Variety’s the very spice of life…

I ran across this quote while doing a crossword…

Quote from William Cowper, from his multi-volume poetic work, The Task.

It is variety indeed that makes us marvel at natural wonders.  Something simple, like variation in the colors of Black-eyed Susan flowers.  Who knew there were 43 varieties of Black-eyed Susan, ranging in color from yellow to bright fuchsia to dark mahogany, with all manner of stripes and blotches on the petals.

A mixed bag of wildflower seed yielded the following results in my garden:

Not different species of wildflowers, but different varieties of one species, Rudbeckia hirta.

Close-up, they are quite striking.

The more standard version of Black-eyed Susan that we usually see.

Variety just makes life more interesting.

A fly to love…

HMost flies seem kind of ugly to me, or perhaps it’s just their behavior I dislike —  buzzing around my head and occasionally biting.  But here is a fly to admire, and in fact to cultivate in your garden.

A easily recognized fly, with its white scoop face, stubby antennae, red eyes, and bristly black butt.

An easily recognized fly, Archytas apicifer, performs a valuable service by pollinating the flowers of many plant species.

Not exactly beautiful, but striking in its features, with its white face, red eyes, and bristly black butt.  Archytas apicifer doesn’t seem to have a common name, but I’ll refer to it as White-faced Fly here.  It is a member of the Tachinidae family, a very large group (~10,000 species), all of whom are parasites on other organisms.  White-faced fly happens to be one of the larger species, about 1 inch in length, and a very fast and agile flyer.  The adults are fond of nectar and may be good pollinators.  I found them in great numbers on the Black-eyed Susans and Canada Goldenrod in my backyard.

On the Black-eyed Susans, the fly systematically explored every open disc flower by circling the flower head.

On the Black-eyed Susans, the fly systematically explored every open disc flower by slowly circling the flower head.  Its antennae project downward over a scooped out portion of the “face”, which makes me wonder what this curious anatomy is for.

In contrast, when foraging on the Canada Goldenrod, the fly moved randomly, rarely spending more than a few seconds on any one frond.  Several species of bees were much more systematic in their search.  The difference could have something to do with proboscis or tongue length perhaps.

In contrast, when foraging on the Canada Goldenrod, the fly moved randomly, rarely spending more than a few seconds on any one frond. Several species of bees were much more systematic in their search. The difference could have something to do with proboscis or tongue length perhaps.

The larvae also perform a vital ecological service, as they parasitize some of the more noxious pest caterpillars — tent caterpillars, fall webworm, tomato fruitworm, corn earworm, and cutworms.  Adults lay their eggs on the underside of the host; when they hatch, the larvae burrow into the host and begin consuming it.  One less pest to worry about.

This shot provides a better idea of the fly's size relative to the central disc of a Black-eyed Susan flower.

This shot provides a better idea of the fly’s size relative to the central disc of a Black-eyed Susan flower.

Its features don’t inspire immediate affection, but the White-faced Fly is a beneficial insect nevertheless.

Symmetry

Most animals seem to be attuned to recognizing another individual’s symmetry as a means of judging its fitness as a potential mate. Among most human cultures, both men and women will usually choose the most bilaterally (equal halves) symmetrical face as the most beautiful. Thus, it’s no surprise that we humans prize the beauty of a highly symmetrical flower as well:  e.g., orchids, with their perfect bilateral symmetry, or dahlias, with their fascinating radial symmetry.

dahlia

dahlia

While plant breeders may have selected for the perfect radial symmetry of a dahlia, which we love to show off in our gardens, other forces were at work in the production of the spiral pattern of the seeds in a sunflower head, or disc flowers of the Black-eyed Susan, Purple Coneflower, and Sunflowers.

bumblebee-on-sunflower

Only one ring of yellow disc flowers are open for pollination at any one time.

Only one ring of yellow disc flowers are open for pollination at any one time.

purple coneflower

The arrangement of the emerging disc flowers is positioned so as to maximize their number in the available space.  When fertilized by pollinators, this will produce the maximum number of seeds per flower head — i.e., maximizing the fitness of that particular plant in its ability to pass on its genes.  To achieve this packing density, the disc flowers must lie at an angle of exactly 137.5 degrees from its neighbor, resulting in a series of spirals, rather than distinct horizontal or vertical rows. The same pattern is established in the growth of basal leaves of some plants (e.g., agave) and flower petals.

Chrysanthemum petals emerge in a spiral pattern, which reduces the overlap of petals in adjacent layers.

Chrysanthemum petals emerge in a spiral pattern, which reduces the overlap of petals in adjacent layers.

The spiral pattern is laid out with mathematical precision  — nature’s symmetrical design.  You can read more about the mathematical basis of the design in an earlier post.