Cicadas are one of the loudest and most noticeable insects, and their sudden, synchronized appearances often spark curiosity about their basic biology. While they do not have a typical chewing mouth like a grasshopper, cicadas possess a highly specialized feeding structure to access their unique diet. This specialized apparatus allows them to acquire the necessary fluids from plants, which is a process entirely separate from the iconic noise they produce.
The Specialized Feeding Apparatus
Cicadas belong to the insect order Hemiptera, commonly known as true bugs, which are characterized by their piercing-sucking mouthparts. The structure that serves as the cicada’s mouth is a complex, jointed tube called a rostrum, or sometimes referred to as a proboscis. This beak-like sheath projects from the underside of the head and is typically tucked between the legs when the insect is not feeding.
Encased within the protective outer sheath of the rostrum are four needle-like filaments known as stylets. Two of these stylets are derived from the insect’s mandibles, and the other two from the maxillae, which fit together precisely. This arrangement forms two separate channels: a food canal for ingesting fluids and a salivary canal for injecting digestive enzymes. The entire apparatus is designed not for chewing solid material but for penetrating plant tissue to extract liquid sustenance.
The Mechanism of Cicada Feeding
The cicada’s diet consists exclusively of xylem sap. To reach this liquid, the cicada projects its stylets deep into the plant, piercing the exterior bark and accessing the xylem vessels. Both nymphs feeding underground on tree roots and adults feeding on above-ground branches utilize this same piercing technique.
Xylem sap is extremely dilute, composed of about 99% water with very low concentrations of nutrients like amino acids and carbohydrates. Because this fluid is under negative pressure, the cicada must use powerful pumping muscles located in its head to generate the suction required to draw the sap into its body. To compensate for the low nutritional value of this diet, cicadas rely on symbiotic bacteria housed within specialized cells to synthesize essential amino acids. This reliance on a nutrient-poor source necessitates constant feeding to obtain adequate energy for growth and development.
Distinguishing Sound Production from Feeding
The loud, buzzing sound that makes cicadas famous is frequently mistaken for a function of their mouth, but the mechanism is entirely separate from their feeding apparatus. The sound is produced by specialized organs called tymbals, located on the sides of the male cicada’s abdomen.
Each tymbal is a ribbed membrane that is rapidly flexed inward by a powerful internal muscle. As the membrane buckles, it produces rapid clicks that combine to form the continuous sound. The male cicada’s abdomen is largely hollow, acting as a resonance chamber to amplify the noise, which can reach over 100 decibels in some species. This acoustic signal serves two primary purposes: attracting mates and acting as a defense or alarm call. The sound is a form of communication, while the rostrum is strictly for plant fluid consumption.