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Frequently Asked
Questions :
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Why do butterflies
rest in a head-downwards position ?
Hamadryas februa male, Yarinacocha,
Ucayali, Peru
There are several
reasons for this. Many Nymphalids including Hamadryas, Prepona, Panacea
and the Red Admiral Vanessa atalanta habitually bask high up on tree trunks, with wings outspread,
and head downwards. They often appear to be observing the
activity below them, and males certainly use these high vantage
points to watch out for females flying below them in the forest.
An additional advantage of adopting this position is that
sunlight hits the wings more squarely, allowing the butterflies
to warm themselves more quickly.
Another reason is linked to
aerodynamics. Studies have demonstrated that butterflies get greater
"lift" if they take off from a head-downwards position. The
hibernating Comma pictured below has chosen a small branch just
a few inches above the ground as it's over-wintering site. The
butterflies probably make use of the heat reflected up from the
leaf litter, and in conjunction with the more efficient
head-downwards take-off, can become airborne more easily on the
cold but sunny days of late winter and early spring.
Comma
Polygonia c-album, hibernating openly under a low branch.
Tropical Riodinids such as Eurybia
habitually rest beneath low growing foliage, and probably make
use of the same factors to enable them to take flight very
rapidly, to intercept potential mates.
Eurybia species, probably
molochina, Madre de Dios, Peru
Where do
butterflies go when it rains ?
Most species shelter under leaves when
it rains. They can
often detect the approach of wet or windy weather
several hours before it's arrival ( by sensing changes in
humidity and air pressure ), and take
shelter well in advance of rainfall.
I've observed this many times
especially in the neotropics when
Cattlehearts,
Sisters and many other species
suddenly disappear under leaves even when the sun is shining.
You can be sure however that when they do so things are on the
change. Clouds quickly roll in, and an hour later it's pelting
down.
There is a short account of my observation of similar behaviour
by Gonepteryx
rhamni in England, on the
Brimstone page.
Gonepteryx rhamni, and many other species, roost under
leaves at night or in wet weather.
Not all butterflies shelter under leaves though - some such as
Peacocks hide in rabbit burrows, while Commas go into log piles
or hollow tree trunks, and
Orange tips just sit it out on the surface of a leaf or on a
flower head. Blues, browns and most
skippers rest openly on grasses in dry
weather, but the threat of rain sends them deep into grass tussocks for shelter.
Dingy Skippers stay out in the open even
during prolonged spells of bad weather - in May 2006, I studied
one particular female Dingy Skipper which spent no less than 13
days sitting on
the top of a knapweed plant, with it's wings wrapped
tightly around a dead flower
head. It endured heavy rain, hail,
sleet and strong winds during this period, with no opportunity
to feed. The butterfly is superbly camouflaged when resting on knapweed
seed-heads, where it is overlooked by insectivorous birds. By roosting high on the
seed-head, it is also able to escape
predation by rodents, which might more easily locate an insect
that chose to hide amongst grasses at ground level.
Dingy Skipper, female at
roost, Selborne, Hampshire. During prolonged
periods of wet weather, the butterflies remain out in the open for
a week or more, with their wings wrapped tightly around the dead flower
heads of knapweed plants.
Why do butterflies
migrate ?
When butterflies first appeared on
Earth, the present day continents were all connected to form one
giant land mass. Nature tries to fill every available niche, so
butterflies would have naturally been nomadic, their colonies
moving seasonally from one area to another in search of suitable
habitats.
As the continents drifted apart,
species with weak flight became increasingly unable to cross newly forming natural barriers
such as oceans and mountain ranges. Certain species however were more robust,
and managed to overcome the barriers. In some species the
inclination to migrate became imprinted genetically, and they
still migrate today - if/when environmental conditions are
suitable.
The
most famous migratory butterfly is the Monarch
Danaus plexippus,
which migrates annually over a distance of 2000 miles ( 3200km )
between it's northern breeding territories in Canada, and it's
southern over-wintering grounds in Mexico. Read more about the
Monarch
here.
Monarchs
Danaus plexippus migrate each year from Canada to Mexico, where millions hibernate, completely covering the
trunks and foliage of fir trees in the mountains.
( image
© Ingo Arndt )
The story of the Monarch - click here.
Why do Hairstreaks
rub their wings together ?
