THE LIFE CYCLE OF BUTTERFLIES AND MOTHS (LEPIDOPTERA)
© REG FRY 2014
The life cycle or life history of Butterflies and Moths is:- The Egg or Ovum, The Caterpillar or Larva, The Chrysalis or Pupa and finally the Adult Butterfly or Moth (the Imago).
BUTTERFLY AND MOTH EGGS
Eggs come in an incredible variety of shapes, sizes and markings. Those that are going to hatch out within a week or two are often laid on a leaf, some on the upper side of the leaf and some on the underside and they may be laid singly, in pairs or in a large batch depending on the species. A few species drop their eggs into grasses when in flight. Many species that overwinter as eggs lay them on the trunk, branch or twig of a tree and often close to a bud.
Examples of the eggs of twelve butterfly species are shown below. Starting from the top left the species of the eggs is as follows:-
Row 1: The Comma (Polygonia c-album), Dark Green Fritillary (Argynnis aglaja), Purple Hairstreak (Neozephyrus quercus)
Row 2: White-letter Hairstreak (Satyrium w-album), Adonis Blue (Lysandra bellargus), Wall (Lasiommata megera)
Row 3: Scotch Argus (Erebia aethiops), Silver-spotted Skipper (Hesperia comma), Dingy Skipper (Erynnis tages)
Row 4: Small Copper (Lycaena phlaeas), Green-veined White (Pieris napi), Orange-tip (Anthocharis cardamines)
NOTE: The life history available so far for each species can be seen by clicking on the scientific name in the above list.
Examples of the eggs of eighteen moth species are shown below. Several of these are quite fragile such as the top left egg which is soft and rather like a small blob of jelly. Starting from the top left the species of the eggs is as follows:-
Row 1: The Festoon (Apoda limacodes), Grass Eggar (Lasiocampa trifolii), The Lappet ((Gastropacha quercifolia))
Row 2: Poplar Lutestring (Tethea or), Small Emerald (Hemistola chrysoprasaria), Maiden's Blush (Cyclophora punctaria)
Row 3: Barred Straw (Eulithis pyraliata), August Thorn (Ennomos quercinaria), Canary-shouldered Thorn (Ennomos alniaria)
Row 4: Swallow-tailed Moth Ourapteryx sambucaria, Feathered Thorn Colotois pennaria, Pine Hawk-moth (Hyloicus pinastri)
Row 5: Clouded Buff (Diacrisia sannio), Rannoch Sprawler (Asteroscopus nubeculosa), Green-brindled Crescent (Allophyes oxyacanthae)
Row 6: Alder Moth (Acronicta alni), Copper Underwing (Amphipyra pyramidea), Light Crimson Underwing (Catocala promissa)
THE CATERPILLAR OR LARVA
Most caterpillars have 3 pairs of true legs and with a few exceptions up to 5 pairs of prolegs or claspers as illustrated in the picture below. The true legs are segmented with joints and become the walking legs in the adult butterfly or moth. In most cases the number of prolegs varies from 2 to 5 but some leaf-mining caterpillars and Limacodidae species have none and some Zygaenoidea have more than 5 pairs. The number of prolegs and their size is often helpful in determining which family or families the caterpillar is likely to be part of and hence can help in identifying which species it is, examples from a few families can be found below. As a caterpillar grows in size it becomes too large for its skin which it sheds, typically 4 times, before it changes into a chrysalis. In some cases the number of prolegs which are visible increases as the caterpillar grows and changes its skin.
WHAT'S THAT CATERPILLAR?
Trying to work out the species of many caterpillars is often very difficult, not only because of the large number of species but also because many caterpillars undergo a significant change in their appearance as they grow. One method that can be used to start the identification process is to try and work out which family grouping the caterpillar belongs to. The following gives some pointers to help decide which of the main family groups a caterpillar belongs to. The order in which the families are listed below is not taxonomic but is my own suggestion for working through some of the key identifying characteristics. This starts with caterpillars that only have two pairs of functional prolegs, then three pairs followed by the groups which, apart from a small number of exceptions, have five pairs of prolegs.
