Thursday, July 21, 2016

Annual cicadas enliven dog days with love song [from the archive]

Annual cicadas enliven dog days with love song

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Even if the heat and humidity of recent weeks have limited your time outdoors, I bet you’ve been hearing a familiar insect song. It’s the mating call of dog day cicadas, loud enough to rise above the drone of air conditioners and so persistent and widespread that people who hear can hardly miss it.

I say, “dog day cicada” I mean the insect (pictured right) that goes by the two-part scientific name, “Tibicen canicularis,” which is the most common species of forest dwelling cicada that occurs in the eastern U.S. and Canada, one that has also adapted well to life in urban and suburban settings where enough trees grow to support it. These cicadas have bulky, bodies about an inch and a half long that are dark on top with green and white markings, and entirely white below. At rest their clear, heavily veined wings close over the back like a pitched roof and add another half inch to their length.

Some people call these and other cicadas locusts, a name that was first applied to them by settlers of European extraction for whom the emergence of large broods called to mind the plagues of the Bible. But the name locust is more properly applied to certain grasshoppers. Other people know cicadas by the name “harvestfly,” which derives from the fact that they emerge as adults at the same time crops are maturing.

The singing of dog day cicadas is one of the loudest insect noises on earth, sometimes exceeding 110 decibels up close. This means the song of a cicada perched your shoulder would be plenty loud to damage your hearing. The song is often compared to the whirring of a circular saw, although I think that comparison ought to be reversed, since cicadas have been around far longer than power tools. The earliest fossil record of a cicada dates back 65 million years.

[Photos by author: above, cicada "singing" on a tree trunk; below, newly captured and paralyzed cicada in the grip of a cicada killer wasp.]

The fact that dog day cicadas are also called annual cicadas sometimes generates confusion about their life cycle, but do they live for more than a year. They start out as tiny nymphs, which hatch from eggs laid in tree branches. These nymphs drop to the ground and burrow down to find a root they can latch onto for nourishment, and there they remain, probably for something like two to five years. (Scientists aren’t sure exactly how long, and the span probably varies according to conditions affecting the cicada’s development.) Some annual cicadas emerge as adults each year because their generations are staggered, which sets them apart from periodical cicadas, generations of which mature in synch, on 13- and 17-year cycles.

It is a common misperception that adult cicadas do not feed, but the fact is they have all the mouthparts needed to extract liquid from plants, and they’re not afraid to use them. Dog day cicadas do no damage to trees as they feed, and no measures to control them are warranted.

The only warm-blooded predators that pose a significant threat to cicadas are birds, but there’s another insect that specializes in them, the cicada killer wasp. A female cicada killer stings a cicada to paralyze it, then carries it back to her burrow still alive. There she seals the unlucky creature in a chamber with one of her eggs, to become nourishment for the grub that hatches.

But that’s not where I want to leave you. Let’s get back to cicadas singing their love song in trees, and appreciate how that enriches our summer.

Thursday, July 14, 2016

Freshwater mussels: overlooked, under appreciated residents of Illinois streams [from the archive]

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 07, 2016

Thirteen-lined ground squirrels (not chipmunks, not gophers) [from the archive]

Thirteen-lined ground squirrels (not chipmunks, not gophers)

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My encounters with ground squirrels in the west this summer reminded there’s a common, yet fascinating animal closer to home I’ve been meaning to profile, the thirteen-lined ground squirrel. Do you know the one I mean?

If you’ve had a small squirrel dash in front of you as you drove on a country road bordered by crops, or you’ve seen a chipmunk-looking critter darting about in a cemetery, you’ve probably encountered a thirteen-lined ground squirrel. Some people call thirteen-liners gophers because they live in the ground, but in scientific terms, they’re members of the squirrel family.

Thirteen-lined ground squirrels are among those animals that have benefited from human development because they thrive in the close-cropped landscapes we create, from roadsides and pastures, to cemeteries, golf courses, parks and other lawns. Their geographic range, which encompasses much of the central U.S. and Canada, has actually expanded over the past two centuries.

If you were to draw a thirteen-lined ground squirrel based on its name, you would produce a picture that left out a notable characteristic of the original. Yes, they are marked by about thirteen alternating stripes of dark brown and light tan fur that run from neck to tail. But what’s equally striking is that the wider, dark lines are decorated along their entire length with evenly spaced light dots, giving them a star-spangled appearance. There’s a golden tinge to some of the lighter fur on thirteen-liners, and they’re the creature on which the University of Minnesota’s Golden Gopher mascot is based.

Thirteen-lined ground squirrels eat just about anything they can get their little paws on, from insects of all sorts to the occasional small vertebrate (including carrion), to grasses, flowers, seeds and crops. They have pouches in their cheeks that they use to transport food to their burrows for eating later. (If you have trouble with thirteen-lined ground squirrels eating from your garden, University of Illinois Extension’s “Living with Wildlife” Website provides suggestions for dealing with them:

Thirteen-lined ground squirrels are, in turn, food for a wide range of other animals, including coyotes, foxes, weasels, dogs, cats, hawks, owls and snakes.

One way thirteen-liners avoid being eaten is by excavating short, shallow escape burrows throughout their territories, so they’re never far from a hole to dive into. They also create deeper, longer burrows for nesting and hibernating.

And thirteen-lined ground squirrels hibernate like champions. After fattening up in the Fall, they retreat to a chamber that’s below the frost line, plug the entrance with soil, and curl up for about four months. During hibernation—which begins in late October or early November and lasts until late March or April—their body temperature nearly matches the temperature of the burrow, dropping as low as 37 degrees F. By the time thirteen-liners awaken, they have lost up to half of their body mass.

During the months thirteen-lined ground squirrels are active, you need not get up early to see them, nor do you need to brave inclement weather. They are most active on warm, sunny days, and they don’t even bother coming out of their burrows in the rain.

To learn more about thirteen-lined ground squirrels, or any of the other mammals you might see when you’re out and about in the Prairie State, let me refer you to the source for much of the information in today’s commentary, the Field Manual of Illinois Mammals by Joyce E. Hofmann. It’s published by and available through the Illinois Natural History Survey, which is a division of the Prairie Research Institute at the U of I in Champaign.