page_title: External morphology of Lepidoptera
section_title: Mouthparts
hierarchical_section_title: External morphology of Lepidoptera / Head / Mouthparts
caption_attribution_description: This is a butterfly proboscis (galea), which is often referred to as a "tongue". The proboscis is about 100um (0.1mm) thick. This was photographed using a DSLR attached to a compound microscope with a Nikon M Plan 40x/0.5 lens. Specimen from a commercially prepared slide. This is a z-stack of 28 images processed with Zerene Stacker.
context_page_description: The external morphology of Lepidoptera is the physiological structure of the bodies of insects belonging to the order Lepidoptera, also known as butterflies and moths. Lepidoptera are distinguished from other orders by the presence of scales on the external parts of the body and appendages, especially the wings. Butterflies and moths vary in size from microlepidoptera only a few millimetres long, to a wingspan of many inches such as the Atlas moth. Comprising over 160,000 described species, the Lepidoptera possess variations of the basic body structure which has evolved to gain advantages in adaptation and distribution.
  Lepidopterans undergo complete metamorphosis, going through a four-stage life cycle: egg, larva or caterpillar, pupa or chrysalis, and imago / adult. The larvae – caterpillars – have a toughened head capsule, chewing mouthparts, and a soft body, that may have hair-like or other projections, three pairs of true legs, and up to five pairs of prolegs. Most caterpillars are herbivores, but a few are carnivores or detritivores.
context_section_description: While mandibles or jaws (chewing mouthparts) are only present in the caterpillar stage, the mouthparts of most adult Lepidoptera mainly consist of the sucking kind; this part is known as the proboscis or haustellum. A few Lepidoptera species have reduced mouthparts and do not feed in the adult state. Others, such as the basal family Micropterigidae, have chewing mouthparts.
  The proboscis (plural – proboscises) is formed from maxillary galeae and is adapted for sucking nectar. It consists of two tubes held together by hooks and separable for cleaning. Each tube is inwardly concave, thus forming a central tube up which moisture is sucked. Suction is effected through the contraction and expansion of a sac in the head. The proboscis is coiled under the head when the insect is at rest and extended only when feeding. The maxillary palpi are reduced and even vestigial. They are conspicuous and five segmented in some of the more basal families and are often folded.
  The shape and dimensions of the proboscis have evolved to give different species a wider and therefore more advantageous diet. There is an allometric scaling relationship between body mass of Lepidoptera and length of proboscis from which an interesting adaptive departure is the unusually long-tongued sphinx moth Xanthopan morganii praedicta. Charles Darwin predicted the existence and proboscis length of this moth before its discovery based on his knowledge of the long-spurred Madagascan star orchid Angraecum sesquipedale.
  There are primarily two feeding guilds in Lepidoptera – the nectarivorous who obtain the majority of their nutritional requirements from floral nectar and those of the frugivorous guild who feed primarily on juices of rotting fruit or fermenting tree sap. There are substantial differences between the morphology of the proboscises of both feeding guilds. Hawkmoths (family Sphingidae) have elongated proboscises which enable them to feed on and pollinate flowers with long tubular corrollas. Besides this, a number of taxa (especially noctuid moths) have evolved different proboscis morphologies. Certain noctuid species have developed piercing mouthparts; the proboscis has sclerotised scales on the tip with which to pierce and suck blood or fruit juices. Proboscises in some Heliconius species have evolved to consume solids such as pollen. Some other moths, mostly noctuids, have modified proboscises to suit their mode of nutrition – lachrymophagy (feeding on tears of sleeping birds). The proboscises often have sharp apices as well as a host of barbs and spurs on the stem.
caption: Butterfly proboscis, showing the structure of the two galeae that comprise it.
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