Phoebis sennae/ Cloudless Sulfur

[Chip Taylor]

Relatively large numbers (10's of thousands) of the Coludless sulfur,
Phoebis sennae, have been moving through eastern Kansas (Lawrence and
vicinity) and western Missouri (KCI) since at least the 20th of August.
Directional flight usually occurs from 9AM until 4-5PM if the skies are
clear or cloud cover is less than 50%. The headings are generally 120-140
degrees. These butterflies are probably offspring of adults which moved
into KS from the SE in July. The local host is Partridge Pea which grows in
dense patches in roadside ditches, wet margins of fields and wetlands. A
few of the females are laying eggs on a Cassia I've placed in my milkweed
garden. Unlike fall migrating monarchs which are generally in reproductive
diapause, sennae remains reproductive during it's migrations. Although this
is a well known migratory species, it's migratory behavior is still not
well understood. Observations of headings and conditions during migratory
flight are needed for many areas of the country.  For further information
on how to study this and other migratory insects the curious/interested
might consult the excellent web site created by David Gibo of the
University of Toronto - http://www.erin.utoronto.ca/~w3gibo. Information on
how to observe and record vanishing bearings and body headings can also be
found at http://www.monarchwatch.org
Where this species is abundant, it could be used to introduce students to
migratory behavior and the enigmas of orientation and navigation. The
directions taken by sennae from Aug through the first week of Nov., in the
midwest at least, are always east of south while those of the monarch range
from 180 to 280 depending on latitude and longitude. In September, in
Lawrence, the monarchs have mean headings of 210-220 while the sennae
usually have headings that range from 120-160. This may be an excellent
year to obtain data on the flight directions of sennae and monarchs in
several areas of the country at the same time.


Monarch Watch
Email:  monarch at ukans.edu
WWW:  http://www.MonarchWatch.org/
Dplex-L:  send message "info Dplex-L" to Listproc at ukans.edu
Phone:  1 (888) TAGGING (toll-free!) -or- 1 (785) 864 4441
Fax:  1 (785) 864 4441 -or- 1 (785) 864 5321
Snail:  c/o O.R. Taylor, Dept. of Entomology, Univ. of KS, Lawrence KS 66045