Mass movement of Kricogonia lyside

[Kenn Kaufman]

One of the pierids that regularly invades northward 
into Arizona in summer, especially in years when the 
rains have been good in Sonora, is Kricogonia lyside
(Lyside Sulphur).  These invasions often take the form 
of simultaneous mass migrations.  Today (25 July 
2001), such a mass flight was passing through the 
northern foothills of Tucson.  

At a point about half a mile south of Sabino Canyon 
visitor center, I first noticed numbers of K. lyside 
flying past about 11:00 a.m. MST.   Individuals were
passing at an estimated rate of 10 - 20 per minute.  
Abandoning the work I should have been doing, I 
went out to make some serious counts.  Numbers 
increased rapidly, and during the period from about 
11:20 to 11:50,  50 to 100-plus per minute passed 
across a stretch of hillside about 30 yards wide. 
Virtually all individuals were flying toward the 
northeast or east-northeast, a minority stopping 
briefly at nectar (Lantana, Ageratum, etc.).  Most 
that I counted were within 20 or 30 feet of the 
ground, but occasional scans with binoculars 
showed that others were going over much higher, 
perhaps 100 feet or more, traveling in the same 
direction.  Numbers gradually tapered off after 
12:00 but they were still passing at 10 - 20 per 
minute at 12:30, 1:30, and 2:30 when I checked 
again.  During the peak passage I netted a few 
dozen for examination and all were in fairly fresh 
condition or only slightly worn.  

Checking with a couple of other naturalists by 
phone, I learned that Carl Englander was seeing 
similar numbers at a point five miles west and 
one mile north of where I was (but his were 
flying north or even north-northwest), while Rick 
Bowers watched for an extended period at a 
point twelve miles west of me and saw none 
at all.  Bowers's position was in the flats at 
some distance away from the mountains, while 
Englander and I were at the immediate edge of 
the Santa Catalina Mountains; the concentrations 
that we saw, as well as the difference in flight 
directions, could have been explained if the 
sulphurs had all come in from the south at a 
fairly high level but were detouring to go around 
the mountains rather than over them.  

A little past the peak of the flight, when I stood 
on a low ridge and looked toward a distant slope, 
the foreshortened effect through binoculars made 
it look like a blizzard of creamy-white butterflies 
was blowing past.  Pretty amazing spectacle. 
Certainly tens of thousands of K. lyside were 
passing over Tucson today.  Anyone doing 
fieldwork to the north of here during the next 
couple of weeks should keep an eye out for 
this species.  

Kenn Kaufman
Tucson, AZ
kennk at ix.netcom.com



 
 ------------------------------------------------------------ 

   For subscription and related information about LEPS-L visit:

   http://www.peabody.yale.edu/other/lepsl