regurgitate noxious fluid from the mouthparts=2C that may smell bad=20
> and deter some attackers=2C suggesting a potentially unpleasant meal if=20
> pursued. This would be more common in insects like grasshoppers.
> - defensive writhing of the back end with the prolegs still attached=20
> to a stem=2C presumably in an attempt to prevent the predator or=20
> parasitoid gaining a foothold. I've seen a sphinx caterpillar here do=20
> this.
> - defensive front-end rearing to show fearsomely threatening eyespots=20
> - large elephant hawk moth caterpillars in UK do this (Deiliphilia=20
> elpenor=2C spelling from memory).
> - defensive rearing or writhing to remind predator of warning=20
> coloration that advertizes toxicity: orange-black banded cinnabar moth=20
> caterpillars (an arctiid? - I can't remember) that live in small=20
> colonies on ragwort do this. I was once involved in breeding these en=20
> masse for pocket money=2C in an ill- conceived scheme to export pupae to=
=20
> Australia to control invasive ragwort=2C bad for livestock. Apparently=20
> someone forgot that the seasons are 6 months out of sync so the adult=20
> moths emerged in winter.
>=20
> No doubt the lep specialists here or others can add a few more tricks?
>=20
> Re. damned if you do or don't=2C biologists view these sorts of=20
> adaptations as evolutionary 'arms races'. The prey species evolves a=20
> new or modified defense=2C then the predator evolves a countermeasure=3B=
=20
> well known in plants too. Usually=2C neither strategy is perfect so an=20
> equilibrium prevails for a while: sometimes a defense succeeds and=20
> sometimes it fails.
>=20
> On (2)=2C as you may know=2C one of the largest groups of brachyceran=20
> flies=2C tachinids=2C reproduce almost exclusively by parasitizing other=
=20
> insects either in the adult or larval state. They lay one or more=20
> eggs on the body of the insect host and the fly larvae slowly eat it=20
> up from the inside and then pupate=2C a pretty gruesome fate.
> A question is=2C how do they locate the host? There are a couple of=20
> genera of tachinids=2C one of which is a yellowish nondescript fly=20
> Ormia=2C that home in on singing male crickets=2C as you say. According=20
> to work done in Ron Hoy's lab in Cornell Univ=2C the fly shows quite=20
> exceptional directional selectivity of around 1=B0=2C so can=20
> accurately/quickly locate the sound source at night. Interest in this=20
> is that flies generally do not possess eardrums (tympana). This genus=20
> has evolved a pair of these on its 'chest' (ventral thorax) from=20
> pre-existing chordotonal organs there=2C that in other species respond=20
> just to internal stretch (this reprises an earlier comment about=20
> evolutionary adaptations usually being based on pre-existing=20
> structures).
>=20
> The main scientific interest is that the system is seemingly far too=20
> small to work at all acoustically=2C because the two tympana appear to=20
> be too small and too close together to allow either a significant=20
> sound intensity difference between them=2C or a significant sound time=20
> delay (in humans=2C directional hearing works because of sound-shadowing=
=20
> by the head at the frequencies we resolve=2C which generates a sound=20
> intensity difference between the eardrums=2C and there's also a time=20
> delay from most positions of the sound source because of the large=20
> distance between the ears). These crickets sing dominantly at ~6 kHz=20
> (from memory) where the sound wavelength is ~60 mm=2C while the=20
> separation of tympana is less than 1 mm (from memory). Daniel Robert=20
> originally in Hoy's lab came up with an explanation for how it works=2C=20
> involving coupling between the two tympana* via some fancy chitinous=20
> rods that amplify the sound delay=2C such that the fly can respond to=20
> time differences (that indicate direction)=2C in the nanosecond range.=20
> It's quite a challenging system to understand=2C technically.
> Steve (Halifax)
> *P.S.
> tympanum=2C eardrum (tympana =3D plural=3B Latin noun=2C neutral gender) =
=3D OK
> tympani=2C orchestral drums (plural only used=2C italian noun) =3D OK=2C =
but not here
> tympanae =3D hypothetical but non-existent plural Latin noun=2C female ge=
nder
> Steve (Hfx)
>=20
> Quoting Angus MacLean <cold_mac@hotmail.com>:
>=20
> > (1) Steve speaks of the caterpillar's defensive reaction to a=20
> > predator being nearby. So I'm thinking=2C what defensive reaction=20
> > would a caterpillar enable to avoid a wasp? ...hmm there's a leaf I=20
> > could hide under..shouldn't take me more than five mins to get=20
> > there!! However since they've evolved the detection device=2C there=20
> > must be more immediate steps they can take. (perhaps lay on their=20
> > back?).
> >
> >
> >
> > (2) Speaking of such things like tympanae=2C I read recently that=20
> > certain flies that prey on orthoptera use similar adaptations to=20
> > home in on the specific species they will parasitize. So like many=20
> > things in nature=2C you're dammed if you do (vocalize) & dammed if you=
=20
> > don't.
