Ecdysis is the moulting of the cuticle in many invertebrates of the clade Ecdysozoa. Since the cuticle of these animals typically forms a largely inelastic exoskeleton, it is shed during growth and a new, larger covering is formed.[1] The remnants of the old, empty exoskeleton are called exuviae.[2]

After moulting, an arthropod is described as teneral, a callow; it is "fresh", pale and soft-bodied. Within one or two hours, the cuticle hardens and darkens following a tanning process analogous to the production of leather.[3] During this short phase the animal expands, since growth is otherwise constrained by the rigidity of the exoskeleton. Growth of the limbs and other parts normally covered by hard exoskeleton is achieved by transfer of body fluids from soft parts before the new skin hardens. A spider with a small abdomen may be undernourished but more probably has recently undergone ecdysis. Some arthropods, especially large insects with tracheal respiration, expand their new exoskeleton by swallowing or otherwise taking in air. The maturation of the structure and colouration of the new exoskeleton might take days or weeks in a long-lived insect; this can make it difficult to identify an individual if it has recently undergone ecdysis.

Ecdysis allows damaged tissue and missing limbs to be regenerated or substantially re-formed. Complete regeneration may require a series of moults, the stump becoming a little larger with each moult until it is a normal, or near normal, size.[4]

Rhopalomyia solidaginis eclosion
Adult Rhopalomyia solidaginis fly, emerging from pupal case
Cicada molting animated-2
Process of ecdysis of a cicada.


The term ecdysis comes from Ancient Greek: ἐκδύω (ekduo), "to take off, strip off".[5]


In preparation for ecdysis, the arthropod becomes inactive for a period of time, undergoing apolysis or separation of the old exoskeleton from the underlying epidermal cells. For most organisms, the resting period is a stage of preparation during which the secretion of fluid from the moulting glands of the epidermal layer and the loosening of the underpart of the cuticle occur. Once the old cuticle has separated from the epidermis, a digesting fluid is secreted into the space between them. However, this fluid remains inactive until the upper part of the new cuticle has been formed. Then, by crawling movements, the organism pushes forward in the old integumentary shell, which splits down the back allowing the animal to emerge. Often, this initial crack is caused by a combination of movement and increase in blood pressure within the body, forcing an expansion across its exoskeleton, leading to an eventual crack that allows for certain organisms such as spiders to extricate themselves. While the old cuticle is being digested, the new layer is secreted. All cuticular structures are shed at ecdysis, including the inner parts of the exoskeleton, which includes terminal linings of the alimentary tract and of the tracheae if they are present.



Moulting (ecdysis) in southern hawker, Aeshna cyanea
Moulting (ecdysis) in southern hawker, Aeshna cyanea

Each stage of development between moults for insects in the taxon endopterygota is called an instar, or stadium, and each stage between moults of insects in the Exopterygota is called a nymph: there may be up to 15 nymphal stages. Endopterygota tend to have only four or five instars. Endopterygotes have more alternatives to moulting, such as expansion of the cuticle and collapse of air sacs to allow growth of internal organs.

The process of moulting in insects begins with the separation of the cuticle from the underlying epidermal cells (apolysis) and ends with the shedding of the old cuticle (ecdysis). In many species it is initiated by an increase in the hormone ecdysone. This hormone causes:

  • apolysis – the separation of the cuticle from the epidermis
  • secretion of new cuticle materials beneath the old
  • degradation of the old cuticle

After apolysis the insect is known as a pharate. Moulting fluid is then secreted into the exuvial space between the old cuticle and the epidermis, this contains inactive enzymes which are activated only after the new epicuticle is secreted. This prevents the new procuticle from getting digested as it is laid down. The lower regions of the old cuticle, the endocuticle and mesocuticle, are then digested by the enzymes and subsequently absorbed. The exocuticle and epicuticle resist digestion and are hence shed at ecdysis.


Crab spider female in ecdysis; Genus Synema, Family Thomisidae 5725s
Female crab spider Synema decens, teneral after final ecdysis, still dangling from drop line, about to be mated, opisthosoma still shrunken

Spiders generally change their skin for the first time while still inside the egg sac, and the spiderling that emerges broadly resembles the adult. The number of moults varies, both between species and genders, but generally will be between five times and nine times before the spider reaches maturity. Not surprisingly, since males are generally smaller than females, the males of many species mature faster and do not undergo ecdysis as many times as the females before maturing. Members of the Mygalomorphae are very long-lived, sometimes 20 years or more; they moult annually even after they mature.

