The Other Side of Range Extensions

by Carl Strang

The aspect of singing insect studies that has been of greatest general interest, and about which I have presented talks most frequently, is range extensions. Most of the several examples uncovered so far have been northward extensions of species ranges, and it is easy to jump to the conclusion that this is a product of global climate change.

The first species I found well north of where it previously had been known was the broad-winged tree cricket.

The first species I found well north of where it previously had been known was the broad-winged tree cricket.

If climate is the primary influence in these range extensions, we would expect the southern boundary of a species’ range to shift north as well. However, sticking with the example of the broad-winged tree cricket, its range has expanded south as well as north. I know that only because Tom Walker, the authority responsible for the Singing Insects of North America website, informed me that he has found them spreading down into parts of Florida where they had not been before.

Documenting an expansion northward is easier than demonstrating a disappearance in the south portion of a species’ range. It is easier to prove a positive than a negative. Also, when one has limited time and financial resources, it is not possible to travel south and conduct the necessary regional surveys. So, what to do?

The best idea I have had so far is to identify species whose southern range boundaries occur in my region, and make a point of documenting their presence and estimating their abundance from year to year. There are four best candidates.

The dog day cicada Tibicen canicularis has the northernmost southern range boundary. It is mapped down into the very northern edges of Indiana and Illinois, but I have found it a little farther south, at Braidwood Dunes in Will County, Illinois, and in southern Marshall County, Indiana. My notes suggest that its numbers may vary considerably from year to year in the latter location.

Dog day cicada

Dog day cicada

The broad-winged bush katydid Scudderia pistillata is mapped a little farther south, but I have found it infrequent in DuPage County, Illinois, and its season of activity seems to conclude sooner here than it does farther north. So far my surveys have turned it up in Lake County, Illinois, as well, but not farther south.

Broad-winged bush katydid

Broad-winged bush katydid

The striped ground cricket and sword-bearing conehead are abundant in the region. Their southern range boundaries are mapped about half a state south, but that is the same distance as a number of the northern range shifts I have observed. If entire ranges are shifting, one would expect them to be more scarce.

Sword-bearing conehead

Sword-bearing conehead

This is yet another topic of interest I am keeping in mind while surveying the region’s singing insect species.

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5 Comments

  1. Lisa Rainsong said,

    July 26, 2013 at 7:18 am

    Thank you for discussing this. I’ve been pondering it quite a bit in the past couple of years. I imagine it would take several years to get a better sense of the Broad-winged Bush Katydid’s status in my area (NE Ohio). It is definitely the earliest Scudderia here and it always disappears early. However, it has been much less common in the past couple of years. Is this a trend or a result of last year’s extreme heat and drought and this year’s heavy rains and repeated storms? I don’t know.

    • natureinquiries said,

      July 27, 2013 at 7:20 am

      A few years ago I was surprised to find them singing in the UP of Michigan much later in the season than they are active here. A confounding factor is that here, they share habitat with Texas bush katydids, which are absent up there.

  2. August 5, 2013 at 6:26 am

    […] good numbers of broad-winged bush katydids and a couple dog day cicadas, two of the species I am following for southern range boundaries. The dominant singer was the lyric cicada, with loud choruses providing a continuous background […]

  3. AlStoops said,

    September 7, 2014 at 9:59 am

    I found your site while searching online for a question I have about the Sword-bearing conehead. I live in southwestern New Hampshire, and most years theirs is the most prominent insect call of late summer in this area, but this year I have heard very few. I suspect it’s just a normal population fluctuation, but I’m curious what’s causing it.
    I lived in Ely, Minnesota (northeastern part of the state) for awhile, was there summers 2008-2010, and didn’t hear any until the last year I was there, despite listening for them. (Online maps show Ely to be near the northern edge of its known range.) For years before that I was in the same area here in New Hampshire, and heard them every summer since I’d learned about them—-also heard them once near Cleveland (Elyria) Ohio.

    • natureinquiries said,

      September 9, 2014 at 5:53 am

      Hi, Al, thanks for the information. Fluctuations in insect populations are, as you say, normal. Sometimes they correlate with weather conditions, sometimes with parasites. Male coneheads are subject to parasitic infections by specialist fly species that home in on their songs, and that is one potential cause. The reduced host numbers should collapse the parasite population and set the stage for a renewed growth of the coneheads.


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