Government views Monarch Butterfly Releases as a threat toWestern Milkweeds

Patrick Foley patfoley at
Wed Dec 12 16:43:20 EST 2001

Paul and all,

I don't take the threat of butterfly releases against threatened Asclepias
species seriously, but I do think simple optimistic analyses often miss potential

For example, it may well happen that predator-prey systems (eg Danaus-Asclepias)
are sometimes stabilized by the patchy distributions of the prey and predators
(See Michael Hassell's new book on parasitoid-host population dynamics for some
evidence of this, or any ecology textbook). This is sometimes characterized as
prey escape in space. If human interference leads to more homogeneous
distributions of predators (monarchs), the odd Milkweed refugia may fail to

Now I doubt that the present level of Monarch releases puts such a system at
threat. I pose this example as just one problem release proponents have not even
considered. There may well be other problems I am incapable of imagining.

Most scientists recognize the limitations of their knowledge and imaginations.
This makes them wary of claims that disturbing ecosystems is safe. We have seen
too many cheerful human interferences come back to bite us. It is possible that
most ecologists lean towards the better safe than sorry, but so did our mothers.
We leave it to boosters, politicians and other trustworthy folk to set us

Scientists are not in a cabal to frustrate children or wedding planners. In fact
scientists, including myself have recommended less disturbing alternatives to
extra-natural releases including local releases of locally raised butterflies.
Moreover, most scientists don't have the time to argue about these issues. I am
stuck at the desk grading papers this week. Lucky you.

Patrick Foley
patfoley at

Paul Cherubini wrote:

> Bob Kriegel wrote:
> > If monarchs don't use the species in question as hosts or rarely use them
> > the proposed regulations will not do anything to protect those plants.
> > Period.   If monarch larvae do feed on the plants but do not kill them or
> > reduce their long term viability then they are also of no danger to the
> > plants.  If someone knows the answers to these two questions please speak
> > up.
> Do we really need to spend years of time and hundreds of thousands
> of dollars trying to answer these questions in order to determine if
> monarch releases are a danger to rare milkweed plants?
> Several years ago some commercial monarch breeders made the claim that
> releasing monarchs was good for conservation because it increased the size
> of wild monarch populations.  Immediately the academic community pointed
> out how flawed this claim was based on simple mathematical models.
> Now we are faced with a situation in which members the academic community
> (Dr. Karen Oberhauser, Dr. Chip Taylor and Dr Wayne F. Wehling of
> the USDA) are suggesting that research needs to be conducted to determine
> if releasing monarchs could kill or reduce the long term viability of certain
> rare milkweed plants.
> Now how come we don't see voices from the academic community immediately
> suggesting that we examine the legitimacy of these concerns using simple
> mathematical models?
> Example:
> Approximately 200,000 monarch butterflies are shipped interstate to all
> parts of the USA each year by butterfly breeders. The number of monarchs
> shipped to an individual state roughly mirrors the human population
> of that state.  Thus in Arizona we have a human population of 4,200,000 vs a
> national human population of 270,000,000 = approximately 3,111 monarchs will
> potentially be shipped to Arizona for release, mostly during the period
> April to October = 444 monarchs per month for seven months.
> Now does it make any common sense to contemplate the potential
> impact of 444 monarchs shipped to Arizona every month against a background
> monarch population numbering in the tens to hundreds of thousands
> and a background population of queen butterflies numbering
> in the hundreds of thousands or a background population of milkweed bugs
> and other invertebrate herbivores of milkweeds numbering in the six or
> seven figures?
> Paul Cherubini
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