More Insects Emerge

by Carl Strang

Phenology, the timing of natural history events, is an easy area of study that adults or schoolchildren can pursue. I have been sharing my phenology observations at Mayslake Forest Preserve for first flowers, first fruits, and spring arrivals of migrant birds. Today I would like to look at results comparing 2009 and 2010 spring first sighting dates of insects. Insects are small and easy to overlook. Their numbers can vary a lot between years. Consequently I am not going to place too much weight on small differences between years for individual species. A case in point is the hobomok skipper.

I have seen few of these at Mayslake. Nevertheless, last year’s first date of 5 June is very close to this year’s June 9. Similarly, the first prince baskettail dragonfly appeared on June 1 last year, June 10 this year.

They seldom land, so I’m resorting to a UFO photo here. The difference in dates for Peck’s skipper is large enough to suggest a brood difference. I saw this one on May 25 this year.

The first date last year was August 24. This represents last year’s second generation, and I did not see a first generation representative. I don’t see many of these butterflies, so this is not a surprising result. I also haven’t seen many lyre-tipped spreadwings

Thus I am not willing to put much emphasis on the between year difference in first sightings of 13 July 2009 vs. 10 June 2010 for this damselfly.

So much for individual species. I was interested in looking for patterns among seasonal groups of species. In March this year I had only 2 species to compare to 2009, with a median difference of 5 days earlier than last year. April numbers were 9 species, median 17 days earlier than 2009. The 12 May species had a similar 16.5 days earlier median. To date in June, 9 species are a median 4 days earlier. These results suggest that the warmer spring this year is producing emergence patterns in insects that are similar both in direction and amount to those of first flower dates in plants.

Mayslake Lepidoptera Update

by Carl Strang

Recently I provided an update on damselflies and dragonflies that have become active at Mayslake Forest Preserve. New butterflies and moths also have been appearing. The large group of butterflies known as skippers can be tricky, but I believe I have these right: Hobomok skipper,

Hobomok skipper b

and tawny-edged skipper.

Tawny-edged skipper 2b

Both are, according to my references, common. I have found Hobomoks in other preserves early in the season. Even more common and distinctive are two more species, the least skipper

Least skipper 2b

and silver-spotted skipper, the latter never far from black locust trees.

Silver-spotted skipper b

The most recent butterfly to show itself has been the spring azure.

Spring azure 2b

Moths also are in evidence. This one, Zanclognatha cruralis, belongs to a curious group whose larvae eat dead leaves.

Zanclognatha cruralis b

The following moth I photographed on the slope between May’s Lake and the friary, not far from a large white pine.

Semiothisa bisignata cropped b

This one proved to be a tough ID. There is a large group of moth species which look very much like this one. Furthermore, many of these species show considerable variation among individuals. The yellow head and anterior thorax are unusual among them, I gather, and help to narrow down the possibilities. My tentative identification is Semiothisa bisignata, the caterpillars of which eat pine needles. In the future I may need to collect one or more of them. With some insects, photographs simply aren’t enough.

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