1 - Egg
- anatomy, oviposition
2 - Caterpillar
- hatching, feeding and development
- cannibals, carnivores and myrmecophiles
- survival mechanisms,
armature, camouflage / disguise
co-evolution with plants
- pupation, metamorphosis
- emergence, feeding
- mate location and courtship
10 - Adult
- daily routine, roosting, hibernation, lifespan
Evolution of the
first appeared on Earth in the late Silurian Period. The earliest
insects had a simple 2-stage lifecycle in which miniature versions of
the wingless adults emerged from eggs. Such insects are called
Apterygotes. Modern day examples include silverfish, springtails and
insects probably first appeared in the late Devonian or lower
carboniferous Period, when a 3-stage Exopterygote lifecycle evolved.
In this case wingless nymphs emerge from eggs. As the nymphs feed and
grow they periodically moult their skins. The stages between the
moults are called instars. During the later instars the nymphs develop
wing "buds", but it is not until the final moult that fully developed
wings are present. Examples of Exopterygotes include mayflies,
dragonflies, stick and leaf insects, katydids, mantises, earwigs,
cockroaches, lice, termites and shield bugs.
The most advanced insects, i.e. those
with a 4-stage lifecycle, evolved in the late Carboniferous Period.
These are known as Endopterygotes, examples of which include
lacewings, scorpion flies, caddis flies, true flies, fleas, bees,
wasps, ants, sawflies, beetles, butterflies and moths.
The lifecycle of butterflies was first
unravelled in 1600 by Maria Sibyella Merian, who observed that they
have 4 distinct phases of development : ovum, larva, pupa and imago (
adult ). Each stage of the lifecycle is sharply differentiated from
the last but is ontogenetically dependent on it. Individuals carry
genes which govern development at each stage of the lifecycle but
different genes come into play at each stage. Adult butterflies for
example carry caterpillar genes that are "switched off" and vice
versa. Mutant genes control features that are only present during part
of the lifecycle e.g. only adult butterflies have antennae, wings and
a proboscis. Behavioural features such as mate location, copulation
and migration are also controlled genetically by these mutant genes.
: anatomy, oviposition
The shape, size,
colour and texture of butterfly eggs varies greatly from one species
of Satyrines and Heliconiines are typically domed or barrel-shaped,
adorned with between 8-30 vertical ribs, between which can be seen
dozens of lateral ridges. Most Hesperiidae, Papilionidae and
Riodinidae produce smooth globular eggs. The eggs of Polyommatines
have a finely reticulated surface, and are shaped like flattened
do-nuts. Pierines produce tall skittle-shaped eggs, with fine
All butterfly eggs have
a depression at the top, in the centre of which is a hole called the
micropyle, through which sperm enters during fertilisation.
The egg shell also is peppered with
thousands of microscopic pores called aeropyles. Microscopic
examination of the eggs of Riodinidae, Lycaenidae and Limenitidinae
species reveals them to be adorned with hundreds of minute hexagonal
pits. Tiny hollow spines emerge at the intersections of each
hexagon. These are also aeropyles, and act as breathing tubes for
the developing larva.
egg details ©
In the case of Nymphalidae and most other butterflies the eggs are
already formed within the body of females when they emerge. They grow
in size over a period of 2 or 3 days as they mature within the
female's abdomen. Egg-laying is triggered when they reach a certain
size, at which time they pass from the ovariole to the egg chamber.
They are fertilised just prior to egg-laying, the male's sperm having
been stored until this time within a receptacle in the female abdomen.
Butterflies lay their eggs either singly or in batches, on or near the
foodplants that will be used by the caterpillars. Many species lay
their eggs away from the foodplant, on dry grass stems, dead leaves or
even on soil. This strategy prevents the eggs from being accidentally
devoured by grazing animals. It also makes it more difficult for
parasitoid wasps and flies to locate the eggs.
species, e.g. the Marbled White
galathea, drop their eggs randomly as they fly amongst
tall grasses, but most species have very precise requirements.
euphrosyne for example lays their eggs singly on
dead bracken or dry grass stems that are within a metre of their
caterpillar's foodplant, dog violet. The White-letter Hairstreak
w-album is even fussier, always laying it's eggs
on elm twigs, at the precise point where the new year's growth and old
paphia lay their eggs in chinks on the bark of oak
trees, but the larvae don't eat oak - they begin by eating their own
egg-shells, and then go into hibernation until the following spring,
when they descend the tree trunks to feed on the leaves of nearby
are often glued underneath the leaves of trees and bushes where they
are protected from rain and from the desiccating effects of hot
sunshine. In the Amazonian rainforests Heliconiine butterflies often
lay their eggs on Passiflora tendrils,
presumably to place them as far out of the reach of marauding ants as
normally feed on cuckoo flower or garlic mustard leaves, but if
they encounter another caterpillar they become cannibalistic. It would
therefore be wasteful if more than one egg was laid on each plant, so
the butterflies have evolved the ability to detect eggs that have
already been laid by other females. Studies have shown that many
members of the subfamilies Pierinae, Heliconiinae, Danainae and
Papilioninae have this ability, and avoid laying on plants carrying
eggs laid by other members of their own genus or species.
larvae of most species will only eat the leaves of one or two species
of plant and will die if they find themselves on the wrong type of
tree, bush or herb. Even oligophagous species - those that are able to
feed on more than one type of plant - have a hierarchal order of
foodplant preference, only accepting less nutritional species if they
are unable to locate their preferred foodplant.
therefore spend a great deal of time checking various leaves to
ascertain whether they are of the correct species for egg-laying.
