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.

The American Snout, and More

by Carl Strang

One of my favorite animal names is “American snout.” It calls forth the image of some disembodied nose floating in space. In fact it’s a reference to a butterfly with a long forward extension of its head.

This butterfly was the first of its kind I have observed at Mayslake Forest Preserve. It is more common south of us. In references you may find its species name as carinenta or bachmanii; the genus is Libytheana, and there is only one North American species.

Another preserve first was this brightly colored beetle.

The milkweed leaf beetle, like so many consumers of milkweed, has bright orange colors. These warn potential predators of the possibility of poisons the insect may have sequestered from its diet.

I saw a couple bluets that had the relatively large size and the color pattern of familiar bluets.

The males had this violet coloration, though; my guess is that they had recently emerged as adults and would be changing colors soon.

I have been seeing more Virginia ctenucha moths than usual this year, at Mayslake and elsewhere.

That’s the way it is with some insects, having occasional years with higher numbers.

Of course, a major goal of all these adult insects is to find a mate and produce eggs.

For this pair of least skippers, it’s so far, so good.

On Friday I finally saw the first Peck’s skipper of the year.

The pattern of light spots beneath the hindwing is distinctive for this species.

It’s been a good year for insects, so far.

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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