The peppered moth is a temperate species
of night-flying moth. Peppered moth
evolution is an example of population
genetics and natural selection.
Description
The wingspan is 55mm. median It is
relatively stout-bodied, with forewings
relatively narrow-elongate. The wings
are white, "peppered" with black, and
with more or less distinct cross lines,
also black. The black speckling varies
in amount, in some examples it is almost
absent, whilst in others it is so dense
that the wings appear to be black
sprinkled with white. The antennae of
males are strongly bipectinate. 
Distribution
Biston betularia is found in China,
Russia, Mongolia, Japan, North Korea,
South Korea, Nepal, Kazakhstan,
Kirghizstan, Turkmenistan, Georgia,
Azerbaijan, Armenia, Europe and North
America.
Ecology and life cycle
In Britain and Ireland, the peppered
moth is univoltine, whilst in
south-eastern North America it is
bivoltine. The lepidopteran life cycle
consists of four stages: ova, several
larval instars, pupae, which overwinter
live in the soil, and imagines. During
the day, the moths typically rest on
trees, where they are preyed on by
birds.
The caterpillar is a twig mimic, varying
in colour between green and brown. On a
historical note, it was one of the first
animals to be identified as being
camouflaged with countershading to make
it appear flat, in a paper by Edward
Bagnall Poulton in 1887.
It goes into the soil late in the
season, where it pupates in order to
spend the winter. The imagines emerge
from the pupae between late May and
August, the males slightly before the
females. They emerge late in the day and
dry their wings before flying that
night.
The males fly every night of their lives
in search of females, whereas the
females only fly on the first night.
Thereafter, the females release
pheromones to attract males. Since the
pheromone is carried by the wind, males
tend to travel up the concentration
gradient, i.e., toward the source.
During flight, they are subject to
predation by bats. The males guard the
female from other males until she lays
the eggs. The female lays about 2,000
pale-green ovoid eggs about 1 mm in
length into crevices in bark with her
ovipositor.
= Resting behaviour=
A mating pair or a lone individual will
spend the day hiding from predators,
particularly birds. In the case of the
former, the male stays with the female
to ensure paternity. The best evidence
for resting positions is given by data
collected by the peppered moth
researcher Michael Majerus, and it is
given in the accompanying charts. These
data were originally published in
Howlett and Majerus, and an updated
version published in Majerus, who
concluded that the moths rest in the
upper part of the trees. Majerus notes:
Creationist critics of the peppered moth
have often pointed to a statement made
by Clarke et al.: "... In 25 years we
have only found two betularia on the
tree trunks or walls adjacent to our
traps, and none elsewhere". The reason
now seems obvious. Few people spend
their time looking for moths up in the
trees. That is where peppered moths rest
by day.
From their original data, Howlett and
Majerus concluded that peppered moths
generally rest in unexposed positions,
using three main types of site. Firstly,
a few inches below a branch-trunk joint
on a tree trunk where the moth is in
shadow; secondly, on the underside of
branches and thirdly on foliate twigs.
The above data would appear to support
this.
Further support for these resting
positions is given from experiments
watching captive moths taking up resting
positions in both males and females.
Majerus, et al., have shown that
peppered moths are cryptically
camouflaged against their backgrounds
when they rest in the boughs of trees.
It is clear that in human visible
wavelengths, typica are camouflaged
against lichens and carbonaria against
plain bark. However, birds are capable
of seeing ultraviolet light that humans
cannot see. Using an
ultraviolet-sensitive video camera,
Majerus et al. showed that typica
reflect ultraviolet light in a speckled
fashion and are camouflaged against
crustose lichens common on branches,
both in ultraviolet and human-visible
wavelengths. However, typica are not as
well camouflaged against foliose lichens
common on tree trunks; though they are
camouflaged in human wavelengths, in
ultraviolet wavelengths, foliose lichens
do not reflect ultraviolet light.
During an experiment in Cambridge over
the seven years 2001–2007 Majerus noted
the natural resting positions of
peppered moths, and of the 135 moths
examined over half were on tree
branches, mostly on the lower half of
the branch, 37% were on tree trunks,
mostly on the north side, and only 12.6%
were resting on or under twigs.
Polymorphism
= Introduction on Forms=
There are several melanic and
non-melanic morphs of the peppered moth.
These are controlled genetically. A
particular colour morph can be indicated
in a standard way by following the
species name in the form "morpha morph
name". The use of "form" in the method
of Biston betularia f. formname in
detailing these variations is also a
widespread practice.
These forms are often accidentally
elevated to subspecies status when they
appear in literature. Not adding the
"f." or morpha infers that the taxon is
a subspecies instead of a form, as in
Biston betularia carbonaria instead of
Biston betularia f. carbonaria. Rarely
forms have been elevated to species
status as in Biston carbonaria. Either
of these two circumstances might lead to
the erroneous belief that speciation was
involved in the observed evolution of
the peppered moth. This is not the case;
individuals of each morph interbreed and
produce fertile offspring with
individuals of all other morphs; hence
there is only one peppered moth species.
