Alas, September is our last summer month. Although temperatures have been falling since mid-July, the metabolism of the forest continues to breath in and out through photosynthesis and respiration. Next month is when our Gaian natural world shuts down its engine and moves into winter mode.
September is the time of fruiting for many plants. Ginseng, with its bright red berries, is traditionally harvested at this time. The white-fruited doll’s eye also stands out. Whether these highly toxic white fruits with the black ends were really used for doll’s eyes, I don’t know, but I hope it is only apocryphal. And, if you haven’t tried paw paws, look for them along the Potomac River, or in your larger farmers markets.
For the most part, only the most advanced of the dicot plants, belonging to the Aster family (Asteraceae), produce many members that flower during this month, including numerous asters, goldenrods, ironweeds and Eupatoriums, including Joy-Pye weed, white snakeroot and the bonesets. Their ability to produce fruits in less than a month enables them to take advantage of the pollinating insects that still dominate in September.
To pollinate these late season flowers, many butterfly species have a second brood, or even a third brood, including most swallowtails, red-spotted purples, silver-spotted skippers, fall webworms and the carnivorous harvester butterfly. This last butterfly is our only carnivorous species as well as the only species in the harvester family (all others are found in Asia and Africa). Caterpillars consume aphids or other small insects where their eggs have been laid, and adults feed only on aphid secretions, rather than flowers.
September is the season of the fall bird migration. That means the confusing fall warblers, among others. Perhaps of more interest to many of us, is the ridgetop migration of hawks. In addition to Hawks Gap and Waggoner’s Gap in PA, birders are found daily in the fall at Snickers Gap, at the Route 7 crossing of the Blue Ridge in VA. Snicker's Gap is at its best from September 14 to 21 when thousands of migrating broad-winged hawks stream past overhead on a good day. Migrating bats, butterflies and dragon flies can be observed here as well.
Wasps, bees, and ants; the social insects of the order Hymenoptera, undergo their mating rituals in September. Throughout the year, these colonial insects, including paper wasps, yellowjackets, hornets and black carpenter ants, have consisted only of females, obtaining food, fighting enemies, caring for the queen and raising more females. Now, through a change in diet, initiated by decreasing sunlight, the queen’s eggs yield males and queens who, after metamorphosis, leave the nest in swarms of flying masses. The males grasp the queens and mate with them, falling to the ground. With the wasps and bees, only the mated queens will overwinter to start new colonies in the spring; all female workers and males perish. In the case of ants, many of the female workers survive the winter underground. Mated queen ants are either taken back by the overwintering females or overwinter on their own. In all cases, the males are short lived, serving their purpose and then simply starving to death.
While many spiders mate in the fall, then perish, leaving only an egg sack to overwinter, some young spiderling species at this time of the year go ballooning on gossamer strands of silk. This allows them to scatter by the winds to new territories for overwintering and colonization. Most of the ballooning spiders are of the family Linyphiidae, some species so common that hundreds of thousands of them may live on an acre of land.
September is a month of preparation for the mammals of our forests. White-tailed deer fawns lose their spotted summer coats, molting into a drab winter brown coat. Adult bucks will be rubbing off the velvet from their completed antlers, with the tearing and scraping of many small trees and shrubs being found along hiking trails.
By the end of this month, our true hibernator, the ground hog, or woodchuck, succumbs to the desire to sleep. While there are many adaptations to survive the winter season, only the groundhog, jumping mice and some bat species exhibit what we would call true hibernation (some experts will include chipmunks in this category). During hibernation, the groundhogs body temperature drops from 98° F to about 40 - 47° F degrees, heart rate drops from 100 to four to fifteen beats per minute, respiration rate drops to one breath per three or four minutes. True hibernators must wake every month or so during the hibernating period to defecate and to exercise the brain.
Black bears are said not to truly hibernate, because, although their bodily processes are slowed, they are not suppressed to the extent found in the deep hibernators. Their body temperature decreases from 100 to 91, heart rate dropping from 45 beats to 13 per minute, and breathing is only two to four times per minute. September finds black bears quite mobile, looking for food sources, such as apple orchards or cornfields, waiting for the oak acorn crop to mature. They will not enter their winter dens until late November or early December.