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Many species sleep for an entire season or travel from one continent to another every year. For all species I know all of these recurring events occur in a period of one year. One might refer to these species as 1-year-cycle species.

I wonder whether there are any 2-year cycle species. For example one that travels to some place not every but only every other year or sleeps for an entire year, before becoming active again.

I don't know any and I just started to wonder whether there is an evolutionary argument for this.

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    $\begingroup$ There are some polar/high altitude animal species (insects IIRC) that will hibernate until conditions are right, sometimes more than 1 year. $\endgroup$
    – bob1
    May 12, 2022 at 20:07
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    $\begingroup$ Welcome to Biology.SE. Are we to assume you are only interested in animals? Are you interested in examples like @bob1 suggests where organisms have prolonged often highly variable dormant periods? Please edit your post to answer these questions, and also tell us where you've looked for answers, what you do know about the topic, and where exactly you still have questions. Please take the tour and consult the help center starting with How to Ask for details. $\endgroup$
    – tyersome
    May 12, 2022 at 20:48
  • $\begingroup$ Are you aware of insects that have 2, 4 and even 9 year cycles, some of which swarm regularly with many years interval? $\endgroup$ May 13, 2022 at 8:54
  • $\begingroup$ Interesting, thanks for pointing this out! But @LifeInTheTrees this is very much answering the question, as it is a periodic process. Can you maybe provide the name of the species and I'll accept the answer $\endgroup$ May 13, 2022 at 10:18
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    $\begingroup$ Biennial plants come to mind. There's also 2-year cicadas. (There's also 13 and 17 year cycles -- periodic cicadas (see biology.stackexchange.com/a/100721/16866 and biology.stackexchange.com/a/9241/16866)) $\endgroup$ May 14, 2022 at 1:53

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biennial migration

In sharks (Naidoo et al. 2017):

C. taurus females undertake a biennial migration along the east coast of SA of approximately 1000 km from their gestation grounds to their pupping grounds in the south, so they are not exposed to any single point source of pollution such as a marine outfall or an industrialised harbour for lengthy periods.

biennial life cycles

Semivoltine, biennial are good search terms for answering this question, e.g.: https://scholar.google.com/scholar?q=semivoltine+biennial

As other answers have suggested, most of the examples we find this way are insects living in relatively cold environments where it may take more than one year to complete a life cycle (I haven't come across any examples where the life cycle is always biennial — generally these species have univoltine (one generation per year) or faster life cycles in warmer climates and semivoltine/biennial cycles in colder climates.

e.g. Sota 1996:

Two closely related Leptocarabus [beetle] species overwintered as larvae in the first winter and as adults in the second and later years; one species occurred at altitudes from 750 to 2200 m, and its life cycle changed from annual to biennial in the subalpine zone. The other smaller species occurred from subalpine to alpine zones and had a biennial life cycle.

evolutionary argument

This is somewhat hand-wavy, but it appears that most examples of biennial life cycles/migration occur in organisms with sufficiently rates of growth (in the case of insects) or resource acquisition (in the case of sharks) that they cannot manage to complete their life cycle or reproduce in a single year, so must delay until a second year. (These organisms also live in environments that are sufficiently seasonal that they must synchronize with the annual cycle in some way.)


Naidoo, Kristina, Anil Chuturgoon, Geremy Cliff, Sanil Singh, Megan Ellis, Nicholas Otway, Andre Vosloo, and Michael Gregory. “Possible Maternal Offloading of Metals in the Plasma, Uterine and Capsule Fluid of Pregnant Ragged-Tooth Sharks (Carcharias taurus) on the East Coast of South Africa.” Environmental Science and Pollution Research 24, no. 20 (July 1, 2017): 16798–805. https://doi.org/10.1007/s11356-017-9281-1.

Sota, Teiji. “Altitudinal Variation in Life Cycles of Carabid Beetles: Life-Cycle Strategy and Colonization in Alpine Zones.” Arctic and Alpine Research 28, no. 4 (November 1, 1996): 441–47. https://doi.org/10.1080/00040851.1996.12003197.

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Sure, insects in particular are incredibly diverse and while some have multi-stage life cycles which can extend over years, others reproduce multiple times a year.

Common/popular examples of the former are the periodic species of cicada that take 13 or 17 years to emerge as adults, or the woolly bear, which remains as a caterpillar for possibly several seasons, depending on the time it takes to grow, before becoming an adult. If you're looking for exactly a 2-year cycle, a woolly bear in the right conditions would qualify.

Another example is the spruce beetle; like the woolly bear, growth time depends on conditions, but the two-year cycle is most common.

There are so many species of insects that it's likely examples could go on and on and fill books.

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Albatrosses have biennial breeding and sabbatical years where they can travel 120,000 km on their 4m wings: https://www.nature.com/articles/srep08853

There are very many species of arthropods which stay in a grub stage 2,3, 4 up to 17 years. Seven species of North American periodic cicadas swarm every 13 or 17 years locally at the same time. https://en.wikipedia.org/wiki/Periodical_cicadas?wprov=sfla1

https://entnemdept.ufl.edu/walker/ufbir/chapters/chapter_12.shtml

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