> >
> > Angus
> >
> >
> >
> > Date: Sun=2C 18 Aug 2013 18:16:28 -0300
> >> Subject: Re: [NatureNS] caterpillar question- tuft control? (long=2C s=
orry)
> >> From: nancypdowd@gmail.com
> >> To: naturens@chebucto.ns.ca
> >>
> >> Thank you Steve!!!!!!
> >>
> >> That was a great explanation for the basis of the caterpillar's tuft
> >> movements but also for a whole lot of things- such as the perfectly
> >> preserved hairs etc on insect exuviae (that I see when I hold my
> >> Cicada skin up to the light).
> >>
> >> Neat how Crickets and others triangulate with their tympanae to hone
> >> in on their calling mates.
> >>
> >> Nancy
> >>
> >> On Sun=2C Aug 18=2C 2013 at 3:22 PM=2C Stephen R. Shaw <srshaw@dal.ca>=
wrote:
> >> > Don't know who wrote the second paragraph quoted by Rick but it is o=
nly
> >> > partly correct. All of all parts of insect hairs are modified=20
> >> extensions of
> >> > the insect's exoskeleton (the cuticle) and all are therefore
> >> > 'cuticularized'. Cuticle is basically a matrix made of a complex
> >> > polysaccharide chitin plus other chemicals=2C and comes in a=20
> >> variety of forms=2C
> >> > from some that are hard and very stiff (the hard bits) and some very=
soft
> >> > and flexible (for instance=2C the inter-segmental membranes of the=20
> >> abdomens in
> >> > insects that allow a huge extension of the abdomen to oviposit in so=
il or
> >> > sand=2C as locusts do). Where the hairs bend=2C at their bases=2C th=
e cuticle is
> >> > much thinner=2C allowing more flexibility.
> >> >
> >> > Hairs in insects are generally classified as microtrichia and=20
> >> macrotrichia.
> >> > The former are small simple extensions of the surface cuticle=2C are=
not
> >> > hollow=2C have no associated nerve cell and don't do much that's kno=
wn. The
> >> > latter are larger=2C longer=2C often hollow. The type under discussi=
on on
> >> > caterpillars usually act as single mechanoreceptors connected to=20
> >> the central
> >> > nervous system (CNS)=2C because they are associated with a single bi=
polar (=3D
> >> > 'has 2 processes') nerve cell. The dendrite (outer process) of this =
cell
> >> > has specialized membrane channels that are sensitive to mechanical
> >> > deformation when the hair and the dendrite inserted in it are bent i=
n a
> >> > particular direction=2C but often not in other directions=2C so the=
=20
> >> CNS can tell
> >> > from which direction a deflection has come. This triggers nerve=20
> >> impulses in
> >> > the second process=2C the centrally directed nerve axon that ends=20
> >> up reaching
> >> > one of the 'ganglia' (nerve centres=2C like little brains) of the ve=
ntral
> >> > nerve cord (=3D part of the CNS). Insects in early evolution=20
> >> developed upside
> >> > down from vertebrates=2C so the nerve cord is on the ventral side=20
> >> of the body=2C
> >> > versus dorsal for vertebrates (=3D the spinal cord). The tormogen
> >> > and trichogen cells around each hair mechanoreceptor are specialized
> >> > support cells that modify the local environment for the bipolar neur=
on.
> >> >
> >> > None of these hairs have direct muscle insertions upon them=2C so wh=
en the
> >> > hairs move it is because the local body muscles nearby are deforming=
the
> >> > head end=2C the body surface=2C etc. The tufts of hairs move because=
they are
> >> > mechanically connected to local body movement=2C by virtue of being=
=20
> >> carried on
> >> > the body's exoskeleton or an appendage.
> >> >
> >> > Some of the directionally selective hairs are used to detect the clo=
se
> >> > approach of predators/parasites. When a disturbance of the air is=20
> >> generated
> >> > from a vibrating source like the wing beats of a wasp (colloquially =
called
> >> > 'sound' if the frequency is high enough for us to hear=2C but not to=
o high)=2C
> >> > two types of usable information result. The first is effective only =
very
> >> > close in=2C a so- called 'near-field effect' by which the local air=
=20
> >> molecules
> >> > incur large displacements. Hairs of the properly 'tuned' length for =
the
> >> > particular frequency can couple effectively to the displacement and =
get
> >> > stimulated=2C and so tell the caterpillar that a predator is=20
> >> hovering nearby=2C
> >> > which may lead to defensive reaction. This near field effect dissipa=
tes
> >> > very rapidly with distance away from the source=2C and is useless on=
ly a few
> >> > wavelengths away.