In the following examples I have also included pictures of the caterpillars that enthusiasts in the UK are most often asked to identify.
NOTE: If you want to see the life history that has been recorded so far for any of the species listed below, click on the scientific name and it will appear on a separate frame.
This is a large family with around 300 species either resident or regular migrants to the UK. Virtually all these species have only two pairs of prolegs, being without those on abdominal segments A3, A4 and A5. The absence of these three pairs of prolegs results in them moving by a looping process of arching and straightening the body - hence they are often called 'loopers'. The photograph of a Pale Brindled Beauty (Apocheima pilosaria) caterpillar is shown below. I am aware of a few species which are classified as Geometers which 'break the rule'. The Orange Underwing (Archiearis parthenias) (picture below) and Light Orange Underwing (Archiearis notha) both have varying size vestigial prolegs on segments A3 to A5. The March Moth (Alsophila aescularia) (picture below) and the Light Emerald (Campaea margaritata) both have vestigial prolegs on A5. The Scalloped Hazel (Odontopera bidentata) pictured below has two tiny pairs of prolegs on A4 and A5.
This is a small family with only 4 species resident in the UK and another an occasional migrant. The caterpillars of these 5 species are all missing a pair of prolegs on abdominal segment A3 and thus only have 4 pairs of prolegs. The picture below shows an example of the Least Black Arches (Nola confusalis).
There are six species in this family which are found in the UK. All have their anal claspers modified into a raised point and are therefore relatively easy to identify. Two examples are shown below, the Oak Hook-tip (Watsonalla binaria) and the Chinese Character (Cilix glaucata).
In this family there are 22 species resident in the UK and a few other occasional migrants. A few species are fairly hairy such as the Buff and Chocolate-tips. The Buff-tip (Phalera bucephala) larvae are gregarious until their final instar and their presence is often noticed because they strip braches of all their leaves. The Chocolate-tip (Clostera curtula) larvae are seen less frequently. Four species, the Puss Moth (Cerura vinula) and three Kitten moths have their anal claspers modified by a pair of tails. Some of the others such as the Lobster Moth (Stauropus fagi) also have their anal claspers modified and / or have strange shapes or colours such as the Pebble Prominent (Notodonta ziczac) and Lesser Swallow Prominent (Pheosia gnoma).
In the UK this is a small group with only 9 resident species, another two that regularly migrate to the UK and a further 6 species which, in most years, are much rarer migrants. In the UK members of this family are known as Hawkmoths and their caterpillars grow to the largest sizes seen here. All have five pairs of prolegs but their most distinctive feature is a tail horn. Two examples which illustrate the main tail horn shapes are shown below - the Privet Hawkmoth (Sphinx ligustri) and the rare migrant, the Death's-head Hawkmoth (Acherontia atropos). Below these are two images of the Lime Hawkmoth (Mimas tiliae), the example on the left shows the caterpillar in its final instar and on the right the colour it changes to when ready to change into a chrysalis (pupate). At this stage the caterpillar descends from the tree and is probably the most frequently seen Hawkmoth species because the caterpillars are often spotted crawling over the ground looking for a suitable spot to pupate in.
Another large caterpillar which is often seen feeding on the leaves of Fuchsia in gardens during the summer is the Elephant Hawkmoth (Deilephila elpenor). The way the caterpillar is sitting in the example below illustrates the reason that it was given its English name!
This is a large and varied family with around 350 species either resident or regular migrants to the UK. Most Noctuid caterpillars have 5 pairs of prolegs but 3 families have some species with one or two pairs missing or under-developed. In the subfamily Plusiinae, 14 out of 16 species have only 3 pairs - they are missing those on abdominal segments A3 and A4 as in shown by the example of a Golden Twin-spot caterpillar (Chrysodeixis chalcites) below. In the subfamily Hypeninae out of 11 species the proleg is rudimentary or absent on segments A3 and A4 in 4 species and is only rudimentary on segment A3 in 3 species - one example of the latter, The Snout (Hypena proboscidalis) is shown below although the partial proleg on A3 is not visible in this photograph. In the subfamily Catocalinae out of 7 species 1 only has a rudimentary proleg on A3, the Clifden Nonpareil (Catocala fraxini) and 3 species have prolegs rudimentary or absent on A3 and A4, one example being the larvae of Mother Shipton (Callistege mi).
