Spider mating habits can repair ignorant slanders against Darwin

I don’t know about this Salon article, “A microscopic evolutionary arms race is happening between sperm”. It’s OK, but it put me off in the introduction.

As world-enlightening as Darwin’s ideas of natural and sexual selection were, there’s a tiny whiff of failure about him as a scientist. Brilliant as he was, he never realized that natural selection and sexual selection aren’t quite enough to explain evolution.

That’s just wrong. He didn’t get everything right, and he certainly didn’t explain everything about evolution, but he was humbly self-aware of that fact. There is no “tiny whiff of failure” associated with a scientist failing to explain the totality of evolution. If that were the case, every scientist ever would reek of failure. That passage reads more like the author is surprised by new discoveries in the field, and is projecting her own disappointment that a single book from 1859 was not comprehensive.

Also, nothing in the article is a new discovery. Sperm competition has been a known phenomenon for at least as long as I’ve been a biologist. There was a long-running aversion to the whole concept of polyandry, thanks to Darwin’s Victorian heritage, and I’m sure you can find some old relics in universities somewhere who want to think that sexual selection is all about brawny masculinity battering any competition into submission, but that’s just not the way most species work.

The author redeems herself at least in part by discussing spiders.

Perhaps because they’re easy to catch and breed, much of the research about sperm competition has been done on spiders. February 2022 work from biologists at Ludwig Maximilian University in Munich and Aarhus University in Denmark shows the benefit to mating males of long copulations. When a male nursery web spider (species Pisaura mirabilis, found all over Europe) offers a female a “nuptial gift” of a silk-wrapped bug, she allows him to copulate. What’s more, she lets him continue to flood her receptacle with sperm for as long as the proffered meal lasts. In an email, co-investigator Dr. Cristine Tuni explained the logic of this adaptation. The spider’s ejaculate doesn’t arrive as a brief, happy burst and then stop. Rather: “In this species, sperm is transferred continuously over time from his copulatory organ into hers,” Tuni says. “So, the longer a male has his organ coupled to a female organ, the more sperm is transferred. The relationship is basically linear.”

One egg sac can carry hundreds of eggs. Because of this, any male wanting a big bang for his f**k probably intuits that size (of the gift) matters. Pumping as much semen as possible can help send his DNA on its way.

Malabar spiders
The Malabar spider (Nephilengys malabarensis, found in Asian rain forests) wields a far more dramatic sperm competition adaptation. Each male has two genital appendages extending from behind the mouth. As semen pulsates out of one, the spider detaches it and leaves it inside the female’s receptacle. Even severed like that, the genital continues to ejaculate. Meanwhile, it also plugs the receptacle, making it difficult for another male to get a genital in. Ready to fend off anyone who tries, the mating male stays on the web near the female. Unfortunately for him, each female’s semen receptacle has two openings. He has only plugged one. This means that, if a rival approaches, the mating male will have to fight fiercely to keep him at bay. To that end, and while ejaculation from the abandoned genital continues, many males eat their only remaining genital.

Of course, that seems like a counter-intuitive strategy. Why get hungry at that very moment? Why hurt yourself right when you may need all the energy you can muster?

A team of biologists from several institutions in Europe and Asia seem to have an answer. They compared the battle survival rates of spiders who’d severed one genital to those of spiders who’d severed one and eaten the other. Additionally, they tested the battle survival rates of genitally intact males. The name of the team’s paper — “Eunuchs Are Better Fighters” — says a lot about why, under duress, a Malabar spider would eat its only remaining genital.

But what a way to go.

Unfortunately, it doesn’t discuss one of my favorite peculiar spider mating habits. Dark fishing spider (a common species in my area) males, once they succeed in mating to the point where they’ve inserted one palp into the female’s epigyne, spontaneously and abruptly drop dead. The palp is locked in place and the corpse continues to dribble sperm, but the poor guy is totally deceased, and eventually the female will notice the small dead male’s body dangling from her genitals and eat him.

Remember those horrible 80s comedies that were obsessed with teenagers desperate to lose their virginity? I like to imagine the obnoxious male protagonists having all the sexual properties of Dolomedes.

We got legs!

I am excited to report that the latest generation of spiders in the colony is developing nicely. Here’s a closeup of a Steatoda triangulosa egg sac, and you can see the adorable little spiderling embryos inside. There are legs! Eight of them! Everything is looking good.

A lot of you don’t like spider photos (cute baby spiders don’t count, right?), but you can see those on Patreon. She’s out of focus in this one, but as soon as I put the optics on that egg sac, she scurried over and maternally embraced it — she’s the loving darkness lurking in the deep blur behind the eggs you see here.

