- the relationship between organisms and their environment
habitat management |
predators & parasitoids |
This page provides a brief introduction to butterfly ecology. For
full details about the ecology of individual species, please
refer to the relevant species pages, accessed via the
Species Index or from the
A few species of
butterfly are generalists, able to exist in a wide variety of
habitats. The adults can feed on nectar from a wide range of
flowers, and the caterpillars are able to feed on the leaves of
several different types of plant. Most butterflies however are far
more specialised, each species having it's own particular
requirements regarding habitats, temperature, humidity, larval
foodplants and adult food sources.
Often the relationship between a
butterfly and its larval foodplants only benefits the butterfly,
and many plants actively defend themselves against being eaten.
Passiflora plants for example produce
tiny growths which resemble butterfly eggs, deterring
Heliconius butterflies from laying
real eggs on them. They will not lay further eggs if others are
already present, presumably because the larvae are cannibalistic.
Many plants defend themselves by producing toxins that can kill
larvae, but the larvae are often able to evolve methods of
combating this defence. Some species for example have learnt to
bite though the stem or main leaf vein, to prevent the toxins from
reaching the leaf tissue.
Other species have become immune to
the toxins, but store them within their bodies so that they become
poisonous themselves. These species usually "advertise" their
acquired unpalatability to birds, by evolving bright warning
colours. Consequently most birds leave these butterflies alone,
but some have found ways of dealing with them. Great tits e.g.
have learnt that they can decapitate larvae and extract their guts
to dispose of the toxic contents, before consuming the edible
the rainforests of Amazonia many butterfly species are involved in "mimicry
complexes" whereby several different
species with varying degrees of toxicity share almost
identical wing patterns that warn birds about their actual or
supposed poisonous nature. The toxic models include orange and
black "Tiger" butterflies in the tribes Danaini and Ithomiini, and
near-identical mimics from the Heliconiinae, Nymphalinae and
Although relatively little
is known about the lifecycles and ecology of the majority of
butterflies and moths, it seems likely that a large number of species are
involved in mutually beneficial relation-ships with other
In some cases the relationship is obvious and simple - e.g.
butterflies pollinating flowers in exchange for nectar, but in
many species it is very complex and can involve several species of
organism at different stages of the butterfly's lifecycle.
relationship between two or more organisms
Maculinea arion, have a symbiotic
relationship with Myrmica sabuleti
The caterpillars of many
members of the family Lycaenidae have evolved to become carnivorous,
feeding on ant grubs, aphids or coccids. One of the best studied
examples is larva of the
Large Blue which feeds when very
small on the flowers of thyme Thymus pulegioides,
but after a few weeks, when it has reached it's fourth
instar, it secretes pheromones which induce a species
of red ant Myrmica sabuleti, to
carry it underground into the ant's nest. For the rest of it's
life, the larva eats ant grubs !
The larva is tolerated by
the ants because they are able to "milk" it, obtaining
a sugary substance which is exuded from its dorsal "honey
gland". The larva hibernates, and later pupates in the ant's nest.
butterfly emerges from the pupa, it uses another pheromone to
appease the ants, enabling it to crawl unharmed along the ant tunnels to reach the
where it can dry it's
wings and fly away.
The Large Blue is totally dependent on the ant Myrmica sabuleti for it's
survival. The ants also have their own specialised
requirements regarding habitat, which greatly limits the areas in
which the butterfly can breed. If the ant colonies die out, the
Large Blue colonies die out.
Generalists and specialists
The Large Blue is
an example of a highly evolved specialist. Most
are less specialised, but still have quite precise
requirements regarding habitats, larval foodplants, adult food
sources and climate.
A typical example is the
Hairstreak, a butterfly of temperate deciduous woodlands,
which exists in very localised colonies, often based on a single elm
The butterfly lays it's eggs on elm twigs, and the caterpillars
hatch a few days after the flowers appear on the tree in early
spring. When tiny they feed within the flowers, but when the flowers
have withered and died they feed openly on the elm leaves. The adult
butterflies emerge in mid-summer and spend most of their lives at
the top of the trees, but occasionally descend to feed on the nectar
of thistles and other flowers.
In a "normal" summer the females lay all of their eggs on the same
individual tree upon which they fed as larvae.
The same happens with most other butterfly species - in normal
seasons they are surprisingly sedentary in behaviour, so much so
that many species never fly more than a hundred metres or so away
from their emergence site.
exceptionally warm summers, females still tend to lay most of their
eggs on their home territory, but later disperse,
migrating across the
countryside in search of other suitable sites where they can lay
their remaining eggs.
White-letter Hairstreak, a scarce species
dependent on elms
Let's look at
another example, the
Fritillary. Sites for this
species need to have an abundance of dog violets ( the caterpillar's
foodplant ), and bugle ( the main nectar source used by the
adults ). The sites also need to meet fairly strict criteria
regarding temperature and humidity.
Furthermore, because the
caterpillars hibernate during the winter, the areas where they feed
must be exposed to sunlight at the critical stage when they reawaken
in early spring. The number of sites which fulfil all these criteria
is very limited, so the butterfly is generally restricted to sunny
clearings in woodland, where violets and bugle grow in profusion.