One caterpillar that is often seen in gardens feeding on buddleia is the Mullein (Shargacucullia verbasci), shown above. It has five pairs of prolegs.
The larvae of the vast majority of Noctuid species are hairless or have very few hairs. However, there are 9 Acronicta species resident in the UK which are fairly or very hairy. These include three caterpillars that are often seen, the spectacular Sycamore (Acronicta aceris), the Grey Dagger (Acronicta psi) and the Knot Grass (Acronicta runicis) which are illustrated below. Another three interesting species in this family are the Dark Dagger (Acronicta tridens), Poplar Grey (Acronicta megacephala) and The Miller (Acronicta leporina). The other relatively hairy Noctuid species include the Scarce Merveille du Jour (Moma alpium), the Reed Dagger (Simyra albovenosa), Marbled Beauty (Cryphia domestica), Marbled Green (Cryphia muralis) and the Nut-tree Tussock (Cryphia muralis).
There are 8 members of this family resident in the UK. All are hairy and have five pairs of prolegs. Four species have a series of tufts on their backs and also have 'tails' which unlike the Hawkmoths are made up by a fairly thick bunch of hairs. The two most commonly seen examples are the Pale Tussock (Calliteara pudibunda) and the Vapourer (Orgyia antiqua) caterpillar which has tufts of hairs from either side of it's head as well as a tail. Two other species in this group are notorious for having extremely irritating hairs, the Yellow-tail (Euproctis similis) and the Brown-tail (Euproctis chrysorrhoea). These four species are some of the most commonly seen caterpillars and are pictured below.
There are 10 species of this family found in the UK, all are hairy and have five pairs of prolegs. Three of those most commonly seen here are the Lackey (Malacosoma neustria), the Oak Eggar (Lasiocampa quercus) and the Drinker (Euthrix potatoria). The Lackey used to be a relatively common caterpillar often seen in a group sunning themselves on fruit trees in gardens during May and June but are more often seen on hawthorn and blackthorn these days. The Oak Eggar caterpillars are one of the largest in this family at 65 to 80mm. The Drinker caterpillars are often seen on sitting on broad grass or reed stems in the autumn and spring and examples of this caterpillar before hibernation (left) and when fully grown are shown below. Another large hairy brown and black caterpillar which may be seen basking in the sun on open grassland in autumn and early spring, is the Fox Moth (Macrothylacia rubi).
Over 30 species of this family are found in the UK, all have five pairs of prolegs. Four examples are shown below. Those of the sub-family Lithosiinae are mainly feeders of algae and lichens and are all fairly or very hairy such as the Common Footman (Eilema lurideola) and the Four-dotted Footman (Cybosia mesomella). The other sub-family is the Arctiinae and almost all these caterpillars have thick hairy 'coats' including the well known 'woolly bear' the Garden Tiger (Arctia caja) and the Buff Ermine (Spilosoma luteum). The Buff Ermine caterpillar and a similar caterpillar the White Ermine (Spilosoma lubricipeda) are often seen walking along or across roads in September when ready to change into a chrysalis. The Buff Ermine is usually lighter in colour than the White Ermine and has a stripe on its side which is missing on the White Ermine. Another hairy member of this family which overwinters as a fully grown caterpillar is the Ruby Tiger (Phragmatobia fuliginosa) which is often seen in the late autumn and early spring. It is smaller than the two Ermines and its colour may be black as well as the brown example shown, in addition it may have a line running down its back - see the full set of pictures for examples.
There is only one member of this family of silkmoths resident in the UK. It is the Emperor Moth (Saturnia pavonia) which has 5 pairs of prolegs. The caterpillars feed on on a range of foodplants and are sometimes spotted on heather in heathland, they are gregarious in their early stages. The examples below show a 2cm caterpillar (left) and a final instar 6cm caterpillar, with some caterpillars the yellow colouring of the tubercules is replaced by pink.
