A sunflower (Helianthus spp.) in my garden illuminated by the sun. Photo by Donna L. Long.

Fall Sunflowers, Bees, Flies and Pollination

 

A sunflower in my garden illuminated by the sun. Photo by Donna L. Long.

From my nature journal for 28 September 2015

In the last day of summer and the first days of fall, sunflowers bloom in my garden. The flower petals glow golden-yellow in the sun. These autumn blooming flowers provide food, pollen, nectar and prey to visiting insects and resident spiders. I stood and watched several species of bees, flies, and tiny winged fliers too small to identify with the naked eye. The bee tribe was well represented with Bumble bees, Eastern Carpenter Bees, and Cuckoo Bees in attendance.

 

Young green parts of a sunflower (Helianthus species) blossom. Photo by Donna L. Long.

 

Inside a sunflower (Helianthus spp.) blossom in my garden. Photo by Donna L. Long.

 

The spent flower head of a sunflower (Helianthus spp.) in early autumn. Photo by Donna L. Long.

The deep golden blossoms are mostly spent. A few blossoms with bright green centers of the young, are here and there on the five foot tall plant. The rest of the blossoms are deep golden brown, drying out, and fertilized. The fertilized blossoms are busy developing seeds. The height of activity on the plant was in the last three weeks.

The last of the flowers permanently face west in my garden, toward the setting sun. This movement toward the sun is known as heliotropism. the flowers facing the sun are warmer which is an advantage for the insects that visit the flowers. The insects don’t have to spend precious feeding time, basking in the sun to warm up. They can feed and bask at the same time. And the extra warmth speeds up seed development. As sunflower blossoms mature, the heliotrope behavior stops as the young flexible flower stalks stop elongating and harden in place. A few late blossoms are still green inside. As I peer inside the blossoms with my hand lens, I see the curled ends of the stigma of the flower. The ends curl back in little curlicues signaling that this stigma is fertilized and on its way to making seeds. With my hand lens I see the silken strands of a spider’s web. Stuck on the silk, are bits and pieces of tiny insects, a leg, a bit of wing. Someone used the nectar and pollen of the sunflower as a way to trap a meal.

Eastern Carpenter Bee (Xylocopa virginica) busy at work in a sunflower blossom in my garden. Photo by Donna L. LOng

This late in the blooming phase, few insects visit the sunflowers anymore. They have moved on to the New England Aster a few feet away which is just coming into full bloom. The sunflowers have the smaller bees and flies still seeking nectar and pollen. The big bees – the Bumbles and the Eastern Carpenters are all on the asters.  Last week the big bees were on the Sedum ‘Autumn Joy’ I have planted across the garden.

Female Sweat Bee (Sphecodes species) in a sunflower blossom in my garden. Photo by Donna L. Long.

Several species of bees are on the sunflowers including Sweat Bees of the Augochlorini tribe, Cuckoo Bees (Sphecodes species) and Bumble Bees (Bombus species). All are native bees. I didn’t see any non-native honey bees. The Cuckoo bee is a small (1/8 – 5/8″) solitary bee the lives throughout North America. The Cuckoo Bee is a species of Sweat Bee. There are about eighty species of sweat bees in North America. The Cuckoo Bee in this photo is a female which sports a partially or entirely red abdomen while the male of the species has a black abdomen. Cuckoo Bees are solitary bees who don’t live in colonies with other bees or make nests off by themselves. Like the Cuckoo bird, the Cuckoo bee female lays her eggs in the nest of other sweat bees, while sometimes destroying the host’s egg. The Cuckoo’s egg hatches and the larva feeds and grows on the food gathered by the host bee.

Fly (?) in a youngish sunflower blossom in my garden. Photo by Donna L. Long.

The small green fly looks like a small green bee but I think it is a fly.

A small green fly at work pollinating a sunflower (Helianthus spp.) in my garden. Photo by Donna L. Long.

 

In this photo it is easy to see that this is a fly. Flies have two large eyes near the front of their heads which meet at the top. Bees have large eyes on the sides of the head.

When deciding whether an insect is a fly or a bee look for:

  • Flies have two wings, bee and wasps have four wings
  • Flies are usually less hairy than bees
  • Flies have large eyes on the front of their heads which often meet at the top; Bees have large eyes on the sides of their heads which don’t meet at the top
Sunflowers (Helianthus spp.) facing west in my garden in the early autumn afternoon sun. Photo by Donna L. Long.

 

The delicate golden yellow petals of a sunflower (Helianthus spp.) in my garden. Photo by Donna L. Long.

The New England Asters have just come into bloom. I eager to see what I find.

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