Thursday, July 31, 2008

Freshwater mussels: overlooked, under appreciated residents of Illinois streams

Freshwater mussels: overlooked, under appreciated residents of Illinois streams

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If you’ve spent time canoeing or kayaking on rivers in the Midwest, you’ve probably come across the shells of freshwater mussels from time to time. On the outside, mussel shells are seldom pretty, but the pearly shine of the interior surfaces often prompts people to pick them up.

Scientists distinguish among different species of mussels by focusing on the shape of certain parts of the shell. Here, for example, is how the Field Guide to Freshwater Mussels of the Midwest (Illinois Natural History Survey: click here to see free online version) describes the appearance of a species that goes by the scientific name Quadrula quadrula: “Shell quadrate to rounded, and somewhat inflated. Anterior end rounded, posterior end squared or truncated.”

Now, if that doesn’t bring to mind a very clear picture for you, try the common name for the same species: it’s “mapleleaf.” [Photo of Quadrula quadrula by Kevin Cummings, from the field guide. It reminds me of a maple leaf, anyway.]

Other Illinois mussels carry similarly evocative common names, which tell both what the creatures look like and what objects were familiar to the people who named them. Among them some of my favorites are washboard, pistolgrip, wartyback, heelsplitter, deertoe, spectaclecase, and pocketbook.

According to Kevin Cummings, a mussel expert at the Illinois Natural History Survey on the U of I campus, North America is home to a greater diversity of freshwater mussels than any other continent, with nearly three hundred species and subspecies. Some eighty of these are or were once found in Illinois. Many mussels have become locally extinct in former habitats, and only about forty species are regularly found in the state now.

Freshwater mussels live a low-key life for the most part. They pass their days hunkered down in the sand or gravel, usually in flowing water. They feed on microscopic plant and animal life, as well as other tiny bits of organic matter, which they filter from water they take in through one siphon and eject from another. Mussels are fed upon by a variety of fish and birds, as well as muskrats, otters, and minks. Minks leave the cleaned shells of mussels they’ve eaten in a pile near the water’s edge called a midden, which can be a great place to find and identify shells.

The early development of mussels is a bit more complex and dramatic. Mussel eggs are fertilized within the female, with sperm that has been released into the water by nearby males. Inside the female, the fertilized eggs develop into larvae, which scientists call “glochidia.” To grow further, these glochidia must be expelled and attach themselves to the gills or fins of a fish for some weeks, where they will take on their adult form, in miniature, before dropping off to live at the bottom of the stream again. By sending forth their young attached to fish, mussels are able to disperse much farther than they would under their own power.

Over time, freshwater mussels have served a variety of human purposes. Native Americans ate their flesh and used their shells for utensils, tools, and jewelry. During the nineteenth and early twentieth centuries—before the advent of plastics—mussel shells were used on an industrial scale to make buttons. Since the 1950s, mussel shells have been exploited commercially for use in the production of cultured pearls in Japan.

It is unfortunate for mussels that they are not more cute and cuddly, because as a group they are among our most endangered animals, suffering from overexploitation, the pollution and physical degradation of waterways, and the introduction of exotic species to their habitats. Perhaps our best hope for preserving them comes from the growing awareness that the health of our rivers and streams is really a component of our own health.

Thursday, July 24, 2008

Illinois ash trees imperiled by imported beetle

Illinois ash trees imperiled by imported beetle

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If you’ve been struck by the odd sight of purple boxes tied to trees this summer you’re not alone. Those boxes are traps used by the Illinois Department of Agriculture to monitor the spread of the emerald ash borer, an insect native to Asia that was first detected in North America only six years ago, when it arrived in the Detroit area by means of wooden shipping material. (Click here to visit the information-packed IDA website devoted to emerald ash borer.) Last week brought the grim news that two emerald ash borers had been found in Bloomington, which represents the first appearance of the beetle so far south in Illinois.

Of course, many residents of Michigan, Ohio, Indiana, and northeastern Illinois have already experienced the devastation caused by the emerald ash borer. North American ash trees possess no natural defenses against this insect, which in its larval stage, feeds on the active layer of wood just beneath the bark of a tree, killing it by cutting off its supply of nutrients.

So far some 30 million ash trees have been lost to emerald ash borers in the Midwest.

In light of this development, I checked in with Jeff Dawson, a U of I professor in the Department of Natural Resources and Environmental Sciences, regarding ash trees and what they mean to people.

