An article in the A^2 News today said a freak snowstorm in central Mexico is
killing millions of Monarch Butterflies.  This will undoubtedly affect the
number that we see next summer.  (They said up to 1/3 of the 12 million will
die from the snows today).

18 responses total.

Ow. Snow in central *Mexico*?! That would cause havoc, except in the mtns.

The butterfly haven is in the mountains - I don't know the altitude, but it
is where a certain species of tree exists that supports the Monarch.

Oh.  Well snow is at least possible in the mountains. At the high altitudes
even common.

I think it is more complicated. I recall that it takes several
*generations* for the Monarchs to migrate to those sites in Mexico,
and in the course of that, the eggs overwinter. The reverse is also
true, so we should not see a reduction in Monarch butterflies next
summer. Then again, my memory may be faulty...now, where is that
issue of Natural History....

I will try to find the newspaper article, it didn't say too much, but I
thought it suggested they make the entire flight each year.  

On a Balloon ride a few summers back, we were up around 500 ft (?) or so and
there was a steady stream of Monarchs flying by.  They were traveling in
pretty much straight lines and moving surprisingly fast.  There was no hint
of them from the ground.  When we landed at sundown, they were settling into
the tops of very tall oak trees for the night.

ps:  welcome back, Rane.

Here's an excerpt from an antique Funk & Wagnalls Encyclopedia:
     "Each fall the monarch migrates south in large numbers.  The longest
      flight known for a tagged adult is some 2900 km (about 1800 mi)
      from Ontario to Mexico.  Migratory groups congregate at the same 
      places each wnter, such as Pacific Grove, Calif. or the mountains,
      in central Mexico, where the trees may be completely covered with
      monarchs.  In the two-year lifetime of most butterflies, the 
      individual makes the trip twice."

I *think* almost all of the Monarchs alive in north America at the 
end of the summer make the migration south each year, and virtually 
the entire summer population of Monarchs in the US and Canada is 
descended from the ones that return north in the spring.  There may 
be, as Rane mentioned, more than one generation (they're called 
"broods") each summer, especially in the south where the summer is 
longer.  But all of the remaining living Monarchs, of whichever 
brood, migrate south at the end of each summer.  

Their winter haven was unknown for many years, and was only 
discovered twenty-five or so years ago.  I'm not sure if it's 
understood why this particular hill attracts them.  They don't feed 
on the trees, or anything like that.  Agricultural development has 
been encroaching on the hill, and it's possible the environment 
will eventually be destroyed anyway.  

I hope the Monarch isn't like the Passenger Pigeon -- ie, a species 
able to survive only in the millions.  If it is, it's because of 
its migratory habit, which decimates the population and weakens the 
survivors each year, and which needs a huge number of offspring to 
survive to reproductive age.  The Monarch's celebrated poisonous 
body fluids and warning-flag wings give it a predator-proof edge 
the Passenger Pigeon never had, however.  Who knows?  

It sort of looks like some US areas will be sans Monarchs next year.

Did you know about the butterfly (I think it is a viceroy) who looks almost
like a monarch and enjoys the lack of predators because of it's mimicry? 
Pretty neat trick.

On the ABC Evening News they said that 20 million Monarchs have died and the
species may be in jeopardy depending on how successfull the next breeding
seasons are.  

I wonder if there are any eggs and/or pupae which could survive the freeze?

It seems awfully unlikely to me that the Monarch species (which is 
called _Danaus plexippus_, btw) hasn't survived even worse winters in 
the past.  The only thing different this time is that now we know 
where they overwinter, so we're seeing it happen.  There have been 
dramatic ups and downs in the Monarch population in the past, no doubt 
due to similar natural events.  

Here's a story about how ubiquitous and resourceful Monarchs and their 
larval foodplant are.  We have a tall evergreen shrub in front of our 
house that's hollow inside, only we didn't know it until last summer 
when I noticed what looked like the head of a milkweed plant 
protruding from the top.  When I got up on a ladder and looked down 
inside the opening at the top of the shrub, I saw that there were 
several milkweed plants, or shoots, in there.  Some were trying to 
poke their way out the sides of the shrub, which they eventually 
succeeded in doing, and two of them had grown straight up to a height 
of nine+ feet and were emerging from the top of the shrub.  As far as 
I know, this was the only milkweed plant in the neighborhood.  I left 
it there, just to see what would happen, and, sure enough, we were 
soon seeing female Monarch butterflies around it.  Of all the weeds 
that could've taken root inside the shrub, the milkweed is the one 
that succeeded; and somehow, hidden though the plant was, female 
Monarchs found it and laid their eggs on it.  

Re the Viceroy, it's a famous example of mimicry, where a good-tasting 
butterfly evolves to resemble a bad-tasting one in order to fool 
predators.

The Monarch contains substances called cardiac glycosides, which it 
gets from its larval food plant, milkweed, and which cause 
instantaneous nausea when ingested.  Somewhere I have an issue of the 
Journal of the Lepidopterist Society with an article showing pictures 
of a young blue jay eating a Monarch and then blowing Monarch chunks 
all over its cage.  A bird samples Monarchs once and then no more.  

I've often wondered what kind of an advantage it can give a species 
when a predator has to actually eat you before it leaves your siblings 
alone, and where predators are as numerous as you are -- not to 
mention that at least one nonpoisonous species of butterfly has 
evolved to look exactly like you.  (What if the blue jay eats a tasty 
Viceroy first, instead of your brother?  Not only does that not 
protect you, it actually makes it worse for you.)  But I guess common 
sense says it *must* be better to taste awful than to taste good.  

The Monarch's orange and black coloring is common among insects that 
feed on milkweed, including bugs, beetles and other butterflies.  

The out of place word is "you". It doesn't matter if a trait makes it
worse for *you*, so long as it makes it better for the species. In
this case, the predators may well eat many individuals (including *you*),
but the result is a lessened predation on the species. 

An interesting point was raised however - this does not work too well
when the predators are more numerous than the prey species. However 
it is the reverse between birds and monarchs. A female birds lays
a few eggs per season; a female butterfly hundreds. In fact, the high
productivity fits right in with the poison defense: lots of untasty
morsels to train the predators. 

It is also interesting to speculate whether a bird eating a viceroy first
is likely to sample more than one monarch (or viceroy) thereafter? If
not, then there is no effect; if yes, predation is somewhat enhanced,
but so long as not too enhanced, the species remains with greater
protection.

md:  good point about probably being worse winters before.  It has not been
that many years since they knew the wintering location.

In fact, the robustness of the species may depend upon irregular mass
killings by frost. It removes those whose antifreeze has become too weak
by genetic drift, leaving more resistant individuals to continue a healthy
population. 

So far I have not seen any Monarch butterflies.  We have plenty of milkweed
nearby and they don't have any Monarch caterpillars on them yet either. 

We saw Monarchs in Macinac County in mid June, but the milkweeds were
only a foot high, and we saw no eggs. 

I saw a Monarch at the pond in our backyard Sunday afternoon. 

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