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A Fall Nectar Feast

As fall tightens its grip on the land and we begin to feel the nip of the fast approaching frost, who would think about flowers providing nectar to insects? Yet this can be a time of plenty and a furious pace of nectar gathering occurs among the insect world. Of course there are particular native flowers that bloom this time of year that provide sources of nectar- in our area especially asters, goldenrod and some lobelias. Since they are the last of the current growing season I think we cherish them even more than the more bountiful and diverse flower crops of summer.

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One of the characteristic but rare fall flowers of our farm is the stiff gentian- this is one of the so-called closed flower types and you might wonder why any flower would make it so difficult for pollinators to enter? The answer appears to be that the flower is thereby limiting pollinators to bumblebees which are strong enough to push into the flower to get pollen and nectar. Such specialization has been selected for by evolution to increase the efficiency of pollination. Thus the fly shown sitting on this gentian has no chance of getting any nectar. Some bees have tongues too short to reach the nectar and may bite into the base of the flower corolla tube to steal nectar without any chance of pollination.

 

A completely opposite strategy of flower pollination is shown by the numerous asters, which have flattened flowers which allow virtually any insect to land on them and probe for nectar. Here I show a clouded sulphur butterfly feeding with its very long proboscis which is certainly not needed to feed on this flower. Similarly a monarch butterfly is shown feeding on an aster flower in our fields. Dave Clayton sent me an interesting photo from the southern New England coast showing monarchs feeding on flowers of salt bush, also in the aster family but a weedy shrub usually considered to be of little use to butterflies. This illustrates how plants may often be of benefit to wildlife that are considered by humans to be undesirable weeds.

 

Bumblebees have high energetic needs and can be observed to be almost frantic in their efforts to gather pollen and nectar in fall. Our giant lobelias are just at the end of their flowering season and bumblebees are often seen visiting the flowers and pushing in to access the nectar. There are many species of bumblebees- some are small, some are larger and they have different lengths of their tongues. In this case the bee is almost too large to enter the flower and causes the petals to separate as it enters. It is quite interesting to look carefully at bumblebees as they forage on various types of flowers. For example I noticed that a large non-native Abelia bush attracted many bumblebees but they did not enter the flowers but stole the nectar by biting through the base (see photo). I observed the same process when bumblebees foraged on non-native black and blue salvia- they grasp the flower with their legs and bite the base and presumably suck out nectar which otherwise they could not reach since the flowers are too small for them.

 

If the sole purpose of flowers is to reproduce the species, and the offer of nectar rewards is designed to attract pollinators that will fertilize and cross pollinate the flowers, nectar thieves are a big problem in that they are in essence parasites on the plants. If you begin to watch flowers more carefully, you may observe a lot of this type of behavior- insects being excluded from flowers but finding a way to steal nectar anyway. This behavior is not exclusive to insects; birds are well known to engage in nectar theft. I noticed an example at our Florida home when birds are migrating north in spring. This photo shows a female orchard oriole stealing nectar from a non-native Cape honeysuckle flower by piercing the base. The birds that normally pollinate this flower from South Africa would be sunbirds which have a curved bill that fits into the flower perfectly. There are also birds in South America called flower piercers that even specialize in this type of behavior. There are many examples in nature of behavior which we might consider "unethical" (vines climbing up trees to reach the sun without growing their own trunks or parasitic mistletoe plants stealing nutrients from their hosts), but there is no good or bad behavior in nature, only adaptations leading to more successful reproduction of the species. Since there are no jails for insect bad boys, it is quite interesting to observe how plants respond to nectar stealing thieves.

 

Bill Dunson
Galax, VA & Englewood, FL

wdunson@comcast.net

http://www.galaxgazette.com/blogs

http://lemonbayconservancy.org/dunson_archives.htm

http://lemonbayconservancy.org/wildflower.htm