Sphagnum bogs, home of weird and wonderful creatures

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The Big Heath in Bass Harbor, MDI, Maine, is a good example of a northern sphagnum bog. Note the ericaceous shrubs in the foreground and the black spruce trees behind them.

Most of us have heard the term bog used colloquially to describe any wet, muddy area, but the true definition of a bog is a wetland that accumulates large deposits of dead plant material known as peat. Often this comes in the form of sphagnum, a genus of about 380 species of mosses that retain water especially well. True bogs are typically acidic and low in nutrients, and in many cases all water in the bog comes from precipitation. Most ordinary plants would die under these conditions, but of course there are quite a few that have adapted to these unfavorable circumstances, creating a distinct community of species that is nonexistent elsewhere. Unique plants, in turn, play host to unique insects.

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McLean Bogs in Tompkins county, NY, is an odd area containing a very small round sphagnum bog surrounded by glacial eskers.

I have had the fortune to be able to visit several sphagnum bogs in Maine and New York, and although each one has its own character, the same familiar plants and animals tend to greet me at every spot. The most obvious player is sphagnum moss, which forms a soft, spongy mat across every bog. When the mat is pressed, it gives up its water like a giant sponge, often evicting many small insects from their hideouts as they swim to safety. This is the primary way I find the dominant orthopteran inhabitant of eastern U.S. bogs, Neonemobius palustris. This tiny ground cricket lives exclusively in these habitats, and were it not for its song one would be hard pressed to detect its presence. Their tie to the sphagnum is quite obvious at the bog’s edge; there one can discern that where the sphagnum ends, the singing ends as well.

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A female nymph of the sphagnum ground cricket, Neonemobius palustris (McLean, NY).

Before I visited bogs to look for insects, I visited them to see a very special group of plants: the carnivorous plants. These unbelievable organisms that have to be seen to be believed only grow in places extremely deficient in nutrients, such as bogs or rock outcrops. They make up for the lack of soil nutrients by capturing and digesting insects and occasionally other small animals. Carnivory has apparently evolved independently in 9 different groups of plants, and thus there are a wide range of different prey capture strategies. The most well-known is the snap-trap of the venus’s fly trap (Dionaea muscipula), but that species is restricted to bogs in North and South Carolina (it is also widely cultivated in captivity). The types found in most eastern sphagnum bogs are several species of sundews and pitcher plants. Sundews (Drosera), which I surprisingly have no good photos of, consist of flattened leaves with hairs that bear drops of sticky sugary liquid on their tips. These attract insects, which get stuck and are eventually digested by the plant. Pitcher plants (Sarracenia), in contrast, are literally pitchers of liquid containing nectar bribes that lure insects to the edge, where they fall in and cannot escape. I am always guaranteed to see these fascinating little plants every time I enter a sphagnum bog.

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Northern pitcher plant, Sarracenia purpurea (McLean, NY).

Although carnivorous plants may seem to have turned the tables on insects, some insects have turned the tables again and evolved to take advantage of their captors. Wyeomyia smithii mosquitoes only breed in the pitchers of pitcher plants; moths of the genus Exyra feed exclusively on pitcher plants; Buckleria parvulus plume moth caterpillars feed on the sticky glue of sundews; Camponotus schmitzi ants are known as diving ants because of their habit of diving into the pitchers of pitcher plants and retrieving the plant’s food items. Unfortunately I have never had the good luck to encounter any of these tricky little animals at work.

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Lichnanthe vulpina, the bumblebee scarab. A member of the family Glaphyridae (once part of Scarabaeidae), this animal looks uncannily like a bumblebee in flight. Another name for this species is cranberry root grub because the larvae feed on the roots of cranberry plants (Kennebunk, ME).

Sphagnum moss and carnivorous plants are not the only plants present in bogs. Many specialized sedges and orchids live in bogs, as well as plants of the family Ericaceae (which includes such things as heaths, heathers, blueberries, and cranberries). Heaths are often host to some very strange insects, such as Lichnanthe vulpina, a bee-mimicking scarab beetle. Most trees cannot survive in bogs, but black spruce (Picea mariana) and tamarack (Larix laricina) often invade the open bogs, albeit in stunted form.