Spiders stop feeding at some time before moulting, usually for several days. The physiological processes of releasing the old exoskeleton from the tissues beneath typically cause various colour changes, such as darkening. If the old exoskeleton is not too thick it may be possible to see new structures, such as setae, from outside. However, contact between the nerves and the old exoskeleton is maintained until a very late stage in the process.

The new, teneral exoskeleton has to accommodate a larger frame than the previous instar, while the spider has had to fit into the previous exoskeleton until it has been shed. This means the spider does not fill out the new exoskeleton completely, so it commonly appears somewhat wrinkled.

Most species of spiders hang from silk during the entire process, either dangling from a drop line, or fastening their claws into webbed fibres attached to a suitable base. The discarded, dried exoskeleton typically remains hanging where it was abandoned once the spider has left.

To open the old exoskeleton, the spider generally contracts its abdomen (opisthosoma) to supply enough fluid to pump into the prosoma with sufficient pressure to crack it open along its lines of weakness. The carapace lifts off from the front, like a helmet, as its surrounding skin ruptures, but it remains attached at the back. Now the spider works its limbs free and typically winds up dangling by a new thread of silk attached to its own exuviae, which in turn hang from the original silk attachment.

At this point the spider is a callow; it is teneral and vulnerable. As it dangles, its exoskeleton hardens and takes shape. The process may take minutes in small spiders, or some hours in the larger Mygalomorphs. Some spiders, such as some Synema species, members of the Thomisidae (crab spiders), mate while the female is still callow, during which time she is unable to eat the male.[6]


Eurypterids are a group of chelicerates that became extinct in the late Permian. They underwent ecdysis similarly to extant chelicerates, and most fossils are thought to be of exuviae, rather than cadavers.[2]

See also


  1. ^ John Ewer (2005). "How the ecdysozoan changed its coat". PLoS Biology. 3 (10): e349. doi:10.1371/journal.pbio.0030349. PMC 1250302. PMID 16207077.
  2. ^ a b O. Erik Tetlie, Danita S. Brandt & Derek E. G. Briggs (2008). "Ecdysis in sea scorpions (Chelicerata: Eurypterida)". Palaeogeography, Palaeoclimatology, Palaeoecology. 265 (3–4): 182–194. doi:10.1016/j.palaeo.2008.05.008.
  3. ^ Russell Jurenka (2007). "Insect physiology". In Sybil P. Parker. McGraw-Hill Encyclopedia of Science & Technology. 9 (10th ed.). p. 323. ISBN 978-0-07-144143-8.
  4. ^ Penny M. Hopkins (2001). "Limb regeneration in the fiddler crab, Uca pugilator: hormonal and growth factor control". American Zoologist. 41 (3): 389–398. doi:10.1093/icb/41.3.389.
  5. ^ Liddell & Scott (1889). An Intermediate Greek-English Lexicon. Oxford: Clarendon Press.
  6. ^ Erik Holm & Anna Sophia Dippenaar-Schoeman (2010). Goggo Guide: the Arthropods of Southern Africa. LAPA. ISBN 978-0-7993-4689-3.

External links

  • Media related to Ecdysis at Wikimedia Commons
Amblyomma variegatum

Amblyomma variegatum, commonly known as the tropical bont tick, is a species of tick of the genus Amblyomma endemic to Africa. It has spread from its centre of origin to several countries, including the Caribbean islands, where it is known as the Senegalese tick (due to the suspected introduction of the tick from cattle imports from that country) and the Antigua gold tick. They are vividly coloured (especially the males) and have a substantial impact on livestock, primarily through their transmission of diseases. They are three-host hard ticks (where each life stage completes a blood meal on a particular host before dropping-off and ecdysis) that have been found on a variety of domesticated species such camels, cattle, goats, sheep, dogs, and various species of wildlife.