There are 9 species of this family found in the UK, all have five pairs of prolegs and have few hairs. They are a bit of a mixed bag, the only significant feature they have in common is that most hide or feed inside spun-up leaves. Two examples are the curiously shaped Peach Blossom (Thyatira batis) and the Yellow Horned (Achlya flavicornis) shown below.
This is a very small and most unusual family with only 2 species resident in the UK. The picture below shows an underside view of The Festoon (Apoda limacodes) which has sucker-like structures in place of any prolegs.
There are 13 members of this family resident in the UK with 2 regular and 3 rare migrants. All have five pairs of prolegs and with the exception of the Purple Emperor (Apatura iris) they have spines of varying density. Those most often seen include the nettle feeding Small Tortoiseshell (Aglais urticae) and the Peacock (Inachis io) which are gregarious in their early stages and both resident in the UK. The Red Admiral (Vanessa atalanta) is also a nettle feeder and migrates to the UK every year, many adults also attempt to overwinter in the UK with varying success rates. The Red Admiral caterpillar feeds inside nettle leaves spun together. The other regular migrant to the UK is the Painted Lady (Vanessa cardui) whose larvae feed inside webs, their main foodplants being a range of thistles.
There are 6 members of this family resident in the UK and one regular migrant, the Clouded Yellow (Colias croceus), also a few other very rare migrants. The best known resident species are the cabbage feeding caterpillars of the Large White (Pieris brassicae) and the Small White (Pieris rapae). The Green-veined White (Pieris napi) is another well known butterfly whose larvae feed on Garlick and Hedge Mustard and other closely related plants. Also the Orange-tip (Anthocharis cardamines) whose larvae feed on the seed pods of Garlic Mustard and related Cruciferae.
There are 15 members of this family currently resident in the UK, all with woodlouse shaped caterpillars. The caterpillars are relatively small (10 to 17mm fully grown) and are usually only observed by those searching for them, or rearing them in captivity. Two examples are shown below, the Chalkhill Blue (Lysandra coridon) and the Small Copper (Lycaena phlaeas).
There are 11 species resident in the UK, the caterpillars all have five pairs of prolegs and feed on grasses mainly at night. The larvae are all green or brown, two examples being the Speckled Wood (Pararge aegeria) and the Marbled White (Melanargia galathea). They can be distinguished from other caterpillars with five pairs of prolegs by the presence of twin anal points as illustrated by the examples below.
There are 8 resident species of this family in the UK. The caterpillars of 6 species, such as the Silver-spotted Skipper (Hesperia comma) feed on a few grasses specific to each species. The other two species are the Dingy Skipper (Erynnis tages) which feeds on Bird's-foot Trefoil and Horseshoe Vetch and the Grizzled Skipper (Pyrgus malvae) which feeds on Wild Strawberry and a few other plants. The main features that may distinguish these from the caterpillars of other families are the semi-circular anal plate and their rather bulbous heads and 'baggy' bodies.
Sawfly larvae are often mistaken for Lepidoptera caterpillars so I have included details and pictures here which illustrate the main differences so you should be able to identify any species you find from either group. In most cases sawfly larvae have 6 or more pairs of abdominal prolegs so if the total number of pairs of true legs and prolegs is 9 or more then they are sawfly larvae. The pictures below illustrate examples of the sawfly larvae Craesus septentrionalis (left) and Craesus alniastri.
Apart from the difference in the number of pairs of prolegs the construction of caterpillar prolegs is significantly different from those of sawfly larvae. I think this is fairly obvious when comparing the examples from the two groups shown above. However another significant difference is that caterpillar prolegs have tiny hooks known as crochets on the underside of their claspers. The picture below illustrates the hooks which are visible on the last pair of prolegs of a Broad-bordered Bee Hawkmoth (Hemaris fuciformis) caterpillar.
THE CHRYSALIS OR PUPA AND EXAMPLES OF COCOONS
When a caterpillar is fully grown it usually changes colour when about to change into a chrysalis or pupa. This stage marks one of the most dramatic changes in the development of the insect. The pupal case is developed under the caterpillar's skin and the skin softens and splits to reveal the pupa underneath. The picture below shows a typical male Noctuid moth pupa and the areas where significant parts of the adult insect will form up within the pupa casing are clearly marked. The 3 pairs of legs (the true legs) are attached to the the thorax of the adult insect and from the front to the back of the head are named as follows:- The Prothoracic, the Mesothoracic and the Metathoracic legs.