Hairstreaks usually have a pattern
of lines or stripes on the underside wings. These, in
combination with ocelli ( false eye markings ) and short tails (
false antennae ) act to divert attention away from the head, and
towards the outer edge of the hindwings. By oscillating the
wings, the tails are made to wiggle like antennae, further
increasing the illusion that the butterfly is "back to front".
Attacking birds will always aim at the head of a butterfly, but
are tricked into aiming at the tail. The butterfly is thus able
to escape in the opposite direction unharmed.
Another
reason for wing-rubbing is that male Hairstreaks have patches of
specialised wing scales - "androconia", located on their
upperside forewings. Sacs at the base of these scales contain
pheromones. Rubbing the wings together probably helps to
disseminate the pheromones, which attract females and induce them
to mate.
Spindasis
seliga, Gopeng, West Malaysia
Why do Whites bask
with their wings half-open ?
This activity is called
reflectance basking. Butterflies with dark wings usually
open them fully when basking, to expose the maximum area to the
sun's rays, enabling them to warm up rapidly and gain energy.
Whites, Blues and Coppers however have wing surfaces which
reflect, rather than absorb solar energy. Consequently they bask
with their wings half open, so that the heat produced by
sunlight falling on the dark thorax is contained within the
"cage" of the half-open wings, rather than being dispersed on
the breeze.
Small White
Pieris rapae, 2nd brood female,
Noar Hill, Hampshire, England
How much
rainforest is destroyed every year ?
A very difficult question to
answer, because some areas are entirely destroyed, while other
areas are left semi-intact, but severely degraded.
In excess of
10,000 square miles ( 2.6 million hectares ) of the Amazon
rainforest is deliberately burnt down every year, primarily to make way for cattle pastures. These
pastures are very poor in nutrients, so support only very small
numbers of cattle. The pastures are burned annually to promote
new grass growth and to destroy cattle parasites. These fires
rage uncontrolled, setting fire to further areas of forest.
Deforested areas are much hotter and drier than the rainforests
- consequently the average temperature of the entire region
rises and the humidity falls even more dramatically. This causes
major changes in the vegetation structure of the remaining areas
of rainforest, leading to reduced biodiversity even in protected
areas.
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The Amazon
rainforests of Brazil - burnt down to make way for soybean
plantations and temporary cattle pastures. |
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A soybean
plantation in Brazil - 10 years ago this was a pristine
rainforest, habitat of over a thousand species of butterfly, 500
birds, and countless other wild creatures. |
In Borneo enormous areas of forest have
been logged or burned, killing thousands of orang-utans. Almost
all of the tropical rainforest in Western and Central Africa has
already gone, and the same applies to India, Madagascar, and
Malaysia.
Please visit the
Rainforests page to see how YOU can help to protect the
areas that remain.
What are the red
bits on this Marbled
White ?
Marbled White Melanargia galathea,
with
Trombidium breei mites on thorax.
Adult butterflies, particularly
the males of Meadow Brown Maniola
jurtina,
Marbled White Melanargia galathea,
and Common Blue Polyommatus icarus
are commonly parasitised by these red mites
Trombidium breei,
which normally attach themselves to the thorax of the butterfly.
They transfer from host to host when the butterflies alight to
nectar at flowers. Studies on Meadow Browns have shown that the mites have no
detectable effect on the flight performance, orientation ability
or lifespan.
Why
do Danaines feed
at dry, dead plant stems ?
The habit
which butterflies have of feeding at dry, dead plant stalks is not
confined to Danaines – it is also very common amongst Ithomiines,
and not unknown amongst Satyrines and
Nymphalines. I’ve even seen White Admirals doing it in
Britain.
Only male
butterflies indulge in this habit. The purpose is to acquire
pyrrolizidine alkaloids, which in the case of Danaines and
Ithomiines are chemically converted into pheromones.
These are later
disseminated via “hair pencil” scales on the abdomen
( Danaines ) or wings ( Ithomiines ), to entice females into copulation.
The
alkaloids are also known to be toxic to birds, inducing vomiting,
so that a bird which has tasted an Ithomiine or Danaine is
unlikely to attack another similarly patterned butterfly. It is
also likely that the alkaloids are passed to females during
copulation, and may be vital in the production of viable eggs.
How are butterfly populations
monitored ?
A
"transect" is one of several methods used to
monitor butterfly populations. Other methods include "mark and
recapture" and "species-related estimation".