Apolysis (Ancient Greek: ἀπόλυσις "discharge, lit. absolution") is the separation of the cuticle from the epidermis in arthropods and related groups (Ecdysozoa). Since the cuticle of these animals is also the skeletal support of the body and is inelastic, it is shed during growth and a new covering of larger dimensions is formed. During this process, an arthropod becomes dormant for a period of time. Enzymes are secreted to digest the inner layers of the existing cuticle, detaching the animal from the outer cuticle. This allows the new cuticle to develop without being exposed to the environmental elements.After apolysis, ecdysis occurs. Ecdysis is the actual emergence of the arthropod into the environment and always occurs directly after apolysis. The newly emerged animal then hardens and continues its life.

Arthropod exoskeleton

Arthropods are covered with a tough, resilient integument or exoskeleton of chitin. Generally the exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. This happens in parts of the body where there is a need for rigidity or elasticity. Typically the mineral crystals, mainly calcium carbonate, are deposited among the chitin and protein molecules in a process called biomineralization. The crystals and fibres interpenetrate and reinforce each other, the minerals supplying the hardness and resistance to compression, while the chitin supplies the tensile strength. Biomineralization occurs mainly in crustaceans; in insects and Arachnids the main reinforcing materials are various proteins hardened by linking the fibres in processes called sclerotisation and the hardened proteins are called sclerotin.

In either case, in contrast to the carapace of a tortoise or the cranium of a vertebrate, the exoskeleton has little ability to grow or change its form once it has matured. Except in special cases, whenever the animal needs to grow, it moults, shedding the old skin after growing a new skin from beneath.


The brille (also called the ocular scale, eye cap or spectacle) is the layer of transparent, immovable disc-shaped skin or scale covering the eyes of some animals for protection, especially in animals without eyelids. The brille has evolved from a fusion of the upper and lower eyelids. Brille means "spectacles" or "glasses" in German, Norwegian and Danish and "shine" in French and Spanish.

In snakes, there are no eyelids and the brille is clear and cannot be distinguished, except when the animal is becoming ready for ecdysis. At that time, it becomes cloudy and is visible as a cover over the eye. When the snake moults, the brille is also shed, generally inside out, as part of its skin. The brilles protect their eyes from dust and dirt and give them a "glassy-eyed" blank appearance.Snakes, flap-footed lizards, night lizards, and some skinks have brilles. All geckos except those in the subfamily Eublepharinae (eyelid geckos) possess brilles.

Some groups of bony fish have a transparent eyelid known as the adipose eyelid. Some reptiles, mammals and birds have a translucent third eyelid that moves horizontally across the eye called the nictitating membrane.

Ecdysis (album)

Ecdysis is Miho Hatori's first solo album after a series of contributions to diverse bands, including Cibo Matto, Gorillaz, the Beastie Boys, and Smokey & Miho. It was released on October 21, 2005 in Japan under the Speedstar International label. The album was distributed in the United States one year later under the Rykodisc label.

Ecdysis (disambiguation)

Ecdysis is the moulting of the exoskeleton in arthropods and other animals.

Ecdysis may also refer to:

Ecdysis (album), an album by Miho Hatori


Ecdysozoa () is a group of protostome animals, including Arthropoda (insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes. A large study in 2008 by Dunn et al. strongly supported the Ecdysozoa as a clade, that is, a group consisting of a common ancestor and all its descendants.The group is also supported by morphological characters, and includes all animals that grow by ecdysis, moulting their exoskeleton.

The group was initially contested by a significant minority of biologists. Some argued for groupings based on more traditional taxonomic techniques, while others contested the interpretation of the molecular data.


Eleuteroschisis is asexual reproduction in dinoflagellates in which the parent organism completely sheds its theca (i.e. undergoes ecdysis) either before or immediately following cell division. Neither daughter cell inherits part of the parent theca.

In terms of asexual division of motile cells, desmoschisis is generally the case in gonyaulacaleans whereas eleutheroschisis is generally the case in peridinialeans.

Grass snake

The grass snake (Natrix natrix), sometimes called the ringed snake or water snake, is a Eurasian non-venomous snake. It is often found near water and feeds almost exclusively on amphibians. The barred grass snake, Natrix helvetica, was split off as a separate species in 2017.