Clossiana euphrosyne, depend on
transitional woodland habitats
Woodland clearings are of course an
unstable habitat - bare ground is quickly colonised by coarse
grasses, then by bramble and bracken, or is replanted with new
trees. Either way, the clearing quickly becomes overgrown, and the
violets and bugle get shaded out. When this happens, the clearing is
no longer capable of supporting the butterflies. If they are unable
to colonise another clearing in the immediate vicinity, the
butterflies die out.
management is affected by a multitude
of factors including government policies, demand for timber / pulp /
charcoal, timber extraction methods etc. When woodland
management changes on a national scale, and becomes incompatible
with the requirements of a particular species of butterfly, the
result is that the species follows a trend of decline, and
ultimately becomes extinct.
Each species has it's own "catastrophe
threshold" - once the amount of suitable breeding habitat falls
below a certain level local extinctions occur and the species
contracts towards areas where more extensive areas of suitable
habitat remain. Even then the species often continues to decline
because the gene pool is reduced. Reduction, fragmentation and
isolation of habitats means there is little or no opportunity for
fresh genetic material to arrive, and ultimately the species is
If butterflies and other
to survive, it is vital that conservation and land management are
coordinated at national
level to ensure that sufficient areas of habitat are maintained in
suitable condition throughout the country. It is also essential to
ensure that existing areas of habitat are linked together by
creating and maintaining a network of natural corridors (
woodlands e.g. can be linked by hedgerows and small copses, while
grasslands can be linked by roadside verges ) so that butterflies
and other wildlife can easily migrate between sites.
information about the conservation and management of Britain's
woodlands, grasslands, heaths and coastline see the
Habitats in Britain page.
earlier at Large Blue / Myrmica sabuleti
symbiosis. Symbiosis is defined as a mutually beneficial
relationship between organisms. There are also many non-beneficial relationships, such
as parasitism and predation, where one species benefits at the
expense of another.
All stages of
the lifecycle are threatened by parasitoids - creatures which feed
on other organisms and eventually kill them. There are for example
minute wasps which inject their eggs into the eggs of butterflies,
feed on the developing larva within, and emerge as adult wasps from
holes in the butterfly eggs. Other wasps such as
and flies ( Tachina etc ) spend their
larval stage feeding within the bodies of caterpillars, which die shortly after the parasitoids vacate them.
Other tiny wasps, including the brilliant metallic green Pteromalus
puparum, attack newly formed butterfly pupae.
particularly males of Meadow Brown Maniola
jurtina, Marbled White
Melanargia galathea and Common Blue
Polyommatus icarus often have tiny red mites
attached to them, usually on the thorax. Studies have shown that the
mites have no detectable effect on the flight performance,
orientation ability or lifespan of infested Meadow Browns, so this
could be regarded as a non-harmful form of parasitism.
butterflies however are killed in huge numbers by insectivorous birds,
dragonflies & spiders. Orb spiders catch butterflies in their webs,
and crab spiders lie in wait on flowers, ambushing them when they visit
in search of nectar. Vast numbers of caterpillars are eaten by birds, and lesser numbers by heteropteran bugs, solitary
wasps, mantises, lizards, toads, mice and other predators.
information about predators and parasitoids see the
Enemies of Butterflies pages.
parasitism and viral / fungal infestations cause very heavy population losses. A butterfly may be capable of laying 500 or so
eggs, but in practice only about 50 are laid on average, as most
females die before they are able to lay all their eggs.
percent of those eggs will hatch, but at least 90 percent of the
caterpillars will be eaten by birds, or killed by parasitoids, and
fail to reach pupation. At least half of all wild pupae will be
consumed, be killed by parasitoids, or die from fungal attack. When
the butterflies emerge from the surviving pupae, many more will be killed
before they have time to mate and lay their eggs.
Marsh Fritillary Euphydryas
The effects of climate
Theoretically, if populations
are to remain stable from year to year, only a single fertilised
female needs to survive from that original figure of 500 eggs.
Butterfly populations are
rarely stable though - poor weather during the flight
season greatly reduces mate-locating and egg-laying opportunities,
mild winters increase the likelihood of over-wintering larvae and
pupae succumbing to fungal attack or viral diseases, and a succession of warm springs can have a very detrimental
affect on species such as the
which over-winter as larvae :
If the weather
in early spring is cold and sunny the larvae warm themselves up by
basking on dead leaves, and are able to feed and develop quickly.
Their parasitoid however, the wasp
Apanteles bignellii over-winters as a pupa, hidden in the
shade amongst grasses, and develops slowly. Consequently when the
adult wasps emerge they discover that most of the caterpillars have
already pupated. A few weeks later large numbers of Marsh
Fritillaries emerge and breed. In warm springs however the wasps
are able to emerge early and find large numbers of caterpillars to
attack, resulting in a low emergence of Marsh Fritillary adults.
It can be seen
from the above that a couple of
successive warm springs, combined with dull or wet weather during
the butterfly's flight season can easily be enough to cause the
extermination of a small colony of butterflies.
In the past,
when human populations were much lower and more wild habitats existed, butterfly populations could naturally re-establish themselves, as
there were always other colonies nearby. Sadly, in the modern world,
wild habitats have been fragmented, and butterflies are usually
unable to find their way across the vast expanse of sterile farmland
and urban sprawl to recolonise sites.
Once a species
is lost from a site, it is probably lost for ever, unless man intervenes. New
habitats need to be created, and existing sites need to be managed
for butterflies, and linked by a network of
natural corridors. Consideration also has to be given to artificial
population maintenance via reintroduction and genetic diversity