Dawson pointed out that although we tend to lump them together, five different species of ash trees, adapted to varying conditions of soil and climate, help to make up forests in Illinois. (Click here for a helpful online guide to ash identification.) The species that most people are familiar with as a shade tree is the green ash, originally an inhabitant of river bottoms. [Photo: A line of green ash trees shades Kenwood Road adjacent to Centennial Park in Champaign.] The adaptations that enable green ash trees to flourish in that environment also allow them to thrive near pavement and in the compacted soils typical of urban and suburban settings.

Dawson emphasized that ash wood is at once lightweight, strong, and flexible, making it useful for products ranging from tool handles and commercial flooring to canoe paddles, guitars, and of course baseball bats.

While it is important to delay the spread of emerald ash borer so that cities, forest preserves, and park districts can manage the enormous and staggeringly expensive task of replacing ash trees, no one anticipates an effective fix to this problem. Homeowners and others can preserve prized ash trees through the use of systemic insecticides, but such measures are not practical on a larger scale. It’s depressing to say so directly, but ash trees are likely to go the way of American elm trees and chestnuts within the foreseeable future. We’ll be able to grow them under highly managed conditions, but they’ll be lost as a functional component of our natural areas and a source of wood for many products.

What can we learn from this experience? For one, diversity is essential to the maintenance of urban forests. It is sad but true that some streets left devoid of trees with the loss of American elms a generation ago were replanted with only ash trees, and are thus once again starting from scratch.

The introduction of the emerald ash borer to North America also reminds us that globalization can entail great costs, both economic and ecological. Many forests will be forever altered without a healthy ash population, and many municipalities will struggle to pay the bills for ash removal and replacement in the years to come.

Finally, it’s important to recognize that individuals have an important role to play. We can slow the spread of emerald ash borer by purchasing firewood near where it is to be used rather than transporting it long distances. Emerald ash borers do not fly very far themselves, and by not giving them a lift we can buy ourselves important time.

Thursday, July 17, 2008

UI Extension’s new website provides information about coexisting with wildlife

UI Extension’s new website provides information about coexisting with wildlife

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I usually enjoy watching wildlife, but I’ve had very different feelings toward the rabbits in my back yard this summer. Feelings more like the ones people have toward squirrels at their bird feeders, or like Wile E. Coyote has for the Roadrunner.

That’s because my rabbits have been feeding on the new prairie plants I put in this spring. At first they ate a little bit of everything--just to figure out what they really liked, I suppose. Lately, though, they leave the butterfly milkweed and little bluestem alone while they repeatedly chew other plants to the ground. It’s as ifthey are waiting to pounce whenever the spiderwort or the black-eyed Susans send up even a hint of new growth.

I had these rabbits in mind recently when I received an email from Wildlife Extension Specialist Laura Kammin saying that the website she has been building is now online. The site is called “Living with Wildlife” and it is a project of the Illinois Department of Natural Resources and University of Illinois Extension. The purpose of the site is to provide people with information about Illinois wildlife, with an emphasis on animals that are adapted to life in urban and suburban settings.

So I surfed on over to find out what I could about coexisting with rabbits. Here’s what I learned.

The only kind of rabbits in my yard and most of Illinois are eastern cottontail rabbits. Cottontails are full size and sexually mature at just six months of age, and they really do breed like . . . well, you know. Female cottontails give birth to litters of four to six young as often as three times in a year. Good thing for them, too, because cottontails typically live only a year or so.

Some children, as well as adults of a certain sensibility, may be interested to learn that rabbits eat their own poop. After consuming your beloved plants they scamper off to a sheltered spot where they excrete lightly digested fecal pellets, which they then re-ingest for more thorough processing the second time around.

A fact that everyone should know about rabbits is that mothers leave their young alone in the nest on purpose, in order to not attract the attention of predators. So if you happen to find unattended baby rabbits it is important to leave them where they are—they do not need to be rescued.

How does one prevent rabbits from damaging plants? There are no easy, surefire answers to the question, but the “Living with Wildlife” website offers a number of possibilities. You can cut down on the amount of cover in your yard to make rabbits less comfortable there. And you can favor plants they don’t normally eat, although in tough circumstance they will eat just about anything. Or you can protect special plants with commercial repellents or wire mesh. My plan is to use domes made of hardware cloth to give new plants a fighting chance.

If you’ve got rabbit issues of your own, or questions about other animals, I encourage you to check out the “Living with Wildlife” website at [].