FAUNA PARAGUAY LEPIDOPTERA
Arguably the most distinctive of all insect groups, the Lepidoptera comprise the day-flying butterflies and the (usually!) night-flying moths. Lepidoptera is derived from the Greek and means "scale wing", in reference to the thousands of tiny, often brightly-coloured scales that line the wings of the insects in this group. This is the powder left on your fingers after handling a butterfly, commonly known as "butterfly dust". On this page you will find a basic introduction to the biology of this Insect order.
Butterflies have long been popular subjects for study due to their great diversity, visibility, aesthetic beauty and the ease with which they can be caught. Moths on the other hand, with their more muted, often cryptic colouration and night-flying habits have suffered from an image problem and a host of local legends have sprung up about them. Whilst the average butterfly is likely to be admired, their relatives the moths are often feared or despised. It is odd that this should be the case because the distinction between a butterfly and a moth is a completely artificial one. Taxonomically there are no characters that distinguish between a butterfly and a moth. It is all in our heads! Having said that we maintain the distinction here as most people are aware of the difference, even if they weren´t aware that the difference isn´t really a difference at all!
Lepidopterans undergo complete metamorphosis, a four-stage process - egg - larva - pupa - adult - that is described in more detail below. They have four wing, two large forewings and two smaller hind wings. Adults possess an elongated proboscis, an adaptation for sucking nectar, whilst larvae have highly-developed mouth parts for chewing plant matter.
PARTS OF A LEPIDOPTERAN
Like all insects the body of a Lepidopteran is divided into three sections - a small head, the thorax and an elongated abdomen. The outer casing of the body is the hard chitinous exoskeleton, to which the muscles and organs are attached internally.
The head consist of six sections, each with a sensory function. The large compound eyes dominate the head and are made up of as many as 17,000 individual optical units known as ommatidia. These provide the animal with excellent short range vision. Additionally a pair of "simple eyes" or ocelli are located at the back of the head, usually hidden beneath a covering of hairy scales. These are of uncertain function but may act as "range finders" or perhaps assist with object recognition at close quarters. The long antennae begin between the eyes and are usually simple with clubbed ends in butterflies, but often more complex and feathered in moths which rely less on visual stimuli due to their nocturnal habits. They are packed with delicate nerve cells which function as organs of smell as well as touch. The remaining three sections of the head are associated with the mouth parts, the most obvious being the long, tube-like proboscis which is coiled into a spiral when not in use. The mandibles are greatly reduced and Lepidopterans cannot bite, but the maxillaries are greatly enlarged resembling two half-tubes that unite to form the proboscis. Labial palps act as sensory ·"feelers".
The thorax is attached to the head via a membranous neck which allows the head to move side to side only. This section can be split into three segments - protothorax, mesothorax and metathorax - each with a pair of legs attached. The forewings are attached to the mesothorax and the hindwings to the metathorax, these two segments being firmly fused to provide additional support in flight. Two pairs of respiratory spiracles are located laterally on the thorax.
The legs are segmented. The coxa (or hip) is closest to the body and is attached to the femur via the trochanter (or femoral joint). The femur connects to the tibia, which in turn connects to the tarsus. The tarsus is made up of at least 5 small segments and has a clawed ending. These segments often have spines at the joints which enable the butterfly to support itself. Despite the similar names used to describe the parts of a butterfly leg, these structures are not homologous to those of vertebrates.
The most eyecatching feature of any Lepidopteran are the huge wings, the primary organs of locomotion. These consist of two flattened membranes joined together by connecting strands and traversed by a series of veins. The veins originate at the flat sclerites at the base of the wing, which in turn are attached to the musculature of the thorax and assist in wing movement. Veins are hollow and are filled with blood when the animal is alive. The two wings are joined along the basal edge, ensuring that they are fluttered simultaneously. In primitive species they are joined by a jugate, a membranous lobe protruding from the hind edge of the forewing and catching under the front edge of the hindwing. In most butterflies and moths however the wings are joined by a frenulum, a tuft of bristles which together form a flexible spine that hooks on to the hindwing. Wing form is variable, but tends to be narrower and more rounded in fast-fying species. As previously mentioned the wings are covered in scales that vary considerably in size and shape, from almost square, to scythe-shaped and even fan-like. Scales contain complex pigments which are responsible for the intricate matt colouration of many species. Glossy colouration is an artefact of light reflecting off the unevn surfaces of scales with a more complex structure.
The abdomen is elongated and soft and in Lepdiopetrans is broadly attached to the thorax. Typically it consists of 10 segments, with the last segments housing the sexual organs. Six or seven pairs of respiratory spiracles are located laterally. The digestive system, heart, excretory and reproductive organs and complex musculature are all located in this segment.
Internally Lepidopterans are relatively simple. A long tubular heart runs from the head along the length of the body cand arries blood. The thoracic section is known as the aorta and the abdominal section acts like a pump to feed the sensory organs of the head. The internal organs of the abdomen are bathed in blood, and this blood is sucked in through ostioles, lateral openings in the abdominal tubular heart, and pumped towards the head.
The oesophagus runs from the mouth, below the aorta to the abdomen, where the rest of the digestive system is located. Below this a nerve chord runs posteriorly, widening periodically into groups of ganglia - equivalent to brains. Generally speaking each section of the body has its own ganglia. Salivary glands located in the thorax are linked to the mouth parts.
