May Phenology: Flowers and Insects

by Carl Strang

Probably the best phenological comparisons between years involve plants. That is because plants respond to soil conditions, which average the weather for the year to date. Also, there are many species of plants, increasing the number of comparisons that can be made and reducing the chance for error. I focus mainly on first flower dates. This year I was able to compare 41 species to 2010, and 44 species to 2009. The continued cool spring has made this the latest of the 3 years for first flower dates in May. The median values for 2011 were a whopping 14 days later than in 2010, and 4 days later than 2009, which also was a remarkably late year.

The wild hyacinth did not closely match the overall pattern, blooming 7 days later than in 2010 and 6 days earlier than in 2009.

The final set of phenology data I record are first observations of insect species. Here the results are shakier, in part because the number of species is small for May, at around 10, and in part because of the possibility of missing representatives of the year’s first generation of a species.

I saw the first tiger swallowtail at Mayslake Forest Preserve 16 days earlier than in 2010, 8 days earlier than in 2009.

The median dates for 2011 were 7 days earlier than in 2010, and 12 days earlier than in 2009. However, if I leave out species with more than one generation in which I obviously missed the first in the earlier years, medians shift to 9 days later than in 2010, 5 days later than in 2009.

The four-spotted skimmer shows how wildly erratic the insect data can be. My first observation for 2011 was 9 days later than in 2010, but 61 days earlier than in 2009.

Adjusting the data in that way is sensible, and produces a result consistent with what we see in the plants.

Mayslake Lepidoptera Update

by Carl Strang

As we move into autumn, the lateness of the season calls for us to enjoy the more ephemeral beauties of nature while we still have them. Monarch butterflies have completed their local mating and egg-laying, and have begun the migration south toward Mexico.

Monarchs mating b

Earlier in the season at Mayslake Forest Preserve I found this larva of the moth Cycnia tenera on its usual food plant, dogbane.

Cycnia tenera b

Tiger swallowtails are one of our more spectacular butterflies.

Tiger swallowtail 1b

They will overwinter in the pupal form. Late season species include the summer azure.

Summer azure b

Larvae of this little butterfly feed on flowers in the composite (sunflower) family; I have seen them laying eggs on wingstem at Fullersburg . Another common late summer species is Peck’s skipper.

Peck's skipper b

There probably will be little more to report on this group at Mayslake until next year.

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