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 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 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 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 at 10:18
  • $\begingroup$ 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 at 1:53

2 Answers 2


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.


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



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