Blue-eyed grass

Field Trip Report: Lincoln Trail State Park
July 15, 2007

The weather and the bugs were great on our field trip to Lincoln Trail.  The highlights were a juniper hairstreak (20 feet up in a red cedar, but nice nonetheless!) and some nice looks at lots of dragonflies.

 Our butterfly species list (18 species) for the day was: pipevine swallowtail, black swallowtail, spicebush swallowtail, tiger swallowtail, cabbage white, orange sulphur, clouded sulphur, eastern tailed-blue, juniper hairstreak, pearl crescent, question mark, red admiral, great spangled fritillary*, American snout, common buckeye, monarch, silver-spotted skipper, and least skipper. [* = seen on the way to Lincoln Trail]

Our dragonfly/damselfly species list for the day was: prince baskettail, Eastern amberwing, Eastern pondhawk, blue dasher, slaty skimmer, common whitetail, widow skimmer, eastern forktail, blue-fronted dancer.


*If anyone wants to provide more complete information or corrections for any of the below items, feel free to contact the club by email*

All photos copyright Paul V. Switzer. Please do not use without permission




Question mark
This question mark was puddling on something that had spilled in the parking lot where we met for the beginning of our trip.

Eastern amberwing
In past field trip reports, there have been photos of amberwings in a thermoregulatory posture known as an "obelisk", with their abdomens pointing towards the sun to minimize the surface area that is absorbing heat.  This male is showing a different thermoregulatory posture:  he is holding his wings at angles to help shade his body and pointing his abdomen down (away from the sun) to minimize heat gain.

Orange sulphur
Eastern tailed-blue

Prince baskettail
These large dragonflies typically forage high over fields during the day and visit ponds and lakes in the evening to breed.  The name "baskettail" describes its genus (Epitheca) within the dragonfly family of Corduelidae.  Female baskettails hold their eggs in a clump at the tip of their abdomens when looking for places to lay them.  In this view you can also see where the Corduelidae get their common name "emeralds": note the green eyes!
  Slaty skimmer
The slaty skimmer's bluish-black coloration also comes from a pruinescent covering.

Prince baskettail

Eastern pondhawk
(immature male)
This male will gain a light-blue, powdery/waxy coating called pruinescence when it matures.

Blue-fronted dancer
This photo is very similar to a picture taken of the same damselfly species last year at Lincoln Trail - but it must be a different individual, because damselflies in our region would have at most a one year life cycle (nymph to adult), with adults typically only living a few weeks.

Prince baskettail
Insect eyes are compound, which means that instead of one lens, they have many, with each facet (ommatidium) of their eye containing its own lens and photoreceptors.  These multiple images are integrated into one combined image in their brain, just as the images from our two eyes are combined into one image (the "kaleidoscope" image of insect vision that is often shown in B-movies is not correct!).

The smaller the facets, the higher the resolution of the eye, just as the smaller the tiles in a mosaic (or the higher the density of pixels in a digital photo), the clearer the picture.   Insects with lots of tiny ommatidia are often either predators (such as this dragonfly) or active, visual mate-seekers (such as males of some true flies or bees).  Compound eyes and their associated neural machinery usually have high flicker fusion rates, which means that they can resolve rapidly changing images as separate images instead of as a blur (e.g. they would see the a typical fluorescent light as a strobe, whereas we see continous light).  This high flicker fusion rate is a useful adaptation for flight, allowing them to see clearly the landscape as it passes.  So, a dragonfly such as this baskettail can see rapidly changing images clearly, and it can resolve small, moving objects clearly.  This helps them fly fast and catch small, quickly-flying insect prey.  


Orange sulphur
Continuing our "eye" theme, here is a close-up of a male orange sulphur. 


Eastern amberwing
The black, oval dot you see in this male's compound eye is called a "pseudopupil", which represents the ommatidia that are most directly lined up with the direction of the viewer.   Because of this, the pseudopupil will seem to move in the eye as you change your perspective relative to the insect.

Another cool thing about compound eyes is that different parts of the eye can be specialized for different types of vision. You can see that in this amberwing eye; the top, dark-brown part has different properties and abilities than the lighter-colored, bottom part. [I also like the fact that this male seems to be smiling for the photo!]

Milkweed longhorn beetle
Monarch caterpillar

Pipevine swallowtail
The pipevine swallowtail is the poisonous black butterfly that the other large black butterflies reportedly mimic (i.e. the black swallowtail, spicebush swallowtail, black morph of the female tiger swallowtail, and red-spotted purple).  The pipevine can be distinguished from the swallowtail mimics by its single row of large orange spots and irridescent greenish-blue cast.
Pipevine swallowtail
In contrast to the blue on the mimics (e.g. see the spicebush below), the blue on the pipevine is dependent on the angle of the light (compare the photo above to the one at left).  That makes a flying pipevine swallowtail often look flat-black as it flies, with occasional flashes of irridescence.

Spicebush swallowtail
The spicebush swallowtail has two rows of orange spots but is missing one spot on the inner row (see the blue "comet" in the third spot up from the bottom) and its blue color doesn't depend on the direction of the light. [FYI, the black swallowtail female looks very similar to the spicebush, but isn't missing the spot in the inner row.]
Mushroom (Amanita parcivolvata)
I think this is the first fungus to grace the a GPBC field trip report; it was just too neat to pass up.  Thanks to Michael Kuo (of EIU and mushroomexpert.com fame) for the identification!


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