Thursday, June 25, 2015

Appreciating common snapping turtles

Appreciating common snapping turtles

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Two kinds of snapping turtles occur in North America, and both of them can be found in Illinois. Alligator snappers, which most people will never see, are listed as endangered, and they inhabit only larger rivers and streams in the southern part of the state, the Mississippi, Ohio and Wabash Rivers, and tributaries directly connected to them. In fact, no wild alligator snapping turtle was documented in Illinois for the thirty years between 1984 and 2014, when scientists from the Illinois Natural History Survey discovered one.

(Ironically, as I reported in a commentary last year, they discovered a wild alligator snapper as they sought to relocate individuals they had translocated from other states as part of a multi-year program to reestablish alligator snapping turtles in Illinois. More on that project here in future.)

It’s only common snapping turtles, scientific name Chelydra serpentina, that residents of Illinois are likely to see, and it’s them I’d like to call attention to here. Common snappers can be found throughout the state, and their overall range includes the entire eastern two-thirds of the U.S. and corresponding parts of southern Canada.

The “common” part of Chelydra serpentina’s name is entirely appropriate. They can be numerous in suitable habitat, and suitable habitat for them includes lakes, ponds, and marshes, as well as rivers and smaller streams—just about any permanent body of water. And while we’re on the topic of names, “serpentina” fits well, too, given the common snapping turtle’s long, snake-like neck and it’s ability to strike in a flash.

[Photos of common snapping turtles by author.]

Humans who wade or swim in waters where snapping turtles live have little reason to fear being bitten by them, because they strongly prefer to avoid us and they move with ease in water.

What do common snapping turtles really want to bite? Fish, of course. Or frogs, or snakes, or crayfish, or snails, or small mammals and waterfowl—really, they’re not picky, and they eat carrion as well as prey they dispatch themselves. Snapping turtles even include a fair amount of plant material in their diet.

On land, snapping turtles respond to humans and other threats more aggressively, since they possess neither speed to escape nor the ability to retreat fully into their shell. But their strength to bite through objects people provoke them with is greater in stories than in reality.

You’re most likely to see snapping turtles on land in June, when females leave the water to find a site with loose soil or sand in which to lay eggs, up to 30 of them. Digging a hole and covering their eggs with soil is the extent of care female snappers provide, so few nests escape predation, and even hatchlings from successful nests face long odds of surviving.

When I see other kinds of turtles on a road I stop to pick them up and move them across in the direction they are headed, but it’s not a good idea to do that with large snappers. Better to give them space and just direct oncoming traffic around them, as long as it’s safe to do so.

Given the right vantage point, it’s also possible during summer to observe snapping turtles as they bask, usually by floating near the surface of the water with just their snout sticking out. In Champaign we’ve got a perfect spot for that, the overlook on the east side of the Second Street Basin. There are no guarantees in wildlife watching, but if you approach the railing there slowly and quietly on a sunny afternoon, you’ve got a good chance of spotting a basking snapper for yourself.

Thursday, June 18, 2015

Mystery of the tiny bouncing spheres

Mystery of the tiny bouncing spheres

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What’s shaped like a ball and white, less than a millimeter in diameter, and bounces like a Mexican jumping bean?

This odd question occurred to my wife, Karen, last week as she locked her bicycle to the rack near her office on the University of Illinois campus in Urbana. She’s not the sort of person who conjures up such questions hypothetically. It occurred to her because the concrete at her feet was alive with such spheres—thousands upon thousands of them—and she had never seen anything of the sort.

Initially, she speculated the bouncing spheres were associated with the many ants that were also present—eggs, maybe, or larvae, and that their movement was caused by the adult ants shifting them from one place to another. Needing to get on with her day, she snapped a photo to share later with others who might be able to shed light on the question.

As it turned out, however, the photo didn’t contain enough evidence to produce a good answer, so she and I returned to the scene for further investigation together a few days later at lunch. And what a scene it was—thousands of white balls bouncing around on the concrete, tiny enough to go unnoticed by most people walking by, but large enough to be seen with the naked eye by anyone curious enough to stop for a look.

We noticed almost immediately that the spheres moved without any help from ants. And by shielding them with our hands, we ascertained they weren’t being propelled by breezes, or just bouncing up from the ground after falling. But they did originate from above. The leaves of the massive bur oak tree standing over the bike lot were covered in them, and they popped off the leaves at a touch.

Thanks to internet access, the solution to our mystery was just a few keystrokes away. We searched “oak tiny white Mexican jumping beans” and that took us to—drumroll—jumping oak galls!

Jumping oak galls form around the larvae of tiny, stingless wasps as they feed on the leaves of certain species of trees in the white oak group. As the larvae mature, the galls fall to the ground, where they overwinter and then emerge as adults the following spring.

Although jumping oak galls have been observed in the U.S. since at least the 1870s, the questions of why and how they jump have yet to be investigated very fully. In a paper published just last summer, researchers from the University of California at Santa Cruz suggest that the jumping behavior protects the gall-wasp larvae from getting too hot and drying out, which can kill them. By jumping repeatedly, they settle down into the leaf litter, where conditions are cooler and moister than above. That’s the “why.”

As for “how,” the researchers observed that the larvae are packed into their galls so tightly it’s impossible for them to cause movement by thrashing around. As an alternative, they propose the larvae move by means of snap-like abdominal contractions, which transfer momentum to the gall shell through the fluid that surrounds them. As far as the researchers know, this mechanism for producing motion is unique to jumping oak gall wasps.

Whatever conclusions scientists eventually come to about how jumping oak galls jump, I am delighted to have found something so new to me and so weird in a spot that’s been part of my everyday experience for nearly 30 years (thanks to my observant spouse, of course). Who knows what we have yet to learn about the 1300 or so other species of gall wasps that occur around the world?

Friday, June 12, 2015

Jumping oak gall video clip

I shot this video of jumping oak galls on the U of I campus in Urbana, under the bur oak tree between the English Building and Lincoln Hall.