Natural Signs of the Approaching End of Summer

In mid August natural signs tell us without looking at a calendar that the end of summer is coming. Nights are cooler here at the farm (55F this morning), few birds are singing and some have left us on migration while others are beginning to migrate in from the north, fall fruits are ripening, late flowers are blooming, spiders are maturing and laying eggs, and so on. It can be an exciting time of year with a great deal of activity in the natural world, even if the marvelous sounds of spring have dimmed.

We have two wild magnolias that mature their fruits this time of year, the cucumber and Fraser magnolias, which produce numerous red/orange seeds which are highly attractive, especially to migrating thrushes. I attach a photo of the cone of the Fraser magnolia that is bright red with red/orange seeds. This color scheme is rather interesting since the cone itself advertises by color to attract birds from a distance; then the bright seeds direct the birds to a food reward for eating and dispersing the seeds. The seeds also fall from the cones and can be picked up on the ground. So there is a two stage process of attracting seed dispersal agents. Yet these magnolias are not always appreciated for their excellent food value for wildlife.

A fruit that is well known to most people is the may apple which blooms in the spring but sets fruit in late summer. Plants must have two leaves to bloom and the leaves and green fruit are protected by toxins. The ripeness is indicated by the yellowish color which is likely designed to attract mammals on the forest floor. As is the case for most poisonous fruits, they become palatable when ripe. There would be no point to providing a food reward for animals to eat a fruit and disperse the seeds if the result were death or sickness. But it is definitely in the interest of a plant to prevent the eating of the green fruit before the seeds are ripe, or to discourage the eating of any seeds. This explains why the ripeness of fruits is indicated by changes in color and taste, and why seeds themselves are often toxic and remain so inside a protective husk even when the fruits are ripe. They pass through the digestive system of the frugivore unharmed, are dispersed away from the parent plant, and are typically stimulated to germinate by this process.

An unusual sight in one of our flower beds mulched with wood chips was the appearance of a bright yellow blob which appears to be the famous dog vomit slime mold. Slime molds are not true fungi; the plasmodium creeps along very slowly much as an amoeba does and engulfs its food which is mainly bacteria. Such a strange organism tends to freak people out but it is harmless and in fact can be eaten, although it is not recommended.

Another creature that freaks people out is the spider which has few friends. Yet without them we would be inundated with all sorts of harmful insects. I have noticed that we have considerable numbers of the dark fishing spider, often far from water. This female had a nursery web next to a pond and is tending hundreds of babies. Although as humans we tend to think that maternal care is an altruistic trait mainly found in higher animals, such of course is not the case. Care of the young is a very selfish trait and quite primitive since its purpose is to protect the genetic heritage of the female’s progeny. Another interesting facet of this nursery web is that the baby spiders group together in a ball, presumably for protection; the sheer numbers are similar to a school of fish in that a predator would find it difficult to pick out one tiny spider to attack. The aggregate group of spiderlings may also discourage some predation due to the size of the group.

For years we have tried to grow orange butterflyweed without much success since it appears to be a poor competitor if dense grass or weeds are present. A hay field was mowed in mid June which apparently released a group of these milkweed plants from competition and five clumps of butterflyweed grew and are flowering now in mid August, later than the natural stands nearby. They have attracted many butterflies, including here a male monarch and a female spicebush swallowtail. This plant provides both nectar and larval food for the monarch including protective chemicals against predation (advertised by the bright colors), but only nectar for the spicebush. The spicebush swallowtail is one of a number of confusing “black and blue” butterflies that mimic the toxic pipevine swallowtail. Can you tell them apart (pipevine, spicebush, black, and black tiger swallowtails; red spotted purple; female Diana fritillary)? I am sure that birds must have a problem in distinguishing the edible from the toxic also- thus providing an evolutionary advantage for this mimicry complex.

I have noticed an interesting large fly near our wooden outbuildings. This tiger bee fly is unusual looking and has a strange life history. It is a parasite on the large carpenter bees that are so hated by homeowners since they drill holes in houses and barns. So here we have a beneficial fly that is reducing the number of carpenter bees that will emerge from their tunnels. So do not swat that particularly evil looking fly! Isn’t there is a certain satisfaction that even insects are plagued by other insects!

I miss the clamor of amphibians this time of year although I still hear an occasional call from bullfrogs and green frogs. The huge numbers of spring peepers that I know must be present in the woods are virtually silent. But rarely I come across a peeper in the woods- here a half grown juvenile was found by chance on a leaf. There must be thousands more dispersed all around.

Our many planted arrowwood virburnum bushes have thrived and have now produced many small bluish berries. Birds are very fond of these although they are not as obvious as red berries, nor do they appear very appetizing. What has surprised me is that flycatchers, such as this eastern kingbird, gorge themselves on these berries, despite the presence of numerous insects all around. There is I am sure a nutritional reason for this circumstance but I do not know precisely what energetic requirement is met by these berries. But I can highly recommend planting them in your yard.

Everyone loves bluebirds because of their beautiful colors and song, and their use of our yards and fields to breed. I am very impressed by their persistence in breeding- they start early and continue to breed for a prolonged period. I did a check of our 24 nest boxes recently and found these half grown baby bluebirds as likely the last of perhaps three broods their parents produced this year. Yet the tree swallows that compete for the same nest boxes/cavities generally have only one brood in this area. Why are such different strategies successful in the same habitat?

If nature does not surprise you at every turn, it is only because you are not being very observant.

Bill Dunson, Englewood, FL & Galax, VA
wdunson@comcast.net

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