In females the sexual organs dominate the abdominal cavity. This consists of a pair of ovaries, essentially egg-filled tubes. The eggs pass along the oviducts and into the vestibulum (where the two oviducts fuse), to await fertilisation by the male. Following fertilisation, and still in the vestibulum, the eggs becoming covered with a sticky secretion that enables them to be deposited onto plant surfaces. Male sexual organs consist of two fused testes where the sperms form, sperm ducts which transport the sperm, and a penis. The last 2 or 3 abdominal segments are highly modified into copulatory organs. Typically Lepidopterans become tightly fused during copulation and may remain "stuck together" for many hours.
LEPIDOPTERAN LIFE CYCLE
The Lepidopteran life cycle is composed of four distinct stages - egg - larva - pupa - adult. The individual stages are discussed in more detail below.
Egg (technically known as ova) size and number is generally specific, with size varting from 0.5mm to 3mm in diameter and number from 25 to as many as 10,000 depending on the species. Females of some species lay eggs singly, others in rows, and others in compact groups. Egg colour and shape varies widely, some are rounded, some tubular, some conical, and the surface of the egg under a microscope shows varied patterns of bands, hooks, pimples and spines. Colour frequently changes during development. At the top of the eggs is a shallow depression known as a micropyle, and in the centre of this is a tiny hole through which the sperm enters to fertilise the egg.
The coating of the egg is chitinous and is hard in some species, though softer in others. This enables the embryon to withstand harsh climactic conditions during its development. Though some species lay the eggs exposed, others cover them with a hairy coating in an effort to disguise them. Caterpillars may hatch in as little as three days, others spend long periods "hibernating" until conditions are right. Many caterpillars consume the egg shell upon hatching.
Lepidopteran larvae, commonly-known as caterpillars, are as variable as adults. However all are elongated, with soft bodies and a flexible skin. The body surface is covered with hair, sparse in some species, but well-developed in others. The distribution of hairs on a caterpillar´s body is known as chaetotaxy and is often useful in specific identification.
Internally caterpillars are arranged much like adult butterflies, however unlike adults the digestive system is much more prominent - caterpillars are essentially eating machines, designed to consume great quantities of plant matter and grow quickly - as a result the digestive pipe is greatly swollen. The reproductive organs are located towards the rear of the body, but are rudimentary and undeveloped.
The head is well-defined and hardened, equipped with powerful biting jaws. Six simple ocelli are located on either side of the mandibles, structurally similar to the ommatidia that will later make up the compund eye of the adult. Typically the body consists of 13 or 14 segments, the three segments closest to the head bearing a hardened leg joint that terminates in a claw - this will later become the thorax. The remaining segments will later form the abdomen and many are armed with "pro-legs" which end in a contractile pad surrounded by a ring of hooks. The last pair of pro-legs are known as "claspers".
Laterally the body is perforated with respiratory spiracles and the front part of the body is equipped with large salivary glands. The salivary duct lies between the mandibles at the base of the head and produces a liquid that solidifies to form silk in contact with air. This silk thread is important during pupation, when it may be used to "sew" leaves together and in some groups caterpillars "bungee jump" from a thread of this silk to escape enemies.
Caterpillars may shed their skin and thus increase their size four or five times before pupation. With each moulting the colour or appearance may also change. At the end of development the caterpillar empties its gut, stops feeding and prepares to pupate.
The adult form develops within the confines of the pupa, generally a hrad-surfaced, oval-shaped structure with a narrow tip. The animal does not moult or feed whilst in this stage, though it may move occasionally within the pupa. Breathing is via laterally-located spiracles, one pair located in the thorax and one pair for each abdominal segment.
Development involves the liquefication of internal organs (histolysis) and requires specific temperatures at specific times in the development. The position of the internal organs remains essentially the same, but they undergo considerable re-organisation to cope with the differing needs of the adult form. The external appearance of the butterfly is usually visible on the surface of the pupa. The head and thorax are immobile, but the abdominal segments are capable of slight side to side movement. Butterfly pupae are often ornately-decorated, with hollows, grooves and horns assisting in camouflage. Some species pupate underground, within rotting wood or, more typically in exposed areas suspended from hooks situated at the tips of the pupa - known as the cremaster. Pupae can be sexed by examining the tail end of the pupa, males have a shorter margin between the anal and genital openings than females.
Whn ready to emerge the imago makes a small hole in the head end and inhales deeply, the influx of air splitting the cocoon and allowing the adult to emerge. Once it forms a grip with the legs it extracts the crumpled, soft wings. The animal then has to pump blood into the veins of the wings to expand them to their full size so that they may harden and be ready for flight. Upon completion the fresh adult ejects excretory products stored in the Malpighian tubules, squirting a pinkish liquid known as meconium from the abdomen, and it is ready to take its first flight. Freshly-emerged adults that are disturbed before the wings have dried may prematurely excrete the meconium and fail to complete their development.
Lepidopterans belong to the Class Insecta and the sub-class Pterygota (winged insects). They are included in the supra-order Panorpoidea along with Lacewings (Planipennia), Scorpion Flies (Mecoptera), True Flies (Diptera) and Fleas (Siphanoptera) amongst others.
Click here for access to the Butterfly Image Gallery and familial accounts.
Click here for access to the Moth Image Gallery and familial accounts.
Many thanks to Kim Garwood, Ezequiel Osvaldo Núñez Bustos, Richard Lindstrom, Ulf Drechsler and Ian Kitching
for their assistance with Lepidopteran matters.
Designed by Paul Smith 2006. This website is copyrighted by law. Material contained herewith may not be used without the prior written permission of FAUNA Paraguay. Photographs on this web-site were taken by Paul Smith, Hemme Batjes, Regis Nossent,
Alberto Esquivel, Arne Lesterhuis, José Luis Cartes, Rebecca Zarza and Hugo del Castillo and are used with their permission.