Every backyard east of the Rockies gets a cicada soundtrack in mid to late summer, and most years it comes from what people loosely call "dog-day" cicadas — a handful of green-and-black species in the genus Neotibicen that show up reliably every year without any synchronized event. Confusingly, those are also called annual cicadas, even though no individual actually lives just one year; it only looks that way because overlapping broods emerge every summer instead of all at once. That's a different animal entirely from the periodical cicadas in the genus Magicicada, which spend either 13 or 17 years underground and then erupt by the billions across a specific region in the same spring, all within a couple of weeks of each other.
Telling Them Apart at a Glance
Periodical cicadas are smaller and darker than the annual species, with a black body, orange-veined wings, and distinctive red eyes that make them easy to identify even from a few feet away. Annual dog-day cicadas run larger, with green or olive coloring and black eyes, and they call individually or in loose overlapping choruses rather than the wall-of-sound synchronized drone periodical broods produce. Timing is the other giveaway: annual cicadas peak in the heat of July and August, while periodical broods emerge earlier, typically in May, and are gone within about six weeks — a burst rather than a slow summer buildup.
Years Underground, Weeks in the Air
Both types spend the overwhelming majority of their lives as nymphs underground, tapping into tree roots and feeding on xylem fluid — a low-nutrient food source that's a big part of why development takes so long. Periodical nymphs track this underground for 13 or 17 years depending on the brood, apparently synchronizing emergence through some combination of counting seasonal cycles and sensing changes in root fluid as trees leaf out. Annual species take two to five years per individual, but because broods overlap, some nymphs are always finishing development in any given year, which is why the yard always has cicadas even though no single cicada is actually a year old.
When a nymph is finally ready, it digs an exit tunnel to the surface, sometimes leaving a distinctive turret of mud a few inches tall, and climbs the nearest vertical surface it can find — a tree trunk, a fence post, a porch railing. There it splits its nymphal skin down the back and emerges as a soft, pale adult, leaving behind the familiar brown, claw-footed exoskeleton (the exuvia) still gripping the bark. Wings pump full of fluid and harden over the following hours, and within a day or two the cicada has darkened to its adult coloring and joined the chorus.
Only male cicadas sing. A pair of ribbed membranes called tymbals, one on each side of the abdomen, buckle in and out rapidly when flexed by internal muscles, and the largely hollow abdomen acts as a resonating chamber that amplifies the clicks into the sustained buzz or whine people hear. Species can be told apart by pitch, rhythm, and whether the call rises, falls, or pulses — a skill that overlaps closely with the kind of ear-based identification covered in our guide to nighttime insect sounds, though cicadas themselves are strictly a daytime chorus.
Do They Actually Harm Trees?
Established, healthy trees tolerate cicadas fine; root feeding by nymphs over years causes negligible measurable damage, and the mass emergence itself doesn't threaten mature trees. The real risk is narrower: females cut slits into pencil-thin twigs to lay eggs, and on young, newly planted trees with mostly small-diameter branches, heavy egg-laying can cause enough twig dieback ("flagging," where the browned tip hangs on the branch) to stunt a sapling's growth for a season. Extension recommendations for periodical-cicada years generally suggest holding off on planting young trees until after a predicted emergence, or covering vulnerable saplings with fine netting rather than spraying, since insecticide does little against nymphs feeding safely underground and adult cicadas aren't around long enough for spraying to meaningfully reduce their numbers.
A Genuine Food Pulse
A periodical emergence dumps an enormous, short-lived protein source into the local food web all at once. Birds gorge on them, foxes and opossums eat them opportunistically right off the ground and low branches, and even fish key in on cicadas that fall into ponds and streams during the peak weeks. Predator populations can't meaningfully dent the sheer numbers involved — which is itself the evolutionary logic behind the strategy, overwhelming every predator in the area so enough individuals survive to reproduce regardless of how much gets eaten.