Transects
This method involves an individual or group of
individuals who undertake a regular weekly walk that
follows a fixed route through a butterfly habitat. The route is
divided into sections, each
representing a different sub-habitat. A
transect at a woodland site for example might include a section
through a recently coppiced area, another section through a fir
plantation, and another through a stand of mature oaks.
The
butterflies seen in each section are counted, and the figures
compared to those obtained in other sections, or from the same
section in past years. The figures do not
represent accurate population counts, but are of value in
assessing how numbers fluctuate in response to management factors
such as grazing or coppicing regimes.
Unfortunately the method has many
disadvantages - a) conspicuous species such as Small Whites or
Brimstones can be easily counted, but smaller and duller species
such as Dingy Skippers and female Chalkhill Blues tend to be
greatly under-estimated; b) butterflies flying in open grassland
are more easily counted than those in woodlands; and c) the numbers of each
species which are active and observable vary greatly according to
climate, local weather conditions, time of day and other factors.
Mark and
recapture
This method involves capturing
every individual of a particular species, numbering and tagging it
by marking it with a spot of paint, and releasing it. The
following day the process is repeated, and the number of "missing"
butterflies is counted, while "new arrivals" are themselves
marked. Over a period of 2 or 3 weeks it is possible to analyse
the build up of populations, the lifespan of individuals, and the
movement of individuals from one part of the site to another.
The disadvantages are - a) it is
not possible to know why individuals go "missing" - do they die,
do they disperse or migrate, are they simply copulating or resting
and thus not captured ? b) this method works quite well for
certain species at small sites, but is impracticable at large
sites, and impossible for species such as Purple Hairstreak which
spend all day at the top of oak trees.
Species-related
estimation
This method uses a combination of
"field knowledge" and calculation. An experienced entomologist
might e.g. walk around a grassland site counting the numbers of
male Chalkhill Blues. Perhaps he / she counts a total of 300 males
in an hour.
This is doubled to 600 to take
account of the female percentage of the population. Next it is
multiplied by a factor which takes into account the area of the
site where similar habitat occurs - perhaps the walk only took the
entomologist through 10 percent of the habitat, so the figure
would be multiplied by 10 to give a total of 6000.
The count only took place for one
hour, on one day, but the species may have a flight season lasting
several weeks, so other factors must be taken into account :
What percentage of the total population had yet emerged ? What
percentage were flying during the hour that the count took place ?
Various formulae ( arrived at from mark and recapture data ) can
be applied to calculate the approximate total population size.
Multiplying the counted number of
individuals ( 300 ) by the appropriate factor might result in a
total population size as small as 1000, or as large as 20,000,
depending on the size of the site, the available habitat, the
behaviour of the butterfly, and at what stage in the flight season
the count occurred.
The disadvantages of this method
are - a) it is highly subjective - for it to have any comparative
value, the same entomologist and the same formulae would have to
be used at every site; b) areas of a site that appear to be
identical may hold vastly different numbers of butterflies - e.g.
some areas might have a deeper soil - a factor that affects the
vegetation mixture, sward height and microclimate.
What to do with a hibernating
butterfly in my house ?
The best
course of action is to put the butterfly outside, making
sure it is cool and protected from wind and rain, but in a
position where the sun will reach it when it is time to
awaken in spring.
You could
place it within a pile of logs for example, in a hollow tree
trunk. The most important thing is that it
must have an escape route, and must be protected from birds,
and from spiders ( so don't put it in a shed or greenhouse
).
If the
butterfly wakes up and flies away on a sunny day in the
winter it will find its own way to another safe hiding
place.
What is the biggest insect that ever lived ?
Fossils of a prehistoric
dragonfly Meganeura monyi from
the order Protodonata make it the largest insect ever to be
found, with a full wingspan of 30 inches and a body length
of 18 inches. The Meganeura
dragonfly lived about 250 million years ago until it became
extinct at the end of the Paleozoic Era. It flew in Britain
and France at a time when the climate in Europe was
tropical.
What is the fastest flying butterfly ?
The Monarch
Danaus plexippus is thought to be the
fastest flying butterfly, with a top speed of up to 20 mph in
still air. However several hawkmoths (
Sphingidae ) have been measured at speeds of over 30mph. The
fastest flying moth however is the Black Cutworm ( Noctuidae )
Agrotis ipsilon which can reach
flight speeds of up to 70mph / 113kph.
more questions.... >>
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