Natural Events

Here’s what’s debuting on nature’s stage in Chicago Wilderness

By Jack MacRae

Early Summer

In The Navy

Red admirals dress sharp. The uniform of these common backyard butterflies features prominent vermilion bands across their forewing and along the margin of their hindwing. A few white dots at the apex of the wing add panache. During summer, the female admiral will place small, green, barrel-shaped eggs on the topsides of wood nettle, a common local host plant.

It’s not difficult to locate the red admiral; they’ll often fly close to people. Males seem to patrol an oval-shaped territory, and quickly cruise over to investigate any intruder.

Light Fantastic

Fireflies, the delightful insects that create those trippy summer light shows, are beetles, not flies. The show starts in June, when male fireflies use bioluminescence to send coded signals to attract prospective mates, who respond with the same signal. Each species of firefly has its own unique male signal and female response. When the airborne male spies an appropriate response from the stationary female, he lands and they mate.

The “fire” is a “cold light” that contains virtually no ultraviolet or infrared bands of the spectrum. The yellow, abdominal glow is the byproduct of a reaction between oxygen, the chemical luciferin, and an enzyme that catalyzes the reaction.

Middle Summer

Old Soft Shell

Spiny softshell turtles live large in Chicago Wilderness. Last summer I saw a big, old female that might have been 18 inches long. She leads a simple life, spending summer lounging in the sun and generally going with the flow in our slow rivers. During June, she’ll lay her eggs, 18 on average, in a gravelly nest. Her parental duties are then over and she can get back to serious basking, soaking up the full spectrum of the sun’s rays. She has a cute little face, but don’t pick her up. Under her fleshy lips is a hard bony mouth, and she can deliver a nasty bite.

Turkey Days

Turkey vultures are a common sight in our wild summer skies. Long, ragged-tipped wings held slightly dihedral (in a slight V) are the identifying traits of these large aerial scavengers.

Nature has provided the vulture with a body well-equipped for peeing on itself. The bird’s urinary tract drains immediately onto its legs, allowing urine and feces to flow directly onto the vulture’s featherless skin. Scientists call this practice urohydrosis and believe it may be used in regulating body temperature. Urine cools the legs as it evaporates. In addition, the powerful antibacterial properties of the uric acid may act as a sterilizing agent, protecting the vulture from toxins it picks up while wading through a meal of rancid meat.

Late Summer

Purple Campers

Camp Purple Martin takes place in August, in the public parks along the edge of Lake Michigan. This annual gathering brings many thousands of these swift flyers together as they make final preparations for their trip to the Southern Hemisphere. Purple martins appear at their Chicago Wilderness roosting areas at dusk, arriving in flocks of hundreds from points north and west.

Traditionally, they’ve used various spots in Lincoln Park and Montrose Park for their branch camp; but the trees next to the Ape House at Lincoln Park Zoo have been popular in recent years. Purple martins are the largest of the swallows, which, some might say, makes them gulps.

Good Grass

Aptly named, porcupine grass produces incredibly hard, sharply pointed seeds toward the end of summer. The seed is attached to a long, slender “awn.” At the end of the growing season, porcupine grass will lean over and drop its awns with their seeds. As they dry out, each awn will twist into an elegant, symmetrical corkscrew. Moisture can cause the awns to straighten again. Some ecologists think that this twisting and untwisting allows the awns to snake their way through vegetation and drill the seeds efficiently into the soil. Check it out at a dry prairie near you.