“If you would win my heart, sing me a love song.”
~Jane Griner in the song “Sing Me to Heaven” by Daniel E. Gawthrop
Given the title of this blog, you might think it’s going to be about all the riotous birdsong that is happening out in our woods right now as temperatures warm and spring seems to be slinking up the south-facing slope across the road and into our north-facing yard. But that’s not the love song Mike and I heard last weekend when we took our hammocks out to the ravine behind our house (another south-facing slope).
As I was laying in my hammock soaking up the sun like a lizard, I noticed a repetitive sound like two very short, quiet snare drum rolls followed by four to six slower beats that almost sounded like an extra-rapid secondhand on a clock. At first I thought it was just the straps of my hammock rubbing on the tree. But as I paid attention to the rhythm of the hammock’s movement, I realized the timing wasn’t right. I started looking around to try to pinpoint the source, and I noticed a wolf spider moving through the dry leaves on the forest floor. Amazingly, the sounds corresponded exactly to its movements – the snare drum rolls when it was paused, the tick-tock of the clock while it was moving. Whenever the breeze was still, I could hear it… first in one place, then another, and another. At one point, there were three wolf spiders moving around me, all making the same sound sequence. I’d heard that you’re never further than 4 feet from a spider – even while indoors – but it seemed more real as I realized just how many spiders there were surrounding my hammock!
I watched the spiders for a long time trying to figure out just what was going on. Finally, two of them, one after the other, walked right below the edge of my hammock and I got a good view. Whenever they stopped and made the snare drum sound, they were moving their pedipalps (two front appendages, shorter than legs) up and down, vibrating on the dry leaves. It was incredibly fast, but when one of the spiders was close, I could actually see the movement. I was amazed! And as it walked through the leaves, I noticed it tapping its abdomen, which seemed to be producing the tick-tock sound. After that, I was hooked and probably spent more than an hour stalking these spiders with my iPhone, trying to capture their behavior.
I enhanced the volume on this video so that you can clearly hear the sounds the spider is making. I promise it’s the spider and not me shifting around in the leaf litter! But I still wasn’t satisfied that I understood what was going on… so I switched my phone over to slo-mo mode and tried to catch the movement of the spider again…
It’s subtle, and the sound is different because it’s slowed down, but you can definitely see the pedipalps moving as the faster rhythm is played. And you can hear the louder, more separated beats as it taps its abdomen.
Here’s another slow motion video. In this one, you can see how the presence of dry leaves amplifies the sound – when the spider is on the log, there isn’t much sound produced at all. But if you watch closely, you can still see its body vibrating as it makes the sound.
Knowing a little bit about spider mating rituals, I figured that the sounds I was hearing had something to do with that. In fact, just a week ago, on Valentine’s Day, I attended a talk on “spider love” put on the NC Office of Environmental Education. Dr. Eleanor Spicer Rice, author of Dr. Eleanor’s Book of Common Spiders, came to talk about the fascinating stories of spider mating. She was quite funny – her categories for male spiders interested in mating with a (almost always larger) female were: “how not to get eaten” and “well, let’s just make the most of it.” This is because it’s not uncommon for a male spider to be attacked and eaten by a female when he comes seeking something entirely different. For many orb-weaving spider species, the male will pluck the strands of the female’s web in a particular way to indicate that he is a potential mate and not just a fly that’s stuck in the web (aka, dinner). Other species like the green magnolia jumping spider will wave their legs around in something like a dance to show off for a female. A few species know it’s a lost cause and just go for it… and some even die in the act of copulation so as to leave their carcass attached to the female, effectively blocking access for other suitors. The world of spider courtship is dangerous!
Spider sex is fairly complicated as well. The female’s epigynum is located on the bottom of her abdomen, so rather than try to arrange himself upside-down underneath her, males go through a bit of preparation for mating. They produce sperm in their abdomen (from a gonopore about midway down on the bottom side, as you might expect), but they have to transfer it to the specialized “boxing glove” (cymbium) at the end of their pedipalps (via what’s called a sperm web) in order to mate. At least that way he has a chance to keep his many eyes on her chelicerae (jaws) while in the act.
So, back to my drum-playing spiders in the woods… a quick Google search turned up a bunch of articles about the so-called “purring wolf spider” or Gladiclosa gulosa. Apparently, wolf spiders are known for producing vibrations to attract a mate, and most early naturalists thought the sounds were caused by exactly the same thing I did – the spider tapping its pedipalps on a surface like a leaf. But in 1975 a researcher used high speed video to check this out in detail – and it turns out that spiders actually have what’s called a “stridulatory organ” on their pedipalps. Basically, this means that they are able to rub one part of their body against another to create a sound. Other insects are known to do this: the sounds made by grasshoppers and crickets are stridulations, and Mike included information about stridulation in horned passalus beetles in a previous post. But spiders don’t have ears… so it’s long been assumed that the vibrations are what is really important in communicating with a potential mate. However, researchers at the University of Cincinnati have been studying vibration- and sound-making in spiders, and for Gladicosa gulosa they discovered that not only does a female spider respond to the vibration produced by the male, she also responds to the sound (but males only respond to the vibrations).
Most of the studies that I could find describe spider behaviors when males are in the presence of females. And most of those on the sounds of wolf spiders focus on the snare drum rattle of the pedipalps and not the abdomen tapping. No one described the behavior we saw in the woods – namely, that a bunch of spiders were wandering around making sounds without another spider nearby. I’m not sure what was going on, but my assumption is that they were literally trying to drum up a mate!
I’m also not sure what species Mike and I spent time observing in our woods, though I’m fairly certain it is a species of wolf spider (family Lycosidae). I’m not even entirely sure that they were males, because it’s hard to tell in my iPhone pics if the pedipalps have those distinctive “boxing gloves,” though their behavior makes me think they are males. After an exhaustive search of Bugguide.net and the 4 spider field guides in our house (yes, we have 4 spider field guides), I’m still not sure, though it’s possible these are Gladicosa gulosa – please let me know if you can identify them!
Whatever species they are, they exhibit an incredibly fascinating behavior, so if you’re a super nature nerd, it’s time to head out into the woods with a hammock on a warm, still spring day and listen for some spiders!