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Insect mouthparts

A photograph of an adult damselfly eating an aphid

The biting mouthparts of an adult damselfly make short work of an aphid.

The 'primitive' arrangement of mouthparts is seen in the cockroach - here they are used for biting. There are five different structures which are used for the initial collection and processing of food:-

Diagram of mouthparts of a Cockroach

What are the different parts for?

  1. Labrum - a cover which may be loosely referred to as the upper lip.
  2. Mandibles - hard, powerful cutting jaws.
  3. Maxillae - 'pincers' which are less powerful than the mandibles. They are used to steady and manipulate the food. They have a five segmented palp which is sensory and often concerned with taste.
  4. Labium - the lower cover, often referred to as the lower lip. It actually represents the fused pair of ancestral second maxillae. They have a three segmented palp which is also sensory.
  5. Hypopharynx - a tongue-like structure in the floor of the mouth. The salivary glands discharge saliva through it.

This system remains little changed in all insects which chew their food, both larvae and adults. Where specialised food sources have been exploited, the mouthparts are modified, sometimes very considerably, so that the food may be obtained satisfactorily. Insect mouth parts show many cases of parallel evolution, the same end being independently achieved along similar, but not identical lines. Many insects take in liquid food. This is facilitated by the development of a sucking' arrangement from the mouthparts.

Mouthpart modifications

  1. Honey bee - the mandibles are very small and suitable for moulding wax, the labium is curved downwards and inwards forming a tube used for sucking up nectar.
    Illustration of honey bee mouthparts
  2. Butterflies and Moths - the mandibles have disappeared altogether. The maxillae are elongate, channelled along their surfaces and held together by hooks and spines to form a sucking tube. This proboscis may be very long, when not in use is carried coiled up like a watch spring under the head.
    Illustration of the mouthparts of Butterflies and Moths
  3. Diving beetle larvae - have a piercing and sucking arrangement. The mandibles are each curved over to form an almost closed groove along their inner surface. The prey is caught and pierced by the mandibles. Digestive juices are pumped down the groove. The food is made into a liquid. This semi-digested soup is sucked back up again through the groove.
    Illustration of mouthparts of Diving beetle larvae
  4. True bugs - these also have a piercing and sucking arrangement. The labium is elongated and acts as a sheath. This encloses the mandibles and maxillae which are modified as stylets for piercing. The maxillae have two tubes running along their length on the inside surface. 'Saliva' may be pumped down one of the tubes. This saliva makes the food into a liquid. The liquified food is sucked up the other tube.
    Illustration of mouthparts of true bugs
  5. House-fly - the proboscis shows a capillary mechanism. The labium is elongated and forms two lobes at the tip. These lobes have a series of fine tubes (pseudotracheae). The hypopharynx runs down the proboscis and digestive juices pass down this onto the food. The food is made into a liquid by these juices. This liquid is then drawn up the pseudotracheae by capillary action.
    Illustration of mouthparts of the housefly

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