Homolodromiidae is a family of crabs, the only family in the superfamily Homolodromioidea. In contrast to other crabs, including the closely related Homolidae, there is no strong linea homolica along which the exoskeleton breaks open during ecdysis. The family comprises two genera, Dicranodromia, which has 18 species, and Homolodromia, with five species.


In biology, the imago is the last stage an insect attains during its metamorphosis, its process of growth and development; it also is called the imaginal stage, the stage in which the insect attains maturity. It follows the final ecdysis of the immature instars.In a member of the Ametabola or Hemimetabola, in which metamorphosis is "incomplete", the final ecdysis follows the last immature or nymphal stage.

In members of the Holometabola, in which there is a pupal stage, the final ecdysis follows emergence from the pupa, after which the metamorphosis is complete, although there is a prolonged period of maturation in some species.The imago is the only stage during which the insect is sexually mature and, if it is a winged species, has functional wings. The imago often is referred to as the adult stage.Members of the order Ephemeroptera (mayflies) do not have a pupal stage, but they briefly pass through an extra winged stage called the subimago. Insects at this stage have functional wings but are not yet sexually mature.The Latin plural of imago is imagines, and this is the term generally used by entomologists –

however, imagoes is also acceptable.


An instar ( (listen), from the Latin "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (ecdysis), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, changes in the number of body segments or head width. After moulting, i.e. shedding their exoskeleton, the juvenile arthropods continue in their life cycle until they either pupate or moult again. The instar period of growth is fixed; however, in some insects, like the salvinia stem-borer moth, the number of instars depends on early larval nutrition. Some arthropods can continue to moult after sexual maturity, but the stages between these subsequent moults are generally not called instars.

For most insect species, an instar is the developmental stage of the larval forms of holometabolous (complete metamorphism) or nymphal forms of hemimetabolous (incomplete metamorphism) insects, but an instar can be any developmental stage including pupa or imago (the adult, which does not moult in insects).

The number of instars an insect undergoes often depends on the species and the environmental conditions, as described for a number of species of Lepidoptera. However it is believed that the number of instars can be physiologically constant per species in some insect orders, as for example Diptera and Hymenoptera. It should be minded that the number of larval instars is not directly related to speed of development. For instance, environmental conditions may dramatically affect the developmental rates of species and still have no impact on the number of larval instars. As examples, lower temperatures and lower humidity often slow the rate of development- an example is seen in the lepidopteran tobacco budworm and that may have an effect on how many molts will caterpillars undergo. On the other hand, temperature is demonstrated to affect the development rates of a number of hymenopterans without affecting numbers of instars or larval morphology, as observed in the ensign wasp and in the red imported fire ant . In fact the number of larval instars in ants has been the subject of a number of recent investigations , and no instances of temperature-related variation in numbers of instars have yet been recorded .

Ivan Regen

Ivan (Janez) Regen (known also as Johann Regen) (December 9, 1868 – July 27, 1947) was a Slovenian biologist, best known for his studies in the field of bioacoustics.

Regen was born in the hamlet of Lajše (today part of Gorenja Vas, Slovenia) and became interested in insect sounds as a child. His family couldn't afford to pay for his schooling, so he studied first at the local seminary for which he received a scholarship, and slowly saved enough funds for the tuition fee in Vienna. There he studied natural history at the University of Vienna under the tutorship of Grobben, Exner and Claus. He received his doctorate in 1897 and began to work as a gymnasium professor, first in Vienna, and later in Hranice (Moravia). At last he was transferred back to a gymnasium in Vienna after a recommendation from Exner and worked there until his retirement in 1918.In the meantime Regen began his research in animal physiology, being one of the first Slovenian scientists to work abroad after the World War I. With careful observations of katydid and cricket stridulation he proved that insects respond to acoustic stimuli from other individuals and was able to provoke his subjects to respond to artificial stimulation using a loudspeaker. Later, he demonstrated that insect hearing depends on intact tympanal organ which was the first description of this organ's function. For his contributions he is regarded as the founder of modern bioacoustics. He also studied other physiological phenomena in insects, such as breathing, hibernation, the development of pigment under different conditions, and ecdysis.Regen's largest project was a so-called "geobiological laboratory", a large terrarium in which he studied phonotaxis on a large scale. Using as many as 1600 females with intact or damaged hearing organs, he was able to statistically evaluate their behaviour.He was a private researcher since 1911, but remained in touch with Slovenia, supporting several local societies and cultural institutions, and establishing Slovene terminology for the fields he worked in. In 1921, he declined the invitation to become a professor at the University of Ljubljana. In 1940, he became an associate member of Slovenian Academy of Sciences and Arts and was also an honorary member of Slovenian society of natural history.


