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
: pupation, anatomy, metamorphosis
When a larva becomes
full grown, it undertakes a final moult to become a pupa. For a day
or two prior to pupation the larva goes through a wandering phase
when it usually leaves its foodplant and may walk up to a kilometre
before finding a suitable place to undertake the transformation into
a pupa. During this phase it is very prone to predation. Dispersal
however probably reduces overall predation of pupae by spreading
them over a wider area - if they were concentrated on or around the
foodplant it would be easier for birds to home in on them and wipe
out the whole brood.
Larvae pupate in different ways
depending on which family they belong to. A larva from the family
Nymphalidae for example will spin a tiny button of silk on a leaf or
stem, and anchor itself to it by its tail. The tail has an appendage
called a cremaster, which is equipped with microscopic hooks to hold
it securely to the silk. Larvae of Papilionidae and Pieridae do the
same, but additionally spin a silken girdle around their waist.
Lycaenidae and Riodinidae don't possess cremasters so they either
pupate on the ground, or attach themselves by a silk girdle to a
leaf or stem. Hesperiidae pupate loosely, usually within a flimsy
silken tent. The larvae of most moths pupate loosely in a chamber
just below the surface of the ground. Others, including Saturniidae,
Bombycidae and Lasiocampidae pupate inside a tough silk cocoon spun
on the leaves, stems or branches of their foodplants.
The pre-pupal caterpillar remains
motionless for 2-3 days preparing itself for its final moult. During
this time the prolegs start to shrink, the thoracic segments become
enlarged, and the larva adopts a curled hump-backed position.
fully grown larva ( pre-pupa ) just
prior to the final moult ©
the final moult takes place the skin splits behind the head, but
instead of a caterpillar walking out of the old skin, what emerges is
quite different in nature - a legless, wriggling, non-eating entity
called a pupa or chrysalis.
first the pupa is soft, limp and highly vulnerable to attack by
parasitoid wasps and flies. Within a few hours however the skin
hardens into a tough shell that will protect the insect until it
ultimately emerges as an adult butterfly or moth.
The pupae of many Lycaenidae species are attended by ants ( see
myrmecophily ). The presence of ants
is beneficial to the pupae because ants drive away predatory insects
and parasitoid wasps that would otherwise attack them. Experiments
with the Australian hairstreak Jalmenus evagoras
for example have shown that in cases where ants have been denied
access to the pupae the latter have suffered up to 95% parasitism by
the wasp Brachymeria reginia. Conversely,
pupae attended by the ants experienced zero parasitism.
( Nymphalinae ),
show no external evidence of sexuality, but pupae can be distinguished
as male or female. A male pupa will have 2 tiny bumps close to it's
tail, corresponding with the anal claspers of the adult butterfly or
moth. It is also usually slimmer and lighter than a female pupa. Many
other anatomical details of the adult butterfly can be seen on the
pupa - e.g. antennae, legs, eyes, wing cases and palpi.
( Pierinae ), pupa attached to garlic mustard stem ©
Butterflies in the families Nymphalidae, Papilionidae and Pieridae
usually pupate openly, attached to leaves, stems or twigs.
These unprotected pupae are highly vulnerable to predation and
parasitism. They are usually cryptically coloured and patterned to
resemble foliage, lichens, bird droppings or other common natural
protective resemblance makes it much harder for birds and small
mammals to locate them, and increases their chances of survival.
species of Papilionidae and Pieridae are able to increase their
chances of survival individually, by producing pupae which differ in
colour according to their surroundings. Laboratory experiments have
shown that on the days prior to pupation caterpillars can detect the
colour of the surrounding vegetation and that this triggers a
genetic response which decides whether the ultimate pupa will be
green or brown.
