Decim Periodical Cicada

• Its mass emergence, at over a million insects per hectare, is a strategy of predator satiation.
• It feeds on xylem sap from tree roots as a nymph, and from branches as an adult.
• The adult lives only 4 to 6 weeks after 17 years underground as a nymph.
• It lives underground for seventeen years and emerges all at once, synchronised with millions of individuals of its own cohort, to breed and die within a few weeks.
• The strategy is called predator satiation: they emerge in such enormous densities that predators are sated long before they can finish them off, and it is enough for a sufficient number to survive.
• And it works because the number is prime. With 13 and 17 both prime cycles, the cohorts of different species hardly ever coincide — the 13- and 17-year ones only overlap once every 221 years — which avoids competition and accidental hybridisation.
• It also prevents any specialised predator from synchronising its own cycle with the cicada's: no predator can wait seventeen years.
• The individuals are slow, clumsy and easy to catch — just the opposite of what you would expect. At those densities, the individual risk is so low that investing in escape does not pay.
• The populations are organised into cohorts called broods, numbered with Roman numerals, each with its own emergence year and its own geographical area.
• They exist only in eastern North America; no other region of the world has periodical cicadas.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat & environment

Deciduous woodland of the central and eastern United States, the nymphs feeding underground on tree roots

Birth weight

A tiny newly hatched nymph, out of an egg laid on twigs

Size at birth

A tiny nymph on hatching from the egg

Sexual maturity

17 years, the age at which it emerges as a breeding adult

Gestation / incubation

A full nymphal cycle of 17 years underground, through several successive stages

Litter / clutch size

Hundreds of eggs laid on tree twigs by each female

Sources consulted: Animal Diversity Web; Britannica; Chicago Botanic Garden; Cicada Mania; Grokipedia (Magicicada septendecim); Penn State Extension; PMC (life-cycle control study, gut microbiome study)