> >> >
> >> > The second effect also dissipates with distance but less severely (i=
nverse
> >> > square law to be specific)=2C so can be detected usefully at some=20
> >> distance. It
> >> > consists of propagated waves of compression and rarefaction of the a=
ir
> >> > molecules which we hear as sound=2C but to which the hairs do not re=
spond at
> >> > all. To hear that=2C you need a pressure-gradient detector like your
> >> > tympanum=2C but some insects also have them=2C like mantids=2C crick=
ets and also
> >> > katydids=2C which have the most complex acoustic inputs known. In Na=
ncy's
> >> > recent katydid=2C the main tympanum can be seen as the dark=20
> >> elliptical area on
> >> > the inside edge in the yellowish zone just below the 'knee'=2C on=20
> >> the tibia of
> >> > the front legs=2C in her nice second photo:
> >> >
> >> > http://www.flickr.com/photos/92981528@N08/9526735582/
> >> >
> >> > We have started to hear crickets sing in the last week or two. In so=
me
> >> > species=2C female crickets compare the sound intensity of the male=20
> >> song at the
> >> > two tympana on their front legs as a pressure difference=2C and use =
this
> >> > difference to locate the male by zig-zag walking towards him.
> >> >
> >> > Agreed that one should not 'underestimate the power of natural selec=
tion'
> >> > but I'd disagree that 'it just might happen'=2C if this is meant to=
=20
> >> imply that
> >> > anything could happen: not so. Evolutionary modification only=20
> >> works on what
> >> > went before it in that species line=2C therefore the range of possib=
ilities
> >> > for change=2C while large=2C is limited and rather narrowly channell=
ed. For
> >> > instance=2C tympanic ears above have evolved independently at least =
14 times
> >> > at last count in insects=2C on different parts of the body=2C but al=
l versions
> >> > are based on the chordotonal receptor=2C a pre-existing mechanorecep=
tor cell
> >> > complex that is found throughout the body and that monitors its inte=
rnal
> >> > state.
> >> >
> >> > Steve (Halifax)
> >> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> >
> >> >
> >> > Quoting Rick Whitman <dendroica.caerulescens@gmail.com>:
> >> >
> >> >> From wikipedia=2C from which all good things come:
> >> >> "The larvae <http://en.wikipedia.org/wiki/Larva> are brightly colou=
red=2C
> >> >> with tufts of hair-like setae <http://en.wikipedia.org/wiki/Setae>.=
"
> >> >>
> >> >> "Setae in entomology <http://en.wikipedia.org/wiki/Entomology> are =
often
> >> >> called hairs or chaetae <http://en.wikipedia.org/wiki/Chaeta>. They=
are
> >> >> unicellular and formed by the outgrowth of a single epidermal cell
> >> >> (trichogen). They are generally hollow and project through a second=
ary or
> >> >> accessory (tormogen) cell as it develops. The setal membrane is not
> >> >> cuticularized and movement is possible. This serves to protect the =
body."
> >> >>
> >> >>
> >> >> On Sat=2C Aug 17=2C 2013 at 7:30 PM=2C Rick Whitman <
> >> >> dendroica.caerulescens@gmail.com> wrote:
> >> >>
> >> >>> I feel that you are under-estimating the power of natural selectio=
n i.e.
> >> >>> if it benefits the organism=2C in terms of survival=2C it just mig=
ht happen.
> >> >>> I'm confident they are nothing more than highly evolved=20
> >> "hairs"=2C that can
> >> >>> be moved in a defensive manner.
> >> >>> Best=2C Rick.
> >> >>>
> >> >>>
> >> >>> On Sat=2C Aug 17=2C 2013 at 6:41 PM=2C nancy dowd=20
> >> <nancypdowd@gmail.com> wrote:
> >> >>>
> >> >>>> A week ago I took a picture of this fast-moving and impressive=2C=
albeit
> >> >>>> common=2C White-Marked Tussock Moth Caterpillar (Orgyia leucostig=
ma).
> >> >>>> Pls correct the ID if wrong:
> >> >>>> http://www.flickr.com/photos/92981528@N08/9501075283/
> >> >>>>
> >> >>>> Then it reared its head up at me and waved its front tufts in the=
air.
> >> >>>> Closeup of front end here:
> >> >>>> http://www.flickr.com/photos/92981528@N08/9503879386/
> >> >>>> Details are in photo captions.
> >> >>>>
> >> >>>> I thought caterpillar tufts and hairs were passive structures=2C =
moving
> >> >>>> only as the body moves. But they must have muscle control to wave
> >> >>>> independently of one another like that. Are they a modified anten=
nae
> >> >>>> or leg or? Can't find anything out searching the internet or in t=
he
> >> >>>> books I have so I will try here.
