Why the butterflies were fighting

Please note: News about my book can now be found on
http://www.cpind.blogspot.com

Rosemarie Bria has sent in an explanation for why the sulphur butterflies in yesterday's post were attacking a Yellow Swallowtail on a flower. To read the entire article, here's a link:
http://www.public.iastate.edu/~mariposa/contests.htm

Butterfly Territorial Contest Dynamics

People are often surprised to learn that some butterflies are territorial. This may be due to the common view of butterflies as being carefree, fluttery creatures. Yet some male butterflies, including some in the genus Vanessa, are capable of maintaining and aggressively defending territories through purposive behaviors such as patrolling flights and complex interactions in flight with intruders of their own species (Bitzer and Shaw 1979).

One reason that territorial behavior was slow to be recognized and studied in insects was that physical aggression in defense of resources is often less overt than it is for birds and mammals (Baker, 1983). Butterflies especially might seem at first thought to have little capacity for physical aggression. Thus Scott (1974) and Suzuki (1976) insisted that what seemed to be a perching male butterfly's "defense" of an area could alternatively be interpreted as the male's merely investigating passers-by to determine their species and sex. Intruders' so-called "evasive" response could likewise be interpreted as an attempt to avoid a possible predator (Scott, 1974). Scott (1974) also proposed three criteria that a butterfly's perching behavior would need to meet before the behavior could be considered truly "territorial." These were: 1) many males must remain at the same spot for several days, 2) males must be able to quickly distinguish males from females, and 3) males must "by intent" drive other males from the area.