DR. JAMES ADAMS
JADAMS at em.daltonstate.edu
Thu Apr 6 12:54:48 EDT 2000
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
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
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