> >> >>>>
> >> >>>> Nancy
> >> >>> --
> >> >>> Rick Whitman
> >> >>>
>=20
=
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<body class=3D'hmmessage'><div dir=3D'ltr'>Very informative=2C Steve. Thank=
s.<BR>
Angus<BR> =3B<BR>
<DIV>>=3B Date: Mon=2C 19 Aug 2013 16:10:46 -0300<BR>>=3B From: srshaw@=
dal.ca<BR>>=3B To: naturens@chebucto.ns.ca<BR>>=3B Subject: RE: [Nature=
NS] caterpillar question- tuft control? (long=2C sorry)<BR>>=3B <BR>>=
=3B Hi Angus=2C<BR>>=3B On part (1) below=2C you gave up too easily and o=
bviously need to think <BR>>=3B more like a caterpillar. I used to rear a=
few species (mostly moths) <BR>>=3B as a kid in the UK and encountered t=
he following defensive reactions=2C <BR>>=3B at least when I went near ca=
terpillars or tried to touch them (might <BR>>=3B vary if the approach wa=
s from a wasp=2C and obviously wasps aren't the <BR>>=3B only things that=
eat caterpillars=2C either).<BR>>=3B <BR>>=3B - drop like a stone off =
a leaf or stem on to the undergrowth or soil <BR>>=3B below=2C making its=
elf difficult to find=3B climb back up later (some <BR>>=3B noctuids woul=
d do this).<BR>>=3B - curl up into a millipede-like tight circle with def=
ensive bristles <BR>>=3B sticking out=2C that may be noxious to some pred=
ators=2C or make <BR>>=3B parasitoids harder to gain a close approach to =
oviposit. Some tiger <BR>>=3B moths (arctiids) do this. Somebody is going=
to ask why the nasty <BR>>=3B irritating hairs break off so easily and I=
don't know=2C but presumably <BR>>=3B there's a weak spot near the base =
that's responsible. 'Deliberately' <BR>>=3B weakened areas underlie defen=
sive reactions called 'autotomy' <BR>>=3B elsewhere=2C as when a crab def=
ensively sheds a leg at the leg's <BR>>=3B specialized autotomy zone.<BR>=
>=3B - regurgitate noxious fluid from the mouthparts=2C that may smell ba=
d <BR>>=3B and deter some attackers=2C suggesting a potentially unpleasan=
t meal if <BR>>=3B pursued. This would be more common in insects like gra=
sshoppers.<BR>>=3B - defensive writhing of the back end with the prolegs =
still attached <BR>>=3B to a stem=2C presumably in an attempt to prevent =
the predator or <BR>>=3B parasitoid gaining a foothold. I've seen a sphin=
x caterpillar here do <BR>>=3B this.<BR>>=3B - defensive front-end rear=
ing to show fearsomely threatening eyespots <BR>>=3B - large elephant haw=
k moth caterpillars in UK do this (Deiliphilia <BR>>=3B elpenor=2C spelli=
ng from memory).<BR>>=3B - defensive rearing or writhing to remind predat=
or of warning <BR>>=3B coloration that advertizes toxicity: orange-black =
banded cinnabar moth <BR>>=3B caterpillars (an arctiid? - I can't remembe=
r) that live in small <BR>>=3B colonies on ragwort do this. I was once in=
volved in breeding these en <BR>>=3B masse for pocket money=2C in an ill-=
conceived scheme to export pupae to <BR>>=3B Australia to control invasi=
ve ragwort=2C bad for livestock. Apparently <BR>>=3B someone forgot that =
the seasons are 6 months out of sync so the adult <BR>>=3B moths emerged =
in winter.<BR>>=3B <BR>>=3B No doubt the lep specialists here or others=
can add a few more tricks?<BR>>=3B <BR>>=3B Re. damned if you do or do=
n't=2C biologists view these sorts of <BR>>=3B adaptations as evolutionar=
y 'arms races'. The prey species evolves a <BR>>=3B new or modified defen=
se=2C then the predator evolves a countermeasure=3B <BR>>=3B well known i=
n plants too. Usually=2C neither strategy is perfect so an <BR>>=3B equil=
ibrium prevails for a while: sometimes a defense succeeds and <BR>>=3B so=
metimes it fails.<BR>>=3B <BR>>=3B On (2)=2C as you may know=2C one of =
the largest groups of brachyceran <BR>>=3B flies=2C tachinids=2C reproduc=
e almost exclusively by parasitizing other <BR>>=3B insects either in the=
adult or larval state. They lay one or more <BR>>=3B eggs on the body of=
