This post is all about sex.

Did I get your attention?

That’s right sex.

Specifically, spider sex.

Wait! Where are you going!? I promise you this will be interesting. And yeah, OK, maybe a little creepy too… especially if you have a bit of arachnophobia. But sometimes full immersion is the best way to get over a phobia, and we’re about to get more immersed in the world of spiders than most people ever dare.

Let me start by introducing you to the female Filmy Dome Spider that is currently living in a bush about 35 feet from my front door. As her common name suggests, the spider has built an impressive dome-shaped web in said bush as seen in the following photo.

If you look closely in the above photo you can see the spider sitting upside down under her dome. In case you are having trouble seeing her, here’s a closer look.

The Filmy Dome Spider’s web is not very sticky, so flying insects usually just bounce off of it. That’s where the domed shape of the web comes into play. Insects flying up from below hit the dome and bounce, but continue to try to fly upward. They keep bouncing along the underside of the dome giving the spider all the time she needs to run over and grab them.

In many common spider species there is an almost comical size disparity between the sexes. Males trying to court females that are 10 times their mass sometimes end up as a meal rather than a mate. I’ve watched tiny male European Cross Spiders carefully strumming away on the threads at the edge of a potential mate’s web trying desperately to play just the right note so she recognizes him as a suitor rather than supper. This often ends with the female making a quick lunge in the male’s direction at which point he bails out and swings away on safety line he had prepared for just this contingency. Honestly, a male spider swinging for his life is the best impression of Spiderman I’ve ever seen an actual spider perform.

In Filmy Dome Spiders, the sexes are of roughly equal size. I assume this size equality is at least part of the reason I’ve never seen a male of this species do a Spiderman impression. They seem to approach potential mates with a bit more confidence that they aren’t about to die in the name of love.

The following photo shows both a male and female Filmy Dome Spider. You can recognize the male by his slimmer, redder abdomen. The female has a plumper abdomen with a more marbled appearance. Both spiders are upside down if you couldn’t tell. That’s how they spend most of their time though, so perhaps for them this is right side up.

In case you didn’t realize it, the two spiders you just looked at were having sex. I know, I know… it certainly didn’t look like sex, but trust me, it was. Let me explain…

This is going to sound strange, but spider sex is kind of like a naturally evolved form of artificial insemination. Both male and female spiders have what look like a tiny, extra pair of legs called “pedipalps”. These are located on the sides of what I guess you would call their face. The male’s pedipalps have highly specialized organs called “hematadocha” on their tips. In the Filmy Dome Spider these almost look like a little pair of boxing gloves, which will seem even weirder once I tell you what they are for. Before we get to that though. Take a look at the following photo. You can see the male on the left holding up his pedipalps with arrows pointing to the hematadocha on the tips. The female is on the right and I have pointed out her genital opening, the epigynum. This will be important later.

If you just had this photo to go by, the little male spider holding up his boxing gloves apparently preparing to punch a very sensitive part of the female’s anatomy, you’d think male Filmy Dome Spiders would get killed and eaten by their mates more often. But what the female spider knows is that before this gentleman came calling he spent a little alone time making a tiny, specialized bit of web into which he deposited his sperm. He then used the hematadocha at the end of each of his pedipalps to draw up and store that sperm. During mating the male presses his hematadocha up against the female’s epigynum and… you know what? You might just have to see this for yourself rather than have me explain it. Look at the photo below to see what happens next.

Yeah. It just got weirder. The hematadocha has this little inflatable bladder on it that flares out like a balloon. It then contracts to inject the stored sperm into the female’s genital opening. You can see this process of inflation and contraction in the animation below. The happy couple were on a web that was blowing in the wind, so that added a little more drama to the interlude.

Once it has been transferred, the female spider stores the sperm within her body until she needs it to fertilize her eggs. Filmy Dome Spiders are not monogamous so the female will pair with additional mates if she chooses to and the male will go reload his boxing gloves and seek additional mates as well.

So there you have it. Everything you never wanted to know about spider sex and more. If you came into this with a spider phobia and you are reading this sentence, congratulations on facing your fears! If you didn’t come into this with a pre-existing phobia but have developed one after reading this… my deepest apologies. :-)