Jane, what you are probably seeing is the result of chilled brood.
This occurs often in the spring when the brood nest has expanded,
a sudden cold snap occurs, and the bees are unable to maintain the
temperture over the complete brood area.  They collapse into a
smaller area over the cold period and then the exposed brood die.
After the cold snap, the bees clean out the dead brood and begin
again.  You must have been hit by the blizzard of '92 that just
swept the whole eastern part of the United States and Canada.  I
would also guess that you are further south than my location on
Long Island.  We still have limited brood rearing.
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+    Raymond J. Lackey                                     +
+    Beekeeper 10 years with 25 colonies on Long Island    +
+    INTERNET: [log in to unmask]                 +
+    Mail: 1260 Walnut Avenue, Bohemia NY 11617            +
+    Home Phone: 516-567-1936  FAX: 516-262-8053           +
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