the insect host and the fly larvae slowly eat it <BR>>=3B up from the in=
side and then pupate=2C a pretty gruesome fate.<BR>>=3B A question is=2C =
how do they locate the host? There are a couple of <BR>>=3B genera of tac=
hinids=2C one of which is a yellowish nondescript fly <BR>>=3B Ormia=2C t=
hat home in on singing male crickets=2C as you say. According <BR>>=3B to=
work done in Ron Hoy's lab in Cornell Univ=2C the fly shows quite <BR>>=
=3B exceptional directional selectivity of around 1=B0=2C so can <BR>>=3B=
accurately/quickly locate the sound source at night. Interest in this <BR>=
>=3B is that flies generally do not possess eardrums (tympana). This genu=
s <BR>>=3B has evolved a pair of these on its 'chest' (ventral thorax) fr=
om <BR>>=3B pre-existing chordotonal organs there=2C that in other specie=
s respond <BR>>=3B just to internal stretch (this reprises an earlier com=
ment about <BR>>=3B evolutionary adaptations usually being based on pre-e=
xisting <BR>>=3B structures).<BR>>=3B <BR>>=3B The main scientific in=
terest is that the system is seemingly far too <BR>>=3B small to work at =
all acoustically=2C because the two tympana appear to <BR>>=3B be too sma=
ll and too close together to allow either a significant <BR>>=3B sound in=
tensity difference between them=2C or a significant sound time <BR>>=3B d=
elay (in humans=2C directional hearing works because of sound-shadowing <BR=
>>=3B by the head at the frequencies we resolve=2C which generates a soun=
d <BR>>=3B intensity difference between the eardrums=2C and there's also =
a time <BR>>=3B delay from most positions of the sound source because of =
the large <BR>>=3B distance between the ears). These crickets sing domina=
ntly at ~6 kHz <BR>>=3B (from memory) where the sound wavelength is ~60 m=
m=2C while the <BR>>=3B separation of tympana is less than 1 mm (from mem=
ory). Daniel Robert <BR>>=3B originally in Hoy's lab came up with an expl=
anation for how it works=2C <BR>>=3B involving coupling between the two t=
ympana* via some fancy chitinous <BR>>=3B rods that amplify the sound del=
ay=2C such that the fly can respond to <BR>>=3B time differences (that in=
dicate direction)=2C in the nanosecond range. <BR>>=3B It's quite a chall=
enging system to understand=2C technically.<BR>>=3B Steve (Halifax)<BR>&g=
t=3B *P.S.<BR>>=3B tympanum=2C eardrum (tympana =3D plural=3B Latin noun=
=2C neutral gender) =3D OK<BR>>=3B tympani=2C orchestral drums (plural on=
ly used=2C italian noun) =3D OK=2C but not here<BR>>=3B tympanae =3D hypo=
thetical but non-existent plural Latin noun=2C female gender<BR>>=3B Stev=
e (Hfx)<BR>>=3B <BR>>=3B Quoting Angus MacLean <=3Bcold_mac@hotmail.c=
om>=3B:<BR>>=3B <BR>>=3B >=3B (1) Steve speaks of the caterpillar's=
defensive reaction to a <BR>>=3B >=3B predator being nearby. So I'm th=
inking=2C what defensive reaction <BR>>=3B >=3B would a caterpillar ena=
ble to avoid a wasp? ...hmm there's a leaf I <BR>>=3B >=3B could hide u=
nder..shouldn't take me more than five mins to get <BR>>=3B >=3B there!=
! However since they've evolved the detection device=2C there <BR>>=3B &g=
t=3B must be more immediate steps they can take. (perhaps lay on their <BR>=
>=3B >=3B back?).<BR>>=3B >=3B<BR>>=3B >=3B<BR>>=3B >=3B<BR=
>>=3B >=3B (2) Speaking of such things like tympanae=2C I read recently=
that <BR>>=3B >=3B certain flies that prey on orthoptera use similar a=
daptations to <BR>>=3B >=3B home in on the specific species they will p=
arasitize. So like many <BR>>=3B >=3B things in nature=2C you're dammed=
if you do (vocalize) &=3B dammed if you <BR>>=3B >=3B don't.<BR>>=
=3B >=3B<BR>>=3B >=3B Angus<BR>>=3B >=3B<BR>>=3B >=3B<BR>>=
=3B >=3B<BR>>=3B >=3B Date: Sun=2C 18 Aug 2013 18:16:28 -0300<BR>>=
=3B >=3B>=3B Subject: Re: [NatureNS] caterpillar question- tuft control=
? (long=2C sorry)<BR>>=3B >=3B>=3B From: nancypdowd@gmail.com<BR>>=
=3B >=3B>=3B To: naturens@chebucto.ns.ca<BR>>=3B >=3B>=3B<BR>>=