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Tamarack (Larix laricina), a common bog tree. This is a highly unusual tree that is a deciduous conifer – that is, it has all the characteristics of typical evergreens such as pines and spruces, except it loses its needles every fall! This photo was taken in October (Saco, ME).

If you have never experienced a bog before, do yourself a favor and visit one. Many bogs have boardwalks through them to facilitate public encounters, since walking directly on the sphagnum tramples and destroys the rare plants there. There are tons of awesome organisms in bogs, and I have only attempted to depict a few of the most interesting ones that I have seen here.

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The Saco Heath, a large bog open to the public with a long boardwalk. The white tufts are the seed heads of cotton grass (Eriophorum), a characteristic sedge in bogs.

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Getting their Feet stuck in the Milkweed

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Odontomyia cincta from Kennebunk, ME.

A few days ago I discovered a contender for the most colorful fly in my yard (Idana marginata is a serious competitor for this title): Odontomyia cincta. With lovely orange legs and a body pattern of black and brilliant green stripes, this is one beautiful animal. Most people would probably be surprised to learn that this is a fly at all, given the popular image of flies as dull-colored disease-spreading organisms. I see Odontomyia off and on in my yard, usually either sitting on leaves or nectaring on the dogwood that is flowering in my front garden right now. The genus contains about 31 species in the U.S, and adults are found in woodlands and fields near freshwater habitats, where the young develop. The larvae are “butt breathers” that stick the tip of their abdomen through the water’s surface to obtain air while they graze on algae underwater.

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Odontomyia trapped by its tarsi in a milkweed flower. Note the bright orange pollinia (Kennebunk, ME). And yes, I freed it after taking its photo.

Although these are interesting animals in themselves, I was reminded of an even more interesting phenomenon I observed a few years ago that involved Odontomyia. While out “bugging” in a large open field, I stumbled upon quite a few individuals of Odontomyia in a patch of common milkweed. All were trapped by their feet (tarsi) by the milkweed flowers. Nor were they alone – I observed at least three other insect species that had encountered the same problem. Some had managed to escape the flowers’ grasp, while others hung helpless, trying in vain to extricate themselves. What was going on here?

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Common Milkweed (Asclepias syriacia)

Common milkweed (Asclepias syriaca) is an amazingly interesting plant native to southern Canada and most of the eastern U.S. It is perhaps most well known as the houseplant for the Monarch butterfly, but it is also host to many other specialist feeders, including two seed bugs, several beetles, and a tiger moth (idea for a future blog post!). When a leaf is broken, a milky substance oozes forth (giving the plant its name), which contains toxic cardiac glycosides that can kill or incapacitate most vertebrates, including humans. These chemicals do not harm the specialist insects that feed on the plant, of course. But it is not only the leaves that pose a threat to other organisms. The large masses of pink flowers contain structures that contain pollen in little packages called pollinia. When an insect brushes against one of these structures, the pollinia clamp onto its leg or proboscis. The idea here is that the insect will break off the pollinia and then visit another milkweed flower, thus completing the process of pollination. However, many insects simply don’t have the muscle to break off the pollinia, and thus end up, like the Odontomyia, stuck helplessly. Only the strongest of insects, such as bumblebees and monarchs, can break loose. Despite the dangers involved, the nectar of milkweed flowers must be very attractive to insects, as individuals that have managed to escape the flowers often return. The fact that the milkweed flowers end up killing quite a few insects does not seem to have any benefit to the plant; it is not carnivorous. Perhaps the decaying insect carcasses, when they finally fall to the ground, provide nutrients to the soil surrounding the milkweed. Something interesting to look into. In any case, yet another reason I’m glad I’m not an insect. Otherwise I’d have to worry about being snared in a bear trap every time I eat something.

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One that didn’t make it: an unidentified fly hanging dead from a milkweed flower, with numerous pollinia attached to its tarsi.

Reference:

Frost, S. W. (1965). Insects and pollinia. Ecology, 46(4), 556-558. Retrieved from http://www.jstor.org/stable/1934896?seq=1