The hydra effect or hydra paradox owes its name to the Greek legend of the Lernaean Hydra which grew two heads for each one cut off, and is used figuratively for counter-intuitive effects of actions to reduce a problem which result in stimulating its multiplication. Most notably scientists have proposed that ecological systems can exhibit a hydra effect when "a higher death rate in a particular species ultimately increases the size of its population". The hypothesis is suggested to have implications for the eradication of pests, and resource management. There are also said to be indications that reducing the death rate can shrink a population.
The hydra effect has also been used about negative outcomes when shutting down torrent sites which come back in more incarnations, and is cited by those opposing the war on drugs and targeted killing as counter-productive effects. In 2016 the site Torrentz shut down its operations without further information for the cause of the shut down. However, within two weeks, there were 3 torrent sites that were built as replacements for Torrentz, which stands as a perfect example of the hydra effect. Similarly, after the torrent website The Pirate Bay was shut down in December 2014, it reincarnated with hundreds of copies within a week.
- Abrams, Peter (27 May 2015). "Hydra paradox: When culling animals makes them thrive". New Scientist.
- Clark, Liat. "Shutting down huge pirate sites has no 'positive effect'". Wired UK. Retrieved 26 June 2015.
- Blum, Gabriella and Philip Heymann (June 2010). "Law and Policy of Targeted Killing" (PDF). Harvard National Security Journal. 1: 165. Archived from the original (PDF) on 7 September 2012. Retrieved 11 February 2013.
- Elias Garcia (4 September 2014). "The Hydra Effect and the War on Drugs". Archived from the original on 24 May 2015. Retrieved 23 May 2015.
- Van der Sar, Ernesto. "Torrentz Remains Down, But The Clone Wars Are On". TorrentFreak.
- Ernesto (27 December 2014). "Hundreds of Pirate Bay Copies Emerge, Is The Hydra Alive?". Retrieved 23 May 2015.