Pararge aegeria ( Satyrinae ), pupa
attached to pendulous sedge ©
butterfly pupae in addition are adorned with spines, keels, knobs
and other protrusions. They are also frequently contorted into
strange shapes. The overall effect is that they often very strongly
resemble twisted and desiccated dead leaves or bits of wood. Other
butterflies such as Ithomiinae and Danainae are smooth, bulbous and
silvery, looking like glistening rain drops.
pupa, probably melpomene ( Heliconiinae
), Rio Madre de Dios, Peru ©
use of protective resemblance as described above is a form of
passive defence, but there are a small number of pupae which use
neotropical Brassoline Dynastor darius
resembles a snake's head. Another
is the pupa
Head Hawkmoth Acherontia atropos, which
wiggles and squeaks if molested. The squeaking sound is produced by
forcing air in and out of the spiracles.
Skipper larvae ( Hesperiidae ), and those of moth families including
Lasiocampidae, Arctiidae, Saturniidae, Notodontidae and Zygaenidae
pupate within cocoons. These
range from flimsy affairs composed of little more than a few strands
of silk, to hardened shells made of dozens of layers of silk
interwoven with bits of chewed bark, such as that of the Puss moth
Some cocoons are formed among
living foliage on trees and bushes, while others
that of the American Moon moth Actias luna
are formed among dead leaves
on the forest floor. The cocoon of the Emperor moth
Saturnia pavonia has a lobster-pot design with a special
"door" which allows the moth to make its escape, but prevents other
creatures from entering.
One of the strangest and most
beautiful cocoons is that of the Amazonian moth
Urodus ( Urodidae ) which has a coarse
open mesh design with an exit at the bottom, and hangs like a
pendulum from a 20cm long silk cord. It seems likely that the cord
may function to isolate the pupa from marauding ants, but little is
known about the biology of this species.
The cocoons of the silkworm moth
Bombyx mori (
Bombycidae ) have been used for centuries for the production of
silk. Several species in the family Saturniidae including
Antheraea mylitta also produce silk of
The pupal stage of the lifecycle can last anything from 1 to 40
weeks depending on the species. In polyvoltine species ( those
which have more than one generation per year ), the summer pupal
stage will be short - often just a few days; but the 2nd brood
may overwinter as a pupa from August or September until the
following May or June.
Some species occasionally delay their emergence and remain as
pupae for 2 or more winters. This is a natural safeguard because
in an unusually short or harsh summer a species might be unable
to breed in viable numbers. By staggering its emergence over 2
or 3 years it spreads the risk and ensures that at least a few
adults will appear and reproduce each year, regardless of the
that the bodily fluids within the pupa break down into a "soup" and
later reform in the shape of a butterfly is largely untrue. The change
from larva to adult butterfly is actually a very gradual process.
Clusters of stem cells from which the wings develop are present in
segments 2 and 3 of small larvae. They replicate and diversify during
larval development. In the last few days prior to pupation the
development accelerates, so that the wings are almost fully formed at
the time of pupation. The same applies to the antennae, eyes and
palpi, all of which are visible on the newly formed pupa.
Within the pupa the changes that take
place are surprisingly minor. The wing scales develop as plate-like
extensions from cells on the wing surface. The heart, brain, eyes,
antennae, proboscis etc all develop from the fairly simple organs
"hidden" within the larva, into the recognisable features of an adult
with wing patterns showing through, just prior to emergence ©
2 or 3 days before the butterfly is due to emerge
it changes colour, and the colour and pattern of the wings can
usually be clearly seen.
At this stage female pupae of many species exude
pheromones which attract males even before the butterfly has
Costa Rica e.g. I have observed that female pupae of
Heliconius erato, when close to
emergence, often have several male adults in very close attendance.
A frantic battle takes place the instant the female hatches, as all
the males struggle to copulate with her, not even allowing her time
to expand and dry her wings. The mated pair then have to endure the
continuing aggravation of the remaining males, which are often
extremely persistent, trying to prise the pair apart. Eventually,
with the approach of dusk, the unsuccessful males disperse, allowing
the pair to remain copulated until the next morning.