Friday, August 31, 2012

Yellow Garden Spider

I took one look at you ....and my heart stood still
                                       --------Rogers & Hart

Our friend Georgia sent this picture of a "banana spider" which is seen frequently in her garden, asking for its real name. In a prevalent and distinctive looking spider such as this we run into many common names. Whether you like Latin names or not, they are necessary to confidently identify a species.

This is Argiope aurantia, the Yellow Garden Spider, and based on its size and full rounded abdomen it is most likely a female. Between three different authoritative sources it carries the common names of writing spider, corn spider, black and yellow garden spider, zipper spider, banana spider, x spider, corn spider, the yellow and black garden spider, the black and yellow argiope, the golden orb weaver, and yellow argiope.  This impressive list demonstates the importance of a scientific Latin name.

The distinctive zigzag web vertically through the web is called a stabilimentum. It is common among the Argiope (Ar-gee-O-pee) spiders but is produced by over 80 spider species.  A. aurantia makes an especially thick stabilimentum. It is called a "writing spider" from an old old folk tale that says if you see your name written on its web you are about to die - but hopefully not before you can submit the video to Youtube. So much for the kind and empathetic writing of Charlotte's Web.

The beautiful circular web A. aurantia builds is temporary, as they eat all but the long foundation webbing every night, spinning a new web for the next day. Some sources feel they may do this to add tiny particles to the webbing which look like food to small insects, drawing them to the web.

The zigzag stabilimentum is especially interesting. It is made of a slightly different webbing which reflects UV light, possibly attracting insects to it. It is important to recall that other species frequently see different light waves. Other biologists believe the stabilimentum is made to strengthen the web, confuse predators or to warn birds not to fly into the web. No one has asked the spider.

The story of a female spider eating the male after mating is a familiar one in many species (see Black Widow blog). The Argiope is different- the male effectively commits suicide by sex. Spiders transfer their sperm to females using their specialized palps which the male inserts into the female. In the case Argiopes, they die right after inserting their second palp, their heart stops beating several minutes later.  This gives a whole new meaning to Rogers and Hart's lyric, "...and my heart stood still."

The second palp remains inserted into the female, effectively plugging the opening and preserving the males genes from contamination from another male. In other words, he makes the ultimate sacrifice to preserve his inheritance.*
The male’s death is also described as an “irreversible seizure” and apparently this takes place to form a kind of “chastity belt” (James 2003*). Once the male Kamikaze has inserted the second palp, he’s stuck, despite what the surrounding males would like. "The other males go berserk, bite into the legs and try to pull him off." Securing himself inside of her also gives the male’s sperm sufficient time to fertilize the eggs. **
Meanwhile the female never gets to enjoy her 1000+ kids.  She makes a round brown egg sac, attaches it to the web and watches over it.  The spiderlings hatch but the first instars remain in the sac over winter while she dies.  They emerge in the spring to spread out into new territory.  I wonder it the thought of raising 1000 kids is what kills her?

*    See this NIH publication.
**  Comprehensive A. aurantia information with references is at this link.

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