Insect First Appearances in April

by Carl Strang

In the previous post I shared data from Mayslake Forest Preserve showing that plants are continuing to bloom 2-4 weeks earlier than in the previous 3 years. Insects that made their first appearances in April likewise were ahead of 2009-2011.

The eastern forktail was representative, appearing 35 days earlier than in 2009, 41 days earlier than in 2010, and 34 days earlier than last year.

Sample sizes were small, though, with only 7 species to compare between each pair of years. The median difference between 2012 and 2009 was 43 days earlier (range 169 days earlier to 25 days later). The median was 41 days earlier than in 2010 (range 110 days earlier to 24 days later), and 35 days earlier than in 2011 (range 27 to 68 days earlier).

The first pearl crescent appeared on April 9 this year. That date was September 23 in 2009, July 2 in 2010 and May 12 last year.

These huge ranges may better be described as representing better survival for many species in the mild winter just past, so that there were more first-generation individuals, increasing the likelihood that I would see one. The pearl crescent could well be a case in point with respect to 2009 and 2010.


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