Prairie parkland landscapes are at their peak golden color now. The fall landscape is transforming daily, and with the nice fall weather lately, it’s a glorious time to be out walking around. I’ve given up trying to find the migrating birds at this points and am just enjoying the golden colors everywhere.
In the Minnesota backyard, some of the summer blooms are in their full glory, particularly the purple coneflower. Butterflies and bees are drawn to these flowers…
Although we have been a little early in some places and a little late in others, we still have seen some of the spring wildflower show as we travel.
After four days of the white stuff raining down on us, I need a shot of color from the brilliant hues of this past Fall season.
One way to ensure seed set in a plant is to capture as many pollinators as possible, and this seems to be the strategy influencing the flowering times of Goldenrod and Aster species. By blooming so late in the summer and early fall, they are pretty much the only pollen and nectar sources around.
And to ensure that bees do visit their copious numbers of flowers, the plants need to advertise themselves with the colors that are most attractive to bee eyes — yellow-green and blue-purple. Bees also key in on light that is a combination of yellow and ultra-violet, something humans can’t detect, but probably marks landing platforms or serves as nectar guides on flowers.
Walking around Tamarack Nature Center in White Bear Lake, MN the other day, I saw some unusual plants in wetter patches of the prairie.
Although the flowers look like buds that aren’t yet open, this is the typical mature flower presentation with its petals closed up tight.
You have to wonder how or whether such a flower can get pollinated. But it turns out that this plant is very particular about which pollinators it allows to perform the pollination service. In this case, it requires large-bodied bumblebees that are strong enough to separate the tips of the petals so they can crawl into the flower to pick up the pollen and nectar within.
As the bumblebee enters the flower, it pushes its thorax against the flower’s reproductive parts, rubbing pollen onto the exposed stigma, pollinating it. By vibrating its wings and body inside the flower, the bee causes that flower’s anthers to release pollen onto the surface of the bee, which it combs off into pollen sacs later. The nectar is located at the base of the flower, so again, it requires a large bee with a long tongue to reach the nectar source.
In the video below, you can see how hard the bee works to get into the flower and hear the buzzing while the bee is completely encased by the flower. (Video by NaturalistDave Nature Video)
Typically, the bumblebee will visit just one flower of the group at the tip of the plant, moving to the next plant after exiting a particular flower. This ensures the cross-pollination which is required for seed set. When pollinators are excluded from these flowers, only 4% of the flowers were able to produce seed, but when pollinators were allowed, 96% of the flowers produced seed.
Why would bumblebees go to all this work to get into such a tightly closed flower, when there are so many other flowers with nectar and pollen to harvest in the prairie? Or are there?
While waiting for the hummingbirds to show up to have their photos taken last week, I got plenty of time to watch some insect pollinators in action. Some plants are obviously not fussy about what or how many pollinators they attract, so they put out a vast array of flowers — like a buffet table.
But some plants are fussier about which pollinator they cater to and which they can physically exclude. It was amusing to watch several different bee species work the plants with tubular flowers, especially the ones with deep necks, like Salvia and Bee Balm.
Sometimes smaller is better, as far as pollination of the flower is concerned, because the smaller honeybee does a better job of contacting the flower’s reproductive parts and transferring pollen from one flower to the next.
Lobelia flowers were a perfect fit for the smaller worker bumblebees, but that didn’t keep larger-bodied bumblebees from trying to get its nectar.
This bumblebee is too big to fit into the flower opening, while another, smaller worker bumblebee, (below) crawls right in. And notice how nicely that smaller bee contacts the protruding (white) stigma (the female reproductive part) of the flower as it enters and exits. No doubt this bee will transfer pollen effectively.
Meanwhile, tiny little forget-me-not flowers, with their miniscule central opening, require the services of small bees with slender tongues to reach the chamber with the nectar. Sweat bees are just the right size, and I found two different species hovering and probing the flowers.
You’ve seen how busy bees gather pollen from some flowers — for example, they systematically crawl over the surface of Coneflowers and Black-eyed Susans, the tops of which are dotted with little ray flowers sticking their pollen up for grabs as the bee comes by. Many different kinds of pollinators might walk around picking up pollen from these plants, so there is lots of competition for the pollen. But there is no guarantee that they will deposit any pollen on a nearby neighbor — they might just fly off to a completely different group of flowers instead.
Other flowers present a nectar reward to the bee if it will kindly crawl into the tubular flower, brush against the anthers to receive pollen and then kindly deposit that pollen in another of the same type of flower they subsequently visit. But who knows which flowers the bee might visit next — it might not be the same species at all.
Still other plants produce flowers that protect their pollen for just the right pollinator, one that specializes in picking up pollen from particular a species, and reliably deposits some of that pollen on a neighbor of the same species for some healthy cross fertilization.
By locking the pollen up in a capsule, it is protected from just any random pollinator walking over the flower. Shaking the flower might dislodge some of the pollen, but most pollinators can’t manage that. Instead, bumblebees and some solitary bees grasp the anther capsule with their legs, or even mouthparts, and vibrate their wings at a very high (and audible) frequency — and pollen comes flowing out the pore at the end of the capsule, dusting the bee. This technique is referred to as “buzz pollination”.
The video below illustrates the bumblebee action nicely:
“much of the food we eat owes its existence to the buzz of the bumblebee”
It’s prime time for summer flowers, and the bumblebees and honeybees are making the rounds carrying pollen from one flower to another and sipping nectar as their reward.
If you’re always looking up to find the birds in the trees, you might miss something interesting on the ground by your feet. And indeed, I almost stepped on this huge 2- inch long Elm Sawfly that really isn’t a fly at all.
One might wonder why a bee would be called a fly — and there isn’t any logical explanation except that the female uses her ovipositor (at the end of the abdomen) like a saw to open cavities in an elm leaf in which she lays about a dozen eggs. Then she moves onto other leaves and does the same thing, until she has deposited about 150 eggs. Whitish larvae hatch out and like all sawflies, immediately begin consuming the vegetation, growing about two inches in a month of eating, until they return to the soil to pupate over the winter. An infestation of sawflies on a young tree may defoliate it so much that the tree becomes stunted, or even dies.
These insects are probably not very numerous in this part of Minnesota since Dutch Elm disease has wiped out so many of their potential host plants. In addition, both the eggs and the larvae may be parasitized by small wasps and never make it to the pupal stage. If they reach the pupal stage in the soil, they may be preyed upon by shrews and deer mice, so seeing one just sitting on the trail might be a rare event.
We made a brief trip up north over the July 4 holiday to lovely Maplewood state park, about a 3-hour drive northwest of the Twin Cities. Lakes, trails, great campsites, rental canoes and kayaks available, swimming beach, wildlife, and more. What a beautiful place, and it must be even more so in the fall, when the maple-basswood forest has turned gold and red.