July Insect Phenology

by Carl Strang

First observation dates for insect species at Mayslake Forest Preserve in July 2011 were not too different from 2009 and 2010. The median difference in dates placed 2011 ahead of 2009 by 3 days (range 17 days earlier to 16 later, sample of 13 species). This year’s July appearances were a median 7 days later than in 2010 (range 30 days earlier to 80 days later, sample size 15 species).

The red milkweed beetle was representative of these results, with a first observation date in 2011 that was 3 days earlier than in 2009, 6 days later than in 2010.

Dropping the 80-day-later outlier, which probably represents my missing a generation earlier in the season, shifts the median difference between 2010 and 2011 to 5.5 days later, not a very big change.

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