By contrast, different subspecies of the
same species can theoretically
interbreed with one another and will
produce fully fertile and healthy
offspring but in practice do not, as
they live in different regions or
reproduce in different seasons.
Full-fledged species are either unable
to produce fertile and healthy
offspring, or do not recognize each
other's courtship signals, or both.
European breeding experiments have shown
that in Biston betularia betularia, the
allele for melanism producing morpha
carbonaria is controlled by a single
locus. The melanic allele is dominant to
the non-melanic allele. This situation
is, however, somewhat complicated by the
presence of three other alleles that
produce indistinguishable morphs of
morpha medionigra. These are of
intermediate dominance, but this is not
complete.
= Form Names=
In continental Europe, there are three
morphs: the white morph typica, the dark
melanistic morph carbonaria, and an
intermediate form medionigra.
In Britain, the typical white morph is
known as typica, the melanic morph is
carbonaria, and the intermediate
phenotype is named insularia.
In North America, the melanic black
morph is morpha swettaria. In Biston
betularia cognataria, the melanic allele
is similarly dominant to the non-melanic
allele. There are also some intermediate
morphs. In Japan, no melanic morphs have
been recorded; they are all morpha
typica.
At present, the precise molecular
genetics and biochemistry of the
melanism in this species remains
unknown. True has reviewed this and
suggests work based on candidate genes
from other insects such as the fruit fly
Drosophila melanogaster. In any case, it
is rather likely that the underlying
mechanism is not overly complex and, as
indicated above, does not involve very
many genes and alleles: Unlike for
example the variation seen in human skin
color, Peppered Moth morphs are not
clinal and can generally be readily
distinguished from another.
Evolution
The evolution of the peppered moth over
the last two hundred years has been
studied in detail. At the start of this
period, the vast majority of peppered
moths had light coloured wing patterns
which effectively camouflaged them
against the light-coloured trees and
lichens upon which they rested. However,
due to widespread pollution during the
Industrial Revolution in England, many
of the lichens died out, and the trees
which peppered moths rested on became
blackened by soot, causing most of the
light-coloured moths, or typica, to die
off due to predation. At the same time,
the dark-coloured, or melanic, moths,
carbonaria, flourished because they
could hide on the darkened trees.
Since then, with improved environmental
standards, light-coloured peppered moths
have again become common, and the
dramatic change in the peppered moth's
population has remained a subject of
much interest and study. This has led to
the coining of the term "industrial
melanism" to refer to the genetic
darkening of species in response to
pollutants. As a result of the
relatively simple and easy-to-understand
circumstances of the adaptation, the
peppered moth has become a common
example used in explaining or
demonstrating natural selection to
laypeople and classroom students through
simulations.
The first carbonaria morph was recorded
by Edleston in Manchester in 1848, and
over the subsequent years it increased
in frequency. Predation experiments,
particularly by Bernard Kettlewell,
established that the agent of selection
was birds who preyed on the carbonaria
morph.
Jonathan Wells is one of a number of
creationists who have criticized the use
of peppered moth melanism as an example
of evolution in action. In his book
Icons of Evolution, Wells alleges that
peppered moth studies, and in particular
Kettlewell's experiments, were
erroneous. Similarly, in 2002 Judith
Hooper repeatedly implied fraud and
error in Kettlewell's experiments in her
book titled Of moths and men. Despite
some valid criticisms of the early
experiments, there has been no evidence
of fraud. Subsequent experiments and
observations have supported the initial
evolutionary explanation of the
phenomenon.
Gallery
References
External links
Bruce Grant has written several papers
on melanism in the peppered moth which
are listed on his home page.
Online lecture: "The rise and fall of
the melanic Peppered Moth" presented by
Laurence Cook.
Matt Young. "Moonshine: Why the Peppered
Moth remains an Icon of Evolution".
Department of Physics, Colorado School
of Mines. Retrieved 2009-01-03. 
The Peppered Moth: Decline of a
Darwinian Disciple. This is the
transcript of Michael Majerus' lecture
delivered to the British Humanist
Association on Darwin Day 2004.
The Peppered Moth: The Proof of
Darwinian Evolution. This is the
transcript of Majerus' lecture given at
the European Society for Evolutionary
Biology meeting on 23 August 2007. The
accompanying powerpoint presentation is
also available as a pdf file.
Majerus, Michael E. N.. "Industrial
Melanism in the Peppered Moth, Biston
betularia: An Excellent Teaching Example
of Darwinian Evolution in Action".
Evolution: Education and Outreach 2:
63–74. doi:10.1007/s12052-008-0107-y.
Accusations of data fudging and
scientific fraud in the case are found
to be vacuous. 
An interactive game to simulate how
evolution works with Biston betularia
