Saturday, October 27, 2012

The Inexplicable Mojo of Tiger Beetles.

Horn's Tiger Beetle, Cicindelidia hornii Schaupp:
A Rebuttal.

Based on a recent perusal of current literature and various internet sources, it appears that some information concerning the behavior, seasonality, alleged rarity, and color forms of Cicindelidia hornii Schaupp warrant further discussion. Apparently, a great deal of this information and supposition is based upon brief incidental field collections - or lack of - and observations. For most, this species is a fortuitous hit-or-miss opportunity - a collateral species. As a result, it carries an exaggerated distinction as being a rare and highly coveted species.

Typical habitat of Cicindelidia hornii Schaupp
Upper Sonoran Mesquite-Grassland
Sulphur Springs Valley, Cochise County, Arizona
Alleged rarity. 
I see the term rare so commonly used in entomology, that in fact, it has lost it's connotation. One must remember that when dealing with things biological - anything is possible. Consider that beetles, and insects in general, emerge and become active when a certain combination of physiological and environmental stimuli are reached (moisture, temperature, humidity, for example) indicative of phenotypic plasticity: any change in an organism’s characteristics in response to an environmental signal (Schlichting and Smith 2002:190).

In southwestern North America, moisture, in the form of winter rain or summer monsoons, is an essential factor in this equation. Without this necessary moisture insects may delay their emergence for several months or years. I have collected "early" Pleocoma species (australis, fimbriata, marquai, puncticollis, and tulerensis) that, in typical winters emerge in September through December, as late as March in years when precipitation was late or scant. I have also noted similar delayed Pleocoma activity during exceptionally cold winters. My point being, there are prevailing factors that influence, or deter, fecundity (abundance), of an organism - despite the exhortations of frustrated collectors.

Another habitat photo of Cicindelidia hornii Schaupp
Upper Sonoran Mesquite-Grassland
Sulphur Springs Valley, Cochise County, Arizona
Behavior & Seasonality. 
In southeast Arizona, C. hornii emerges during the summer monsoon that typical begins in late June or early July. It is best described as an ephemeral species because it is active while the soil remains damp after rainfall. Once this moisture evaporates, it disappears along with other sympatric species, such as Cicindela pulchra dorothea Rumpp (below, left). In the field, it typically occurs in grassy pastures and roadsides where it will hide in the shade beneath grass clumps during mid-day hours or seen running in between these clumps in search of prey.




Cicindela pulchra dorothea Rumpp
Polymorphism: Color Variation.
Polymorphism is the occurrence of more than one color form, or morph, in the same population of a species. Of the various publications and websites that display images of C. hornii, usually only one or two color forms are illustrated. Based on specimens in my collection, iridescent metallic blue, blue-green head and pronota with purple elytra, blue-green to green, and black are represented. The latter melanistic form being the most commonly encountered in the field. Although anecdotal, from my field observations, it appears that the more brilliantly colored individuals appear earlier in the season. Victor E. Shelford, in his treatise, Color and color-pattern mechanism of Tiger Beetles (1917), noted that tiger beetle coloration was influenced, in part, by climatic conditions.

Color variation of Cicindelidia hornii Schaupp:
blue, bluegreen head & pronota with purple elytra, bluegreen-green, black.

Literature Cited

Schlichting, C. D., and H. Smith. 2002. Phenotypic plasticity: linking molecular mechanisms with evolutionary outcomes. Evolutionary Ecology 16:189–211

Shelford, V. E. 1917. Color and color-pattern mechanism of tiger beetles, with twenty-nine black and three colored plates.Volume Illinois Biological Monographs Vol.3: No. 4

                                                          Other Suggested Reading

Schultz, T.D., and N. F. Hadley. 1987. Structural Colors of Tiger Beetles and Their Role in Heat Transfer through the Integument. Physiological Zoology. 60 (6):737-745

                                           © Delbert La Rue 2012. All Rights Reserved.       

7 comments:

  1. I'm glad you are writing again Delbert - very interesting! I got down to Fred's one day late a few years ago. The day before everyone collected a good number of C hornii but there were none out the next day when I arrived. Ephemeral! That is a perfect description. I did trade Charlie O'Brien for a couple - a black and a purple specimen. So I have them in my collection, and have hunted in their habitat for them - a day late... Perhaps one day I can be at the right place at the right time!

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  2. Thanks, Paul,

    I just noticed your comment.

    As I mentioned in the post, the hornii are out while the soil is still damp which non-cicindelid collectors don't realize. Hence, the presumption that they must be rare. At the right time after the monsoons begin, they are dirt common.

    Best wishes and thanks for your continued interest.

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  3. The "Alleged rarity" part is a great point. I went out a few weeks ago looking for Pleocoma in the north/central western Sierra Nevada. One week previous to this, there was a slight sprinkle, but the weekend when I went out there were on and off down pours throught the weekend. I was certain that I'd catch tons of Pleocoma, but I didn't catch a one dispite black lighting and checking lights around various parts throughout the mountain range the whole night. This was discouraging, but then again makes me appreciate some of the beetles I have in my collection that I may never have the luck to catch again.

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  4. May I offer one word toward your Pleocoma efforts? Persistence.

    Keep checking your localities. Not getting them is no reflection of your skills or lack of knowledge. They are notorious for not flying when things are "perfect."

    Let me know if I can be of further assistance.

    Thank you for your continued interest and comment(s).

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  5. I have just got one thing to say. If you don't go, you don't get them! You know what I am talking about boy.

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    Replies
    1. "That's the problem with you California boys, always trying to get outta work. Sh*t boy!"

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  6. I just have one thing to say. If you don't go, you don't get them. You know what I mean boy!

    ReplyDelete