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Insect Mouths Not Always Chewing Devices
My copy of Webster's New Collegiate Dictionary was published in 1961. I suppose having the word "new" in the title of a book that has been around almost 50 years is a bit misleading. But that well-used dictionary is still a good source for definitions of words. For instance, the word "mouth." Mouth is defined as "The opening through which an animal receives food; also, the cavity containing the tongue and teeth (when present) or the structures enclosing this cavity."
Of course, the word mouth is not always associated with animals. Jars, caves and rivers also have mouths. But to most of us, the mouth is that structure that our dentists call the oral cavity. It is the structure that we utilize for eating and talking and, on occasion, chewing gum or gasping for breath.
Mouths are not just human attributes. All animals including pigs, dogs, cows, birds, cats, snakes, fish and insects possess mouths. In general most animal mouths are similar: a box-like cavity with upper and lower jaws, more or less adorned with teeth. Such a mouth can be described as a biting, chewing type.
Chewing mouths of insects have two pair of mandible-like structures. The term mandible is used for one set; the other set are called maxillae. The maxillae are adorned with appendage-like structures called palps. But unlike mammal mandibles that function with an up-and-down motion, insect mandibles move from side to side.
This basic biting, chewing-type mouth is found in many kinds of insects. In fact, the most ancient of insects, including cockroaches and dragonflies, possess mouths of this type. Chewing mouths are also found in grasshoppers, crickets, katydids, beetles and praying mantids. In these insects both the adult and immature forms possess mouths of the biting, chewing kind.
Some types of insects have chewing-type mouths in the immature stage but another form of mouth as adults. For example, the familiar butterflies and moths have coiled, soda-straw-like mouths that are adapted for siphoning liquids. In the immature stage these scale-winged insects are known as caterpillars. Caterpillars have chewing mouths that they use to feed on plant tissue in such an efficient manner that some people dub caterpillars eating machines.
Some insects, such as honey bees, have mouths that include mandibles but also possess additional structures adapted for use in sucking up liquids. As a result honey bees can chew stuff such as wax but can also sip nectar from flowers or water from a stream. This type of insect mouth has been called a chewing-sucking mouth.
Insects that feed on liquids don't need to chew their food and, therefore, lack mandibles. Some common liquid-feeding insects are what are called the true bugs, such as boxelder bugs and stink bugs. Cicadas, leaf hoppers and plant hoppers also feed on liquid material, in this case plant sap. In order to access their liquid food these insects need to pierce plant tissue so their mouths are very much like hollow needles. These insect mouths are known as piercing-sucking mouths.
Mosquitoes also have what could be called a piercing-sucking mouth. In this case the mosquito pierces the skin of a victim and then sucks up blood. Not all mosquitoes, just female mosquitoes! Male mosquitoes don't feed on blood so their mouths are not adapted for blood sucking like the females of their kind.
The common house fly also feeds on liquids but has mouthparts described as of the sponging type. In this case the mouth is a tube to which is attached a sponge-like pad. The insect daubs the sponge onto surfaces of food items. If the food is liquid it is sopped up by the sponge and sucked into the insect. If the food is solid the old house fly just regurgitates some digestive juices in order to liquefy the food before sponging it up.
In the animal world chewing mouths seem to be the rule of thumb. Even in insects mouths adapted for chewing are common. But in the world of insect mouths there are also siphoning butterflies, chewing-lapping honey bees, piercing-sucking mosquitoes, and sponging house flies. Makes your jaw drop just to think about it, doesn't it?