Studies have shown that Heliconius,
and Perrhybris butterflies initially
determine leaf choice by shape and size, but use taste and smell to
confirm that the leaf is chemically "correct".
It is common to see butterflies flitting from plant to plant,
alighting momentarily on leaves, tasting the foliage using olfactory
sensors on their feet.
All female butterflies have spines on the underside of their
forelegs. When they land on a leaf these spines puncture the
surface, releasing aromas that are detected by the olfactory
just enough to locate the correct species of plant. The eggs usually
have to be laid on tender young leaves or buds, as the older leaves
often contain toxins that can kill them. They also have to be laid on
plants that are growing in very precise conditions - just the right
degree of shade, just the right conditions of temperature and
humidity, and at a height on the plants where they will not get eaten
by browsing herbivores. Eggs are often laid on the tips of buds,
usually quite high up on the tree or bush. This way they are less
likely to be found by ants. Female butterflies often spend long
periods probing about with the tips of their abdomens, being extremely
careful about the positioning of each individual egg.
In Peru Perrhybris
pyrrha females habitually alight on almost any available leaf
except ferns when searching for the Capparis
leaves on which they eventually oviposit. A female will reject several
Capparis trees before selecting a
particular one. Having found a tree that suits her she will then spend
up to 30 minutes comparing dozens of leaves. She will settle on a
leaf-tip, run up towards the base of the leaf as if measuring it, and
then move on to another leaf. Eventually she narrows her choice down
to just two adjacent leaves and then spends several minutes skipping
back and forth between them before finally deciding which leaf to
oviposit on. If she is disturbed part way through the oviposition
process she will flee up into the canopy, but will return a few
minutes later, relocate the leaf and complete laying the egg batch.
that induce a female to lay on a particular specimen of tree or bush,
or on a particular leaf, are often a mystery to human observers.
Gonepteryx rhamni always lays its eggs
I have counted up to 19 on a single leaf, and up to 100 on a tiny
bush. These may have been laid by a single returning female or by
several females in succession. These figures pale into insignificance
however when learning about observations of various
Capparis feeding species - In Kenya in
1926 Somersen estimated that a single 1 metre high bush of
Capparis held about 57,000 eggs and young
larvae of Belenois aurota. In Sydney,
Australia during a mass migration of Caper Whites
Anaphaeis java, Waterhouse estimated that
about 250,000 eggs were laid on a single 5 metre high Caper tree!
Laying in batches
Butterflies usually lay the bulk of their eggs within the first few
days of their lives. Older females lay smaller eggs, and the resulting
caterpillars take longer to mature, making them more prone to
predation and parasitism. This is probably part of the reason why
Perrhybris and numerous other species
avoid delay, and have evolved to lay all of their eggs in a single
batch immediately after copulation. This strategy also ensures that as
many eggs as possible are laid before the butterfly falls prey to a
bird, reptile, wasp or spider.
leaf, species unknown, Peru ©
Some species lay their egg batches in neat clusters like that shown
above, while others including Aporia,
Chlosyne and Aglais produce untidy
heaps in which the eggs are up to 3 layers deep. I have also seen
cases where Euphydryas aurinia females
have laid their eggs on top of an egg batch produced by another female
of the same species.
batches improves the survival prospects for individual caterpillars.
Wasps preferentially parasitize eggs at the edges of batches because
they cannot easily reach those at the centre with their ovipositors.
It seems that a few individual eggs around the edge of the batch are
sacrificed to ensure that the bulk of them at the centre of the batch
are left alone. Eggs at the centre are also
less likely to be eaten by predatory insects, and are
protected against desiccation.
As might be
expected there are also negative factors involved when a butterfly
"puts all it's eggs in one basket" - an entire egg batch could be
deliberately eaten by a bird, snail, reptile or amphibian; or
accidentally consumed by a grazing animal. To reduce the likelihood of
this happening butterflies choose their egg-laying sites with great
Nymphalidae genera including Hamadryas,
Araschnia lay their eggs in long vertical strands, dangling
from the underside of leaves. Hamadryas
amphinome sometimes lays in strands of up to 15 eggs long. It
is not known what advantage the butterflies gain by adopting this
strategy - perhaps the eggs at the end of the string are less
susceptible to leaf mould?
egg batch of Marsh Fritillary Euphydryas aurinia,
Wiltshire, England ©
egg batch of Small Tortoiseshell Aglais urticae,
Hampshire, England ©
With many species of butterfly the eggs need to mature within the
female for between 3-6 days before egg laying commences. Once this
period has elapsed, oviposition activity is controlled at least
partially by the butterfly's inbuilt biological or "circadian" clock.
Hence she will only lay her eggs at a particular time of day, during
which her activities adhere to a "rest-feed-fly-oviposit" sequence.
This is triggered and modified by environmental cues such as
temperature and light levels. The "oviposit" part of the sequence,
often referred to simply as an egg-laying run, typically lasts for
about 5 minutes, but can be shortened if cloud obscures the sun and
incubation period varies greatly from species to species. Eggs of
tropical butterflies usually hatch within a week, but in temperate
areas 10-14 days is more typical. There are however many species, such
as Purple Hairstreak
Lysandra coridon and High Brown
Argynnis adippe, in which the eggs hibernate over
winter, and in these cases the incubation period can last for several
The eggs of butterflies and moths are valuable
sources of protein. In addition to the threats from birds, snails,
reptiles, amphibians and grazing mammals already mentioned, they are
prone to parasitisation by microscopic wasps and flies.
seem surprising that something as small as a butterfly egg has its
own parasitoids, but these cause high losses. The main parasitoids
are wasps in the families Scelionidae and Trichogrammidae - as many
as 60 of these can emerge from a single butterfly egg !