arctiids, etc.

Thu Apr 6 12:54:48 EDT 2000

Dear listers,

	There was a discussion about a week and a half ago about 
edibility of Tiger Moths.  As this is an area of semi-expertise of 
mine, I thought I might share some information on this topic, now 
that I seem to have a little time to discuss this.

	John Shuey mentioned that in Uxmal, Yucatan, that Kiskadees 
seemed not to even chase arctiids when they started flying.  He 
posed the question as to whether they were really that great at 
taxonomy, or whether the tiger moths emitted sounds that indicate 
their unpalatability.

	The answer is not a simple yes or no to either question.  Here's 
some of what *is* known.

	1.  Tiger moths are not *known* to emit sounds indicating 
distastefulness unless stimulated first -- they *will* emit sounds in 
response to bat echolocation, as well as handling, which would 
take care of both the nighttime and daytime predators.  But again, 
emitting sounds as they initiate flight is not apparently something 
that is widespread (though it certainly is a possibility for some 
species, as the family is very speciose in the neotropics and little 
is known about many of the species).

	2.  About the taxonomic capabilities of Kiskadees, I have a 
couple of comments.  I certainly can tell the difference in flight 
patterns of a number of different moths, and often can identify even 
the genus (if not the species) of moth while in flight.  (Don't believe 
me?  Ask Doug Yanega, he'll tell you.)  Indeed, many arctiids fly 
*very* differently than most noctuids, and certainly differently than 
geometrids; one group, the "ctenuchine" wasp-moths, are easily 
recognizable and should be even to birds. I'm sure John Shuey 
noticed this, and so have many others.  Interestingly, at least one 
experiment done with bats shows that bats simply fly by 
ctenuchines flying around at night, even without the ctenuchines 
emitting any kind of sound, which suggests that the *audible* flight 
signature of ctenuchines is so different that bats can tell just by 
listening and simply avoid these species. Still, not all arctiids have 
radically different flight patterns, and yet if Kiskadees never chase 
them, then they must be really good at discerning at least 

John Himmelman asked about palatability and bright/cryptic 
coloration.  I have some comments here as well.

	1.  Bright color and chemical protection do not *necessarily* go 
hand in hand, though there is a strong correlation.  Still, as we all 
know, brightly colored species may be "faking" it.  One other item 
that is often lost in discussion of aposematic/mimetic coloration, 
however, is the differential sensitivity of different predators to the 
chemical protection (which I will talk about again shortly in reponse 
to Gary Anweiler's comments).  As most of us certainly 
understand, *no* defensive mechanism works 100% of the time 
against 100% of the possible predators.

	2.  About the chemical protection of arctiids.  John Himmelman 
wrote that in his experience, many arctiid larvae eat foodplants that 
seem to have little in the way of protective chemicals that can be 
sequestered by the larvae.  Absolutely true.  However . . ., in the 
numerous studies done with tiger moths, it has been shown that 
many species can not only sequester toxins from foodplants, but 
can synthesize their own protective chemicals de novo.  Pretty 
impressive little beasts, those arctiids.

	3.  Back to the coloration.  Many arctiids have cryptic or 
disruptive coloration . . . on the forewings.  Even bad tasting 
species benefit from being hidden, 'cause you never know whether 
you're going to have to train the naive predator!  John Himmelman 
writes that the "Milkweed Tussock Moth gives out about as much 
warning, color-wise [it's gray] as a burnt out traffic light."  True, 
when it is just sitting there.  However, when handled, this Tiger 
Moth folds its wings above its head a curls it's *brightly colored 
orange-yellow" abdomen downward in an aposematic display, as 
well as *releasing* volatile (foul-smelling), bad-tasting (yes, from 
personal experience, believe it or not) fluid from prothoracic glands. 
These two behaviors, aposematic display and fluid/odor release, 
are *widespread* in the arctiids.  The idea, again, is to remain 
somewhat hidden until encountered, at which point you show off 
brightly colored hindwings, undersides, or abdomens while emitting 
noxious chemicals.  Of course, some species are brightly colored 
all over, advertising bad taste all the time.

	4.  One other point that needs not be lost in this discussion is 
the fact that adult arctiids also seem to have pretty tough 
integument (the same is true for Monarch butterflies), and seem to 
be able to survive significant manipulation.  So, a predator grabs a 
moth, and gets an audible warning, a visible warning, as well as a 
mouthful of obnoxious tasting, frothy goo.  Seems to work well 
enough that the moths typically get away from most daytime 

	5.  John Himmelman mentions being nocturnal having its 
advantages.  John, did you forget about bats?  However, as I 
mentioned above, the sound they emit is emitted in response to 
bat echolocation, so, like the bright coloration during the day, the 
sound advertises these moths bad taste to bats even before the 
bats are in direct contact with the moths.  Some experiments 
suggest that the sounds some arctiid species emit actually even 
jam the echolocatory signals, which would be particularly good 
protection.  Still, different species of arctiids emit signals with 
different acoustic signatures, and they don't have much of an ability 
to alter the signals, so in any given place in the tropics, with 
numerous arctiid species and numerous bats, clearly most species 
of arctiids are *not* going to be jamming all species of bats.

Gary Anweiler brought up that in Canada where he is, Eastern 
Phoebes seem to eat most arctiids with relative impunity.  A 
couple of salient points need to be brought up here, and I also need 
to ask Gary a question.

	1.  Remember that, as stated above, different predator species 
are going to have different sensitivities to protective chemicals (just 
look at the anteaters, for instance).  

	2.  As for the species Gary mentions the Phoebes eating, 
Spilosoma and Hypoprepia are *not* strongly chemically protected. 
 Spilosoma species are white without much in the way of *obvious 
warning coloration or behavior*.  Hypoprepia species, however, are 
typically reddish or yellowish, yet the larvae eat lichens, which may 
or may not have chemicals that can be sequestered, depending on 
the species of lichens.  Could very easily be that the Hypoprepia 
are perfectly edible in Alberta.  As for the Grammia, however, I 
must admit I am a little surprised at the Phoebes eating these 
species.  They typically have great warning coloration (shown off 
during display) and the ability to synthesize at least some 
protective chemicals and release copious amounts of fluid from the 
prothoracic glands (though I have seen both scorpions and 
Calosoma ground beetles eating Grammia species).

	My questions for Gary:
	1.  Which species of Grammia are we talking about?

	2.  Did the birds eat the *entire* moth, or was there some 
selective "picking apart" of the moths before consumption.

	As for the effectiveness of warning coloration, remember that it 
only works if there is something *bad* to advertise.  It could simply 
be that the species Gary is talking about, in the *area* that he is 
talking about, simply are not well chemically protected.  The birds 
taste buds are fine; there probably simply isn't anything terribly bad 
to taste.  Remember, some of the northern Milkweed species 
apparently don't have a lot of secondary phytochemicals to 
sequester, so those Monarchs whose larvae mature on these 
species in the summer are often quite palatable to birds.

	All for now.


Dr. James K. Adams
Dept. of Natural Science and Math
Dalton State College
213 N. College Drive
Dalton, GA  30720
Phone: (706)272-4427; fax: (706)272-2533
U of Michigan's President James Angell's 
  Secret of Success: "Grow antennae, not horns"

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