=3B >=3B>=3B Thank you Steve!!!!!!<BR>>=3B >=3B>=3B<BR>>=3B >=
=3B>=3B That was a great explanation for the basis of the caterpillar's t=
uft<BR>>=3B >=3B>=3B movements but also for a whole lot of things- su=
ch as the perfectly<BR>>=3B >=3B>=3B preserved hairs etc on insect ex=
uviae (that I see when I hold my<BR>>=3B >=3B>=3B Cicada skin up to t=
he light).<BR>>=3B >=3B>=3B<BR>>=3B >=3B>=3B Neat how Crickets =
and others triangulate with their tympanae to hone<BR>>=3B >=3B>=3B i=
n on their calling mates.<BR>>=3B >=3B>=3B<BR>>=3B >=3B>=3B Nan=
cy<BR>>=3B >=3B>=3B<BR>>=3B >=3B>=3B On Sun=2C Aug 18=2C 2013 a=
t 3:22 PM=2C Stephen R. Shaw <=3Bsrshaw@dal.ca>=3B wrote:<BR>>=3B >=
=3B>=3B >=3B Don't know who wrote the second paragraph quoted by Rick b=
ut it is only<BR>>=3B >=3B>=3B >=3B partly correct. All of all part=
s of insect hairs are modified <BR>>=3B >=3B>=3B extensions of<BR>>=
=3B >=3B>=3B >=3B the insect's exoskeleton (the cuticle) and all are =
therefore<BR>>=3B >=3B>=3B >=3B 'cuticularized'. Cuticle is basical=
ly a matrix made of a complex<BR>>=3B >=3B>=3B >=3B polysaccharide =
chitin plus other chemicals=2C and comes in a <BR>>=3B >=3B>=3B varie=
ty of forms=2C<BR>>=3B >=3B>=3B >=3B from some that are hard and ve=
ry stiff (the hard bits) and some very soft<BR>>=3B >=3B>=3B >=3B a=
nd flexible (for instance=2C the inter-segmental membranes of the <BR>>=
=3B >=3B>=3B abdomens in<BR>>=3B >=3B>=3B >=3B insects that all=
ow a huge extension of the abdomen to oviposit in soil or<BR>>=3B >=3B&=
gt=3B >=3B sand=2C as locusts do). Where the hairs bend=2C at their bases=
=2C the cuticle is<BR>>=3B >=3B>=3B >=3B much thinner=2C allowing m=
ore flexibility.<BR>>=3B >=3B>=3B >=3B<BR>>=3B >=3B>=3B >=
=3B Hairs in insects are generally classified as microtrichia and <BR>>=
=3B >=3B>=3B macrotrichia.<BR>>=3B >=3B>=3B >=3B The former are=
small simple extensions of the surface cuticle=2C are not<BR>>=3B >=3B=
>=3B >=3B hollow=2C have no associated nerve cell and don't do much tha=
t's known. The<BR>>=3B >=3B>=3B >=3B latter are larger=2C longer=2C=
often hollow. The type under discussion on<BR>>=3B >=3B>=3B >=3B c=
aterpillars usually act as single mechanoreceptors connected to <BR>>=3B =
>=3B>=3B the central<BR>>=3B >=3B>=3B >=3B nervous system (CNS)=
=2C because they are associated with a single bipolar (=3D<BR>>=3B >=3B=
>=3B >=3B 'has 2 processes') nerve cell. The dendrite (outer process) o=
f this cell<BR>>=3B >=3B>=3B >=3B has specialized membrane channels=
that are sensitive to mechanical<BR>>=3B >=3B>=3B >=3B deformation=
when the hair and the dendrite inserted in it are bent in a<BR>>=3B >=
=3B>=3B >=3B particular direction=2C but often not in other directions=
=2C so the <BR>>=3B >=3B>=3B CNS can tell<BR>>=3B >=3B>=3B >=
=3B from which direction a deflection has come. This triggers nerve <BR>>=
=3B >=3B>=3B impulses in<BR>>=3B >=3B>=3B >=3B the second proce=
ss=2C the centrally directed nerve axon that ends <BR>>=3B >=3B>=3B u=
p reaching<BR>>=3B >=3B>=3B >=3B one of the 'ganglia' (nerve centre=
s=2C like little brains) of the ventral<BR>>=3B >=3B>=3B >=3B nerve=
cord (=3D part of the CNS). Insects in early evolution <BR>>=3B >=3B&g=
t=3B developed upside<BR>>=3B >=3B>=3B >=3B down from vertebrates=
=2C so the nerve cord is on the ventral side <BR>>=3B >=3B>=3B of the=
body=2C<BR>>=3B >=3B>=3B >=3B versus dorsal for vertebrates (=3D t=
he spinal cord). The tormogen<BR>>=3B >=3B>=3B >=3B and trichogen c=
ells around each hair mechanoreceptor are specialized<BR>>=3B >=3B>=
=3B >=3B support cells that modify the local environment for the bipolar =
neuron.<BR>>=3B >=3B>=3B >=3B<BR>>=3B >=3B>=3B >=3B None of=
these hairs have direct muscle insertions upon them=2C so when the<BR>>=
=3B >=3B>=3B >=3B hairs move it is because the local body muscles nea=
rby are deforming the<BR>>=3B >=3B>=3B >=3B head end=2C the body su=