When they are ready to pupate caterpillars look for a suitable place to complete this part of their life cycle which may be on a plant or tree, under leaf and other litter on the ground or in many cases under the earth.
Considering butterflies first, some butterfly caterpillars spin a silk pad on a leaf, plant stem or even a fence post. They then hold onto the silk pad with their hind (anal) claspers and hang, head down, waiting to change into a chrysalis. During the pupation process the skin of the caterpillar splits at the head end and the old skin is gradually worked up the body of the newly formed chrysalis until it is gathered at the top by the silk pad. At this stage hooks which have formed in the cremaster work their way outside the old skin and get a grip onto the silk pad. The chrysalis is now able to wriggle around until it has discarded the old skin and it remains hanging by the cremaster hooks whilst the chrysalis hardens and it remains suspended in this way until the butterfly eventually emerges.
Other butterfly species (for example, the Whites or Pierid species) suspend themselves the other way up, i.e. with their hind feet at the bottom with the head facing upwards. In these cases they need additional support so as well as a silk pad they spin an additional silk girdle around their 'middle' to keep themselves in the correct position whilst changing into a chrysalis. Examples of both suspension methods are shown in the picture below.
Some butterfly caterpillars which spend a relatively short time as chrysalis attach themselves to leaves and others that spend the winter as chrysalis pupate on the ground under plant litter etc. and may spin a loose cocoon around themselves.
The majority of moth caterpillars burrow underground and spin differing density cocoons around themselves before pupating. Some of those which overwinter as chrysalis spin cocoons on twigs, branches, leaves or even in plants such as heather. Two types of cocoon are shown in the picture below. The left hand picture illustrates the type spun by the Puss Moth (Cerura vinula) and 'kitten' caterpillars. These are very hard cocoons made up of silk and chewed bark - when the adult moth emerges it has to eject a liquid acid to soften an area of the cocoon before it can escape. The right hand cocoon is the shape of a cylindrical cigar tube which is constructed by the Oak Eggar (Lasiocampa quercus) and some other Eggar caterpillars (note that the fibers that normally attach the cocoon to the surrounding herbage have been removed). It is not a particularly hard cocoon and the adult moth is able to force its way out of one end when it emerges.
The picture below illustrates another type of cocoon which is in the shape of an upturned rowing boat. This cocoon was spun by a Green Silver-lines (Pseudoips prasinana) caterpillar and there are quite a few other caterpillar species that spin similar cocoons either on leaves or on twigs etc. In most cases there is an opening vertical split in the rear end of the boat which closes when the adult moth has escaped.
Finally, one of the most ingenious cocoons is the pear-shaped cocoon which is spun by the Emperor Moth (Saturnia pavonia) caterpillar. The picture below shows an Emperor Moth cocoon which has been cut in half so that you can see the way it is constructed. The caterpillar spins a neck at the top of the cocoon and within this a circle of fibres pointing upwards but not joined in the centre so that the moth can easily force its way through this one-way trap-door when it emerges. Perhaps the best 'engineer' of them all?
ADVANTAGES OF SEXING PUPAE
When breeding several generations of Lepidoptera in captivity in-breeding can result in weakened stock liable to disease and possibly in a high percentage of infertile eggs. To ensure brother and sister matings are avoided wherever possible it is best to ascertain the sex of each pupa and then keep male and female pupae in separate emerging cages. In this way different strains can be established and then cross-bred several generations later. If the species is found locally it is usually possible to attract males to an MV light trap or assemble them to a virgin female and hence introduce non-related stock for breeding purposes. The sex of most moth pupae and some butterfly pupae can be determined by visual inspection and examples on sexing pupae can be found by following this link.
THE ADULT BUTTERFLY OR MOTH
The drawing below illustrates the main elements of an adult butterfly. Most of the elements are obvious but where present in the adult butterfly or moth the palps are used for tasting and the proboscis for feeding on nectar and other liquids.