Tuesday, May 12, 2009

Webspinners


One of the most fascinating and unique insects to be found here in Tucson is the “webspinner.” They even have their own order, the Embiidina (formerly Embioptera). Adult males like the one pictured above are drawn to lights at night, and at under 10 mm, they are easily mistaken for alate (winged) termites.

I first became aware of webspinners because one of my childhood idols, insect photographer extraordinaire Edward S. Ross was also the world authority on these obscure insects. He still is the expert on embiids, in fact. Discovering new species of webspinners took Dr. Ross all over the globe, as the diversity in this order is mostly tropical. During his expeditions, Ross also took amazing images of other insect species, many of which graced the pages of National Geographic magazine.

Nearly everything about webspinners is bizarre. They go through a simple metamorphosis, with immature individuals resembling adults, but the females never develop wings. Most species are live in galleries of silken tubes under loose bark and stones, or leaf litter, often in a matriarchal congregation of a parent female and her offspring. The insects can move quickly through their silken tunnels, usually moving backwards. The wings of adult males flip forward so they don’t catch on the silken walls during backwards maneuvers.

Perhaps the oddest feature of their anatomy are the front legs. The swollen “feet” (tarsal segments) contain the glands from which the silk is spun. This appearance of having ankle weights or Popeye forearms easily separates webspinners from winged termites, small stoneflies, and other look-alikes. Even the youngest web-spinner can do just that: spin silk.

Webspinners feed mostly, if not exclusively, on decaying vegetable matter, though adult males do not feed at all. The mandibles (jaws) of males are modified for chewing holes in the galleries of females, and for grasping the woman of his dreams during courtship.

Three families of webspinners are known to occur in the southern United States, with one species reaching as far north as southern Oregon. Our common Tucson species is Oligotoma nigra, but it is not native, having come traveled in date palm cuttings from Egypt and the Persian Gulf sometime in the 1800s. It is believed that India is the true place of origin for this insect. Now it is widespread in the tropics, and ranges from San Antonio to southern California, and north to Utah in the U.S. There is also a documented record from Arkansas.

For more information on these amazing invertebrates, I recommend the World Wide Webspinners website, recently constructed.

14 comments:

  1. Ah, one of my favorites too!

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  2. Faskinating. I'll be looking for them from now on.

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  3. Very cool -- great blog, Eric!

    Keep an eye out for Sclerogibbid wasps which parasitize these guys (Probethylus schwarzi is in AZ).

    -George

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  4. I am having these pop up in my room at night.

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  5. We have them in our house in Ohio, how do we get rid of them??? They have made their way into my daughters bed and some times crawl on us while sitting on the couch!

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    1. First, webspinners do NOT occur that far north (not unless you brought furniture from a very southern region of the U.S. to Ohio). Second, I NEVER respond to "how do I get rid of..." questions. Webspinners are not even pests.

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  6. @bug Eric if you found any way to get rid of web spinner please let me know.

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    1. I *never* give advice on how to "get rid of" any organism. Also, there are many other harmless insects that spin webbing. Some barklice (Psocodea), for example. Then there are spider mites that spin silk, and that *can* be pests....

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  7. I keep finding these in my bathroom. I live in Texas. Should I be concerned? I thought they were termites at first until I did some image searching and research

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  8. They are cute but a pest nonetheless. It would be nice to know how the got in my home.

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  9. I live in Tucson and I adore these little bugs. They hang out in my the middle of my papers when I'm working late at night. When they come visit, I carefully work around them so as to not disturb or hurt them. They seem to have sweet friendly personalities - yes, personalities! I am not a crazy person :)

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    1. You are not crazy. I also work around them, while watching out for their safety. I also capture them and remove them to the outside.

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  10. I have been sporadically finding these in my bathroom and kitchen in central to Northern California. I freaked out and thought they were termites but their wings are darker and they look just like the pictures. Such a relief to know they are harmless.

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