rface=2C etc. The tufts of hairs move because they are<BR>>=3B >=3B>=
=3B >=3B mechanically connected to local body movement=2C by virtue of be=
ing <BR>>=3B >=3B>=3B carried on<BR>>=3B >=3B>=3B >=3B the bo=
dy's exoskeleton or an appendage.<BR>>=3B >=3B>=3B >=3B<BR>>=3B &=
gt=3B>=3B >=3B Some of the directionally selective hairs are used to de=
tect the close<BR>>=3B >=3B>=3B >=3B approach of predators/parasite=
s. When a disturbance of the air is <BR>>=3B >=3B>=3B generated<BR>&g=
t=3B >=3B>=3B >=3B from a vibrating source like the wing beats of a w=
asp (colloquially called<BR>>=3B >=3B>=3B >=3B 'sound' if the frequ=
ency is high enough for us to hear=2C but not too high)=2C<BR>>=3B >=3B=
>=3B >=3B two types of usable information result. The first is effectiv=
e only very<BR>>=3B >=3B>=3B >=3B close in=2C a so- called 'near-fi=
eld effect' by which the local air <BR>>=3B >=3B>=3B molecules<BR>>=
=3B >=3B>=3B >=3B incur large displacements. Hairs of the properly 't=
uned' length for the<BR>>=3B >=3B>=3B >=3B particular frequency can=
couple effectively to the displacement and get<BR>>=3B >=3B>=3B >=
=3B stimulated=2C and so tell the caterpillar that a predator is <BR>>=3B=
>=3B>=3B hovering nearby=2C<BR>>=3B >=3B>=3B >=3B which may le=
ad to defensive reaction. This near field effect dissipates<BR>>=3B >=
=3B>=3B >=3B very rapidly with distance away from the source=2C and is =
useless only a few<BR>>=3B >=3B>=3B >=3B wavelengths away.<BR>>=
=3B >=3B>=3B >=3B<BR>>=3B >=3B>=3B >=3B The second effect als=
o dissipates with distance but less severely (inverse<BR>>=3B >=3B>=
=3B >=3B square law to be specific)=2C so can be detected usefully at som=
e <BR>>=3B >=3B>=3B distance. It<BR>>=3B >=3B>=3B >=3B consis=
ts of propagated waves of compression and rarefaction of the air<BR>>=3B =
>=3B>=3B >=3B molecules which we hear as sound=2C but to which the ha=
irs do not respond at<BR>>=3B >=3B>=3B >=3B all. To hear that=2C yo=
u need a pressure-gradient detector like your<BR>>=3B >=3B>=3B >=3B=
tympanum=2C but some insects also have them=2C like mantids=2C crickets an=
d also<BR>>=3B >=3B>=3B >=3B katydids=2C which have the most comple=
x acoustic inputs known. In Nancy's<BR>>=3B >=3B>=3B >=3B recent ka=
tydid=2C the main tympanum can be seen as the dark <BR>>=3B >=3B>=3B =
elliptical area on<BR>>=3B >=3B>=3B >=3B the inside edge in the yel=
lowish zone just below the 'knee'=2C on <BR>>=3B >=3B>=3B the tibia o=
f<BR>>=3B >=3B>=3B >=3B the front legs=2C in her nice second photo:=
<BR>>=3B >=3B>=3B >=3B<BR>>=3B >=3B>=3B >=3B http://www.fli=
ckr.com/photos/92981528@N08/9526735582/<BR>>=3B >=3B>=3B >=3B<BR>&g=
t=3B >=3B>=3B >=3B We have started to hear crickets sing in the last =
week or two. In some<BR>>=3B >=3B>=3B >=3B species=2C female cricke=
ts compare the sound intensity of the male <BR>>=3B >=3B>=3B song at =
the<BR>>=3B >=3B>=3B >=3B two tympana on their front legs as a pres=
sure difference=2C and use this<BR>>=3B >=3B>=3B >=3B difference to=
locate the male by zig-zag walking towards him.<BR>>=3B >=3B>=3B >=
=3B<BR>>=3B >=3B>=3B >=3B Agreed that one should not 'underestimate=
the power of natural selection'<BR>>=3B >=3B>=3B >=3B but I'd disa=
gree that 'it just might happen'=2C if this is meant to <BR>>=3B >=3B&g=
t=3B imply that<BR>>=3B >=3B>=3B >=3B anything could happen: not so=
. Evolutionary modification only <BR>>=3B >=3B>=3B works on what<BR>&=
gt=3B >=3B>=3B >=3B went before it in that species line=2C therefore =
the range of possibilities<BR>>=3B >=3B>=3B >=3B for change=2C whil=
e large=2C is limited and rather narrowly channelled. For<BR>>=3B >=3B&=
gt=3B >=3B instance=2C tympanic ears above have evolved independently at =
least 14 times<BR>>=3B >=3B>=3B >=3B at last count in insects=2C on=
different parts of the body=2C but all versions<BR>>=3B >=3B>=3B >=
=3B are based on the chordotonal receptor=2C a pre-existing mechanoreceptor=
