May Insect Phenology

by Carl Strang

As was the case with flowering phenology, insect species that first appeared in May did so earlier than in recent years at Mayslake Forest Preserve. The median difference between this year and last was 14.5 days earlier for 18 species, with a range of 86 days earlier to 5 days later. The median difference between 2012 and 2011 was less, at 8 days earlier for 15 species, ranging 21 days earlier to 46 days later. The difference was larger again with respect to 2009, a median of 16.5 days earlier for 14 species, ranging 95 days earlier to 46 days later.

Many of the early species were dragonflies, possibly finishing their development more quickly as waters warmed early this year. The first blue dasher appeared 9 days earlier than last year, 21 days earlier than in 2010, and 14 days earlier than in 2009.

With soil warming and plants growing so much more quickly, it is no surprise that plant-eating insects also were represented among the early species.

I saw the first least skipper on May 22 this year, June 8 last year, June 10 in 2010 and June 2 in 2009.

A third category was migrants, with the monarch butterfly being the iconic species here.

The first monarch arrived on May 4 this year, May 11 last year, May 19 in 2010 and May 26 in 2009.

Though local conditions would not have brought migrants here sooner, much of the U.S. had an early spring which could translate into quicker development of the offspring of those monarch migrants that overwintered in Mexico.

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