Cicadas “eat” something called xylem (sap), which is a watery tree fluid containing amino acids and minerals. Cicadas drink rather than eat.
People probably ask “what do cicadas eat” because they are afraid that cicadas will eat their flowers and garden fruits and vegetables. Cicadas lack mouth parts that can chew and swallow vegetation. Your tomatoes and marigolds are safe.
How does a cicada drink xylem? The cicada’s mouth parts (aka rostrum or beak) are in the shape of a straw, which can pierce rootlets, roots and branches.
- The labium form the outside of the beak of the cicada; inside the labium is the stylet which is comprised of the mandibles and maxillae, which the cicada uses to pierce plants and drink their sap.
- The labrum connects the labium to the rostrum…
- The rostrum, or what people call the “nose” of the cicada, contains enourmous pumping muscles (1) that suck the xylem up into the cicada.
- The cicadas’s polymerized, viscous saliva plugs up any holes their mouth parts create (2), so a root will not continue to leak xylem when the cicada moves on to a new root. They put the cork back in the wine bottle, so to speak.
Cicadas are able to derive nutrition from the xylem thanks to bacterial endosymbionts that live in the cicada’s gut.
Cicada are known for drinking xylem from tree roots (as nymphs) and branches & twigs (as adults), however, when they are small they must rely on grasses, and possibly other small plants for nourishment.
- Young cicada nymphs are smaller than a grain of rice when they first begin feeding so the tiny roots of grasses are the best fit for their small beaks.
- Grass roots are likely the first roots a young cicada nymph will encounter, as they are close to the surface.
- Deciduous trees shed their rootlets in winter months, but grasses do not (2). This is not an issue in tropical regions.
Perhaps the reason why periodical cicadas are “attracted to woodland edges and exposed aspects, especially for chorusing and ovipositing” (1) is their offspring will be more likely to find grass roots in those areas. Young nymphs would be unlikely to find suitable tiny roots deep in a shady forrest.
Once the cicada nymph is larger, they can burrow to larger and more permanent tree roots, and feed from there.
It is interesting to note that not all cicadas feed on trees. Some feed on sugarcane, which is a giant grass (we’re back to the grasses again). The Brown sugarcane cicada (Cicadetta crucifera) and Yellow sugarcane cicada, (Parnkalla muelleri) of Australia feed on the sugarcane plants and cause damage to plants.
- 1 The Ecology, Behavior, And Evolution Of Periodical Cicadas, Kathy S. Williams and Chris Simon, Annu.Rev. Entomol. 1995. 40:269-95
- 2 Xylm Feeding by Periodical Cicada Nymphs on Pine and Grass Roots, With Novel Suggestions for Pest Control in Conifer Plantations and Orchards, Monte Lloyd and Joann White, OHIO J. SCI. 87 (3): 50-54, 1987