cell<BR>>=3B >=3B>=3B >=3B complex that is found throughout the bo=
dy and that monitors its internal<BR>>=3B >=3B>=3B >=3B state.<BR>&=
gt=3B >=3B>=3B >=3B<BR>>=3B >=3B>=3B >=3B Steve (Halifax)<BR>=
>=3B >=3B>=3B >=3B ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=
~~~<BR>>=3B >=3B>=3B >=3B<BR>>=3B >=3B>=3B >=3B<BR>>=3B &=
gt=3B>=3B >=3B Quoting Rick Whitman <=3Bdendroica.caerulescens@gmail.=
com>=3B:<BR>>=3B >=3B>=3B >=3B<BR>>=3B >=3B>=3B >=3B>=
=3B From wikipedia=2C from which all good things come:<BR>>=3B >=3B>=
=3B >=3B>=3B "The larvae <=3Bhttp://en.wikipedia.org/wiki/Larva>=3B=
are brightly coloured=2C<BR>>=3B >=3B>=3B >=3B>=3B with tufts of=
hair-like setae <=3Bhttp://en.wikipedia.org/wiki/Setae>=3B."<BR>>=3B=
>=3B>=3B >=3B>=3B<BR>>=3B >=3B>=3B >=3B>=3B "Setae in en=
tomology <=3Bhttp://en.wikipedia.org/wiki/Entomology>=3B are often<BR>&=
gt=3B >=3B>=3B >=3B>=3B called hairs or chaetae <=3Bhttp://en.wik=
ipedia.org/wiki/Chaeta>=3B. They are<BR>>=3B >=3B>=3B >=3B>=3B =
unicellular and formed by the outgrowth of a single epidermal cell<BR>>=
=3B >=3B>=3B >=3B>=3B (trichogen). They are generally hollow and pr=
oject through a secondary or<BR>>=3B >=3B>=3B >=3B>=3B accessory =
(tormogen) cell as it develops. The setal membrane is not<BR>>=3B >=3B&=
gt=3B >=3B>=3B cuticularized and movement is possible. This serves to p=
rotect the body."<BR>>=3B >=3B>=3B >=3B>=3B<BR>>=3B >=3B>=
=3B >=3B>=3B<BR>>=3B >=3B>=3B >=3B>=3B On Sat=2C Aug 17=2C 20=
13 at 7:30 PM=2C Rick Whitman <=3B<BR>>=3B >=3B>=3B >=3B>=3B de=
ndroica.caerulescens@gmail.com>=3B wrote:<BR>>=3B >=3B>=3B >=3B&g=
t=3B<BR>>=3B >=3B>=3B >=3B>=3B>=3B I feel that you are under-es=
timating the power of natural selection i.e.<BR>>=3B >=3B>=3B >=3B&=
gt=3B>=3B if it benefits the organism=2C in terms of survival=2C it just =
might happen.<BR>>=3B >=3B>=3B >=3B>=3B>=3B I'm confident they =
are nothing more than highly evolved <BR>>=3B >=3B>=3B "hairs"=2C tha=
t can<BR>>=3B >=3B>=3B >=3B>=3B>=3B be moved in a defensive man=
ner.<BR>>=3B >=3B>=3B >=3B>=3B>=3B Best=2C Rick.<BR>>=3B >=
=3B>=3B >=3B>=3B>=3B<BR>>=3B >=3B>=3B >=3B>=3B>=3B<BR>&=
gt=3B >=3B>=3B >=3B>=3B>=3B On Sat=2C Aug 17=2C 2013 at 6:41 PM=
=2C nancy dowd <BR>>=3B >=3B>=3B <=3Bnancypdowd@gmail.com>=3B wro=
te:<BR>>=3B >=3B>=3B >=3B>=3B>=3B<BR>>=3B >=3B>=3B >=3B=
>=3B>=3B>=3B A week ago I took a picture of this fast-moving and impr=
essive=2C albeit<BR>>=3B >=3B>=3B >=3B>=3B>=3B>=3B common=2C =
White-Marked Tussock Moth Caterpillar (Orgyia leucostigma).<BR>>=3B >=
=3B>=3B >=3B>=3B>=3B>=3B Pls correct the ID if wrong:<BR>>=3B &=
gt=3B>=3B >=3B>=3B>=3B>=3B http://www.flickr.com/photos/92981528@=
N08/9501075283/<BR>>=3B >=3B>=3B >=3B>=3B>=3B>=3B<BR>>=3B &=
gt=3B>=3B >=3B>=3B>=3B>=3B Then it reared its head up at me and w=
aved its front tufts in the air.<BR>>=3B >=3B>=3B >=3B>=3B>=3B&=
gt=3B Closeup of front end here:<BR>>=3B >=3B>=3B >=3B>=3B>=3B&=
gt=3B http://www.flickr.com/photos/92981528@N08/9503879386/<BR>>=3B >=
=3B>=3B >=3B>=3B>=3B>=3B Details are in photo captions.<BR>>=3B=
>=3B>=3B >=3B>=3B>=3B>=3B<BR>>=3B >=3B>=3B >=3B>=3B&=
gt=3B>=3B I thought caterpillar tufts and hairs were passive structures=
=2C moving<BR>>=3B >=3B>=3B >=3B>=3B>=3B>=3B only as the body=
moves. But they must have muscle control to wave<BR>>=3B >=3B>=3B &g=
t=3B>=3B>=3B>=3B independently of one another like that. Are they a m=
odified antennae<BR>>=3B >=3B>=3B >=3B>=3B>=3B>=3B or leg or?=
Can't find anything out searching the internet or in the<BR>>=3B >=3B&=
gt=3B >=3B>=3B>=3B>=3B books I have so I will try here.<BR>>=3B &=
gt=3B>=3B >=3B>=3B>=3B>=3B<BR>>=3B >=3B>=3B >=3B>=3B>=
=3B>=3B Nancy<BR>>=3B >=3B>=3B >=3B>=3B>=3B --<BR>>=3B >=
=3B>=3B >=3B>=3B>=3B Rick Whitman<BR>>=3B >=3B>=3B >=3B>=
=3B>=3B<BR>>=3B <BR></DIV> </div></body>
</html>=
--_24f919ce-8c44-46da-b42c-fc56dc71f9d0_--
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