Be My Valentine: Male and Female Garden Spiders

Sexually dimorphic garden spiders oppose each other on a web (Araneidae: Argiope). (Photo by Jessica Hyde)

For Valentine’s Day we have garden spiders.  These are the big spiders you find with the zig-zag patterns in their webs.  It turns out their mating habits are even more entertaining than I had thought (journal articles are fun!).

The much smaller males build mini-webs in at the edges of the females’ webs, often complete with their own tiny zig-zag.  Then the male commences a careful and prolonged courtship, plucking and vibrating the strands of the female’s web to play her a love song.  He’s trying desperately to convince her to mate with him before she decides to eat him.  In this case, his small size is an advantage.  His lady love may ignore him because he’s of little nutritional value.

Like other spiders, the male uses his pedipalps to transfer sperm.  This is the part where a previously quiescent female may turn vicious–a quarter of males are killed during the first insertion attempt.  The little male is hoping to manage one insertion with each pedipalp, as surviving through two insertions uneaten will increase the number of eggs he fertilizes.

After that, his lover’s appetite will become a moot point:  during the second insertion the male will spontaneously suffer a fatal seizure.   Although this could be interpreted as a romantic sacrificial gesture (box of chocolates, anyone?) it is more likely he is using his body as a plug, to try to block the access of other males.

Be mine, Valentine?

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Thanks to Jessica, who took the picture for me after I ran around the ranch house squeaking about dimorphism and catching grasshoppers to toss to the spiders.  Thanks also to the spiders, who caught me a gorgeous buprestid specimen which I stole and unwrapped.

(Elgar 1991; Foellmer 2004; Hickey & Lee 2004)

Exponential Orbweaver

A gregarious orbweaver in Argentina.

Another arachnid post.  These spiders were one of the most striking arthropods we encountered in Argentina.  The females of these colorful spiders are nearly palm sized.  Communities of these gregarious or sub-social spiders form their webs in large groups, thus filling a small area with many, many huge spiders.  This lead to some interesting encounters.  Myrmecologists scouring the ground for fire ant nests aren’t always particularly aware of, say, what might be going on with spiderwebs in the trees they’re walking through.

An aggregation of gregarious orbweavers in Argentina

It is very disconcerting for the spider-wary to accidentally stumble into one of these clusters of giant spiders.  Luckily, I did not find them to be particularly aggressive.  The webs are sturdy, however, and capable of straining fairly large flying prey from the air.  We even saw a bird become trapped in one of these webs for several minutes before it beat its way free.

A bird caught in the web of gregarious orbweavers (photo by Dr. Shawn Wilder).

In truth, I haven’t been able to find out much about these spiders.  Does anybody know of any good references?