Editing Swarm behaviour (section)

====Migratory behavior====
[[File:Monarch flock.jpg|thumb|upright|Cluster of [[Monarch butterfly|monarch butterflies]]. Monarch butterflies migrate to [[Santa Cruz, California]], where they [[overwinter]]]]
{{Main|Insect migration}}
{{See also|Lepidoptera migration}}
[[Insect migration]] is the seasonal movement of [[insect]]s, particularly those by species of [[dragonfly|dragonflies]], [[beetle]]s, [[butterfly|butterflies]], and [[moth]]s. The distance can vary from species to species, but in most cases these movements involve large numbers of individuals. In some cases the individuals that migrate in one direction may not return and the next generation may instead migrate in the opposite direction. This is a significant difference from [[bird migration]].

[[Monarch butterfly|Monarch butterflies]] are especially noted for their lengthy annual migration. In North America they make massive southward migrations starting in August until the first frost. A northward migration takes place in the spring. The monarch is the only butterfly that migrates both north and south as the birds do on a regular basis. But no single individual makes the entire round trip. Female monarchs deposit eggs for the next generation during these migrations.<ref>Pyle, Robert Michael, "National Audubon Society Field Guide to North American Butterflies", p712-713, Alfred A. Knopf, New York, {{ISBN|0-394-51914-0}}</ref> The length of these journeys exceeds the normal lifespan of most monarchs, which is less than two months for butterflies born in early summer. The last generation of the summer enters into a non-reproductive phase known as [[diapause]] and may live seven months or more.<ref name="ref1">{{cite web |url=http://www.dbc.uci.edu/~pjbryant/biodiv/lepidopt/danaidae/monarchm.htm |title=Monarch, Danaus plexippus |access-date=2008-08-27 |url-status=dead |archive-url=https://archive.today/20121215095741/http://www.dbc.uci.edu/~pjbryant/biodiv/lepidopt/danaidae/monarchm.htm |archive-date=2012-12-15}}</ref> During diapause, butterflies fly to one of many overwintering sites. The generation that overwinters generally does not reproduce until it leaves the overwintering site sometime in February and March. It is the second, third and fourth generations that return to their northern locations in the United States and Canada in the spring. How the species manages to return to the same overwintering spots over a gap of several generations is still a subject of research; the flight patterns appear to be inherited, based on a combination of the position of the sun in the sky<ref>Gugliotta, Guy (2003): [http://ipm.osu.edu/trans/053_231.htm Butterflies Guided By Body Clocks, Sun Scientists Shine Light on Monarchs' Pilgrimage] {{webarchive|url=https://web.archive.org/web/20060305034410/http://ipm.osu.edu/trans/053_231.htm |date=2006-03-05}}. ''[[Washington Post]]'', May 23, 2003, page A03. Retrieved 2006-JAN-07.</ref> and a time-compensated Sun compass that depends upon a [[circadian clock]] that is based in their antennae.<ref>{{cite journal |vauthors=Merlin C, Gegear RJ, Reppert SM |year= 2009 |title= Antennal Circadian Clocks Coordinate Sun Compass Orientation in Migratory Monarch Butterflies |journal= Science |volume= 325 |issue= 5948 |pages= 1700–1704 |doi= 10.1126/science.1176221 |pmid= 19779201 |pmc= 2754321 |bibcode= 2009Sci...325.1700M}}</ref><ref>{{cite journal |author= Kyriacou CP |year= 2009 |title= Unraveling Traveling |journal= Science |volume= 325 |issue= 5948 |pages= 1629–1630 |doi= 10.1126/science.1178935 |pmid= 19779177|s2cid= 206522416 }}</ref>