The Laboulbeniomycetes are a unique group of fungi that are apparent external parasites of insects and other arthropods, both terrestrial and aquatic. These fungi are minute; their fruiting bodies commonly measure less than one millimeter. They live on the antennae, the mouthparts or other body regions of their arthropod hosts. Although several species of Laboulbeniomycetes have more or less extensive, root-like hyphal systems (haustoria) inside their hosts, as a group these fungi are apparently harmless to the animals they live on. These fungi are usually apparent only on adult hosts; apparently immature arthropods eliminate them during ecdysis (adult arthropods no longer molt). Some fungi in the Laboulbeniomycetes have separate female and male individuals, like Herpomyces.

In the micrograph to the right, two flask-shaped, about 0.3 mm long female fruiting bodies of Herpomyces periplanetae can be seen. They are full of ascospores. Between them, there are two short, finger-like male individuals. Below, a part of a striated foot cell is visible. In nature, the fruiting bodies sit on the foot cell, which lies on the insect's antennae. Herpomyces periplanetae is a very widespread parasite on the antennae of adult cockroaches in the genus Periplaneta, like the common American cockroach, Periplaneta americana.


Microdictyon is an extinct "armored worm" coated with net-like scleritic scales, known from the Early Cambrian Maotianshan shale of Yunnan China. Microdictyon is sometimes included in a somewhat ill-defined Phylum – Lobopodia – that includes several other odd worm-like and segmented free-swimming animals that do not appear to be arthropods or worms. The phylum includes Microdictyon, Onychodictyon, Cardiodictyon,

Luolishania, Paucipodia, as well as the Anomalocaridids. The isolated sclerites of Microdictyon are known from other Lower Cambrian deposits. Microdictyon sclerites appear to have moulted; one sclerite seems to have been preserved during ecdysis.Microdictyon sinicum (Chen, Hou and Lu, 1989) is typical. The wormlike animal has ten pairs of sclerites (suggestions that these may be eyes or eye-like structures have no weight) on the sides, matched to a pair of tentacle-like feet below. The head and posterior are tubular and featureless.

Moult (disambiguation)

Moult or molt (see spelling differences) may have several meanings:

Moulting, the manner in which an animal routinely casts off a part of its body (often, but not always, an outer layer or covering)

Ecdysis, the shedding of the exoskeleton in arthropods and other invertebrates

Exuvia, the old skeleton shed during ecdysis

Moult, Calvados, a French town


In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer layer or covering), either at specific times of the year, or at specific points in its life cycle.

Moulting can involve shedding the epidermis (skin), pelage (hair, feathers, fur, wool), or other external layer. In some groups, other body parts may be shed, for example, wings in some insects or the entire exoskeleton in arthropods.


Olenellina is a suborder of the order Redlichiida of Trilobites that occurs about halfway during the Lower Cambrian, at the start of the stage called the Atdabanian. The earliest trilobites in the fossil record are arguably Olenellina, although the earliest Redlichiina and Eodiscina follow quickly. The suborder died out when the Lower passed into the Middle Cambrian, at the end of the stage called Toyonian. A feature uniting the Olenellina is the lack of rupture lines (or sutures) in the headshield, which in other trilobites assist the periodic moulting (or ecdysis), associated with arthropod growth. Some derived trilobites have lost facial sutures again (some Eodiscina, all Agnostina, and a few Phacopina), but all of these are blind, while all Olenellina have eyes.

Reptile scale

Reptile skin is covered with scutes or scales which, along with many other characteristics, distinguish reptiles from animals of other classes. Scales are made of alpha and beta-keratin and are formed from the epidermis (contrary to fish, in which the scales are formed from the dermis). They may be ossified or tubercular, as in the case of lizards, or modified elaborately, as in the case of snakes.

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