Category Archives: Insects

Jewelweed

The last hummingbirds of the season are feeding in the jewelweed patch behind Stirling’s Coffee House.

Jewelweed flowers offer nectar to the hummingbirds from a nectar spur at the end of a cone-shaped flower. The hummingbirds have to insert their beaks all the way in to reach the nectar and in doing so they receive a dab of pollen on their foreheads. Many of the hummingbirds in the patch have heads that are completely coated in pollen.

Jewelweed, Impatiens capensis, with nectar spur visible on the far right

The last thing a hummingbird sees before it sinks its beak into the flower. The pollen dusters are at the top of the flower.

Not all spurs are the same shape. Some are curled, others are straight. It turns out the the more curvy spurs result in better pollen transfer to the hummingbirds, probably because the birds have to reach down further to get the nectar.

Compare this piglet-tailed spur to the one above.

The degree of curvature is heritable, so this is a feature that can evolve through natural selection. Why, then, don’t all flowers have the same degree of curl? No-one knows, but the diversity of pollinators that visit jewelweed may favor a diverse set of nectar spur designs.

Bumblebee visiting the same jewelweed patch.

Jewelweed is also called-touch-me-not: a gentle pinch to the bottom of the seed capsule will cause the seeds to explode outwards, shooting several feet away. Gram for gram, the energy stored in these seed pods exceeds that of steel in springs.

Waiting to explode...

As an extra bonus today, the jewelweed patch also hosted a beautiful red phase screech owl. The scolding wrens gave away its location in the shrubs.

Dick Cove

My Field Investigations in Biology class ventured into the old growth forest in Dick Cove (aka Thumping Dick Hollow, apparently named for a former inhabitant who built an ingenious corn-pounding device). In addition to measuring trees to quantify how the forest community is changing, we found some interesting creatures in the undergrowth.

First question, thanks to Ruffin: can you spot the animal?

Camouflage on leaves

How about now, when it sits on a rock?

Spring peeper, Pseudacris crucifer. The scientific name derives from the cross on the animal's back.

Another cryptic creature, this time an unknown Hemipteran bug:

...and Mary demonstrates how to "picture-bomb."

Allie found an archaeological artifact (or, trash, depending on your perspective). After some debate, we left it in place. The mini-terrarium inside was remarkable — soil had accumulated over the years, then moss spores somehow found their way in.

Bryophytes in a bottle

Another world inside; like the Sewanee Bubble.

Last, Jeff found a spectacular Philomycus under some bark of a downed log. These native gastropods are “mantleslugs” and they are as big as cigars.

Philomycus with the fecal remains of its fungus dinner.

Waterscorpion

My Field Investigations in Biology class ignored the rain and had a great time scooping various animals from Lake Cheston. The finest catch was this waterscorpion. The insect was as long as my index finger. Waterscorpions are fierce predators and will eat both insects and small vertebrates. They pierce the victim with their sharp mouthparts, then suck it dry.

Waterscorpion (Genus Ranatra, Family Nepidae) impaling a dragonfly nymph. The long thread-like attachments on the tail are breathing tubes that the waterscorpion raises above the water surface when it needs oxygen.

Goldenrod pollen

Goldenrods (Solidago sp.) are in full bloom, giving insects a welcome bonanza of pollen.

A bumblebee packs pollen into "baskets" on its hind legs. The baskets are made from long hairs.

Paper wasps (genus Polistes) also love the flowers. Some studies of goldenrod ecology suggest that these wasps may be the main pollinators of goldenrod. These wasps are normally very flighty, but on goldenrod they seem to settle down to the serious business of investigating every floret on the flower stalk.

Lesser angle-wing katydids

They start singing about an hour after dark, calling with short bursts of high-pitched sound. Each call is somewhat like a can of dried peas being shaken rapidly. In the following recording, the lesser-angle wings call five times. You’ll also hear the common true katydid singing “di-di-did” in the background. Crickets are also singing in this clip — they form a continuous band of sound against which the katydids play.

Lesser angle-wing katydid, Microcentrum retinerve. This individual flew into the kitchen and posed briefly on the wall.

For comprehensive identification information on America’s many katydids (including sound files) see Walker and Moore’s excellent online guide.

Bumblebee studies Fibonacci series

The number of spirals of florets in the center of the sunflower always follow the Fibonacci series. This is apparently the result of the angle between adjacent florets, which is about 137 degrees, or the "golden angle", giving the most efficient packing of florets into the head. Bees like golden, especially in the form of pollen.

Plenty of material to study.

Visual confirmation of the waaa-oo cicada

…also known as Magicicada tredecim. I’ve been hearing them for weeks, but this is the first one I have managed to catch and examine closely. Regrettably, all the thirteen year cicadas seem to be fading away now. So long, until 2024…

Magicicada tredecim. Underside of abdomen is mostly orange. Compared to Magicicada tredecassini, which is often found at ground level, this species seems to prefer the treetops.

Getting ready for the year 2024

This female cicada was laying eggs today on the spicebush outside our house. She makes a small slit in the stem, then deposits eggs in the opening. The eggs remain on the twig for a few weeks, then the nymphs hatch out and fall to the ground. Here, they burrow down into the soil and live for thirteen years, feeding on tree roots. The Class of ’24 is underway.

Magicicada tredecassini depositing eggs from the tip of her abdomen

And, for some remarkable timelapse photography of an emerging cicada, see Mark Dolejs’ Vimeo post.

Which species of periodical cicada do we have here?

According to the magicicada.org website, three species are possible in Sewanee:

Magicicada tredecim — Underside of abdomen is mostly light orange/caramel. These are the ones that call waaa-oo from the treetops.

Magicicada tredecassini — Underside of abdomen usually all black, or with faint orange lines.

Magicicada tredecula — Well-defined orange stripes across underside of abdomen.

This individual crashed into my head while I was watering the garden, so I brought him down with the water jet and did some catch-and-release identification: Magicicada tredecassini. The sound he was making seems to match that on the magicicada pages also.