Naturespeak A naturalist's view of the world

August 6, 2011

She with Spines Upon Her Rear

Filed under: Uncategorized — wykes @ 11:32 am

This makes the third blog in a row which either features or involves a spider of some sort but, dog-gone it, I just can’t ignore these things (even when they force me to eat some crow). On a recent evening walk with some friends, I came upon a splendid little gem of an arachnid called a Spined Micrathena. This individual was suspended upside down in the center of her finely made little orb web. In spite of the evidence to the contrary (in the form of a half dozen tiny midge corpses hung upon it) I reasoned that this web must have been freshly made. Most spiders make fresh webs at night and the hour was late, so I lapsed into lazy spider logic and claimed that “she will eat her web in the morning and spin a new one the following night.” Unfortunately, I had that part bass akwards. In the case of this species, they spin their webs anew at dawn and take them in at night – not the other way around.

I am glad to admit to this crow-eating event because it makes for one less mistake in the future (at this rate I will be perfect by the time I am 156 ½ years old!). My later research on the topic showed conclusively that Spiny Micrathenas are daytime hunters. They like flies. Although their circular orbs are quite small and finely made, they are centered between lengthy support lines (usually two parallel lines) that may span over 6 feet from end to end. They are known for extending these stout lines across trails and bridging the wide spaces available in open deciduous woodlots. This is why early morning trailwalkers should carry long sticks (and speak softly lest they ingest one of the spiny makers). They often leave these tie lines in place while renewing their orbs, so they can remain in position for up to a week in the absence of blundering humans or deer.

All this website stuff is fine and good, but the spider herself – the web surfer- is alone worth the price of admission.  My use of the term “she,” by the way, is due to the fact that the males do not make webs. The males of this species have small un-adorned bottoms and slink about in the underbrush hoping to connect with “she who has spines upon her rear.” It is the magnificently spined rear on the female that is her claim to visual fame.

When disturbed, these spiders will leave the orb and retreat to the cover of nearby vegetation via one of the main support lines. I caught my spider in the act of retreat – hanging upside down like a monkey on a tightrope (note the differing structure of each set of legs – they are not all of equal length). In this position, the five pairs of defensive spikes adorning the abdomen are well displayed. The structure is hard, so these spikes would be formidable barriers for hungry birds. It is also possible that because it resembles a seed, bug-eating birds may be fooled by the appearance.

Perhaps the most remarkable thing about these spiders is their ability to make sound. A number of spiders in the Argiope family, such as the Spined Micrathena, are capable of making a buzzing sound if appropriately ticked off. By rubbing a set of stiff hairs on the inner side of the back set of legs onto a ridged structure located on the inner abdomen, they can generate a low-pitched buzz. The sound plates, located on the so-called book lung covers, look like three dimensional fingerprints, but are is too small to see in my detail photo.

Unfortunately, I did not hear my spider speak, angrily or otherwise, on my evening stroll. I therefore challenge you to bring your ear close to the next one you encounter and you’ll likely hear it buzz just before it enters your ear. Go ahead, try it and let me know how it, sounds.



1 Comment »

  1. Ah, bustle-butts! I love spined micrathenas and they are often my go-to spider when leading hikes. I was unaware they could make sound. Now I must go out and appropriately tick off one. Thanks for the tidbit 🙂

    Comment by swamp4me — August 6, 2011 @ 1:54 pm

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