How a spider eats

This video has been online for 9 years, and only has 358 views. That’s sad. Maybe it has something to do with the subject?

If you’ve wondered how spiders eat, they have a pair of chelicerae in front of their face that are used for injecting venom/chopping up prey, but they’re not for ingestion at all. They have mouthparts behind the chelicerae, which they then use for sucking up fluids and spitting up more saliva. The video is a closeup of a prey animal with a rather translucent exoskeleton, so you can actually see the juices sloshing around inside and being sucked out. This is cool; fruit flies don’t show much, there is only a small amount of bug goo inside, but I have seen mealworms get their guts literally drained out of the exoskeleton, leaving nothing but a hollow shell when the spider is done.

I can guess why this is an unpopular video, so I’ll hide it below the fold.

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Yay! Egg sac!

If you’re on my Patreon, you already knew about my little catastrophe: one of my Steatoda triangulosa had produced a beautiful fluffy egg sac, I’d rewarded her by feeding her a mealworm, and in the ensuing struggle, the eggs had been smashed. Mama Triangulate Combfoot had her vengeance, and sucked that mealworm dry, reducing it to an empty husk. But the eggs were demolished.

Well now she’s gone ahead and produced a brand new egg sac. Look at it, it’s beautiful.

These look very different than Parasteatoda egg sacs, which are finished off with a light brown leathery casing, but they’re both the same otherwise — a nice wooly blanket of spider silk suspends and cushions the eggs inside. Now begins the pregnancy watch, with hatching expected probably next week sometime.

The Great Spider Heist

One of my colleague has a lovely compost bin in their back yard. Or should I say, “had”. They’re leaving our fair campus for a new job in the big city of Madison, which caused me some worry — not just for losing a good contributor in the science & math division, but because, as I’ve reported before, their compost bin has a magnificent colony of Steatoda borealis thriving inside it. Nobody ever asks, “what about the spiders?” when they leave.
So Mary and I…ummm…”appropriated” the compost bin. Don’t worry, I asked permission first, and it has now been relocated to our yard. Just outside our door, where I can check on them regularly.
Is it not beautiful?

It was a disruptive process for many of the spiders. The bottom is open, so hoisting it up meant losing much of the compost inside, but we shoveled up much of it and restocked the bin. No doubt we lost some spiders in the move, but they mainly live in the tangle of webbing inside the lid, not in the compost itself. Lots of egg sacs were still there.

And of course, many agitated spiders scurrying about on the lid.

They live on the small insects that emerge from the decaying compost, and survive the winter on the warmth of the fermenting organic matter, so I threw in some old potatoes I’d been saving for this occasion. We’ll also be much more careful to toss food waste in there, to keep the spiders happy.
We’ll also rename the bin the Atkinson Home for Hungry Spiders, in honor of my colleague.
Although, I don’t understand why he didn’t want to pack up such a gorgeous box full of joy to bring to his new home.

This story has also been posted to Patreon, and I’ll post occasional updates on the status of the happy spider family there.

Spider battles a wasp!

I know a lot of people here dislike spider photos, but this is a video, and it’s a battle between a handsome Steatoda and a much larger wasp. Usually wasps win these kinds of fight, but not in this case, which made me happy.

Also, watch the spider pause once the wasp is lethally envenomated, step towards the camera, and preen for a bit before going back to hog-tie the beast. Bravo!

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The spidering resumes!

We explored the local horticulture garden for spiders and found a few — a lovely young Dolomedes and a rather grumpy looking Philodromus. I try to avoid posting spider photos here, so you’ll have to check out my Patreon or Instagram to see them. Sorry. In recompense, here’s a fly:

I have to ask…so many people are arachnophobic and reflexively avert their eyes at spiders, but do you have the same reaction to close-ups of flies? You know, flies are likely responsible for far more disease and death than spiders, and don’t get me started on their Dipteran cousins, the mosquitoes.

Also, I looked at my Instagram, and it’s just jam-packed with exciting spider photos. Then I looked at the Instagram pages of my more popular, attractive, and charming friends, like David Gorski and Rebecca Watson, and what do I see? Puppies. Lots of puppies.

Am I doing something wrong?

Jumping spiders are peeping toms!

I was first introduced to the wonders of spiders in 1980, when I took a course in sensory physiology from Mike Land, who, if you know his work, is a world-class expert in eyes and vision and optics and comparative physiology. We mainly worked on jumping spiders in that lab because you could just walk outside in the Oregon spring and catch lots of them on the walls of the science buildings.

One of the cool things we learned is that jumping spiders have unusual eye anatomy. Their eyes aren’t spherical, they’re tube-shaped, and they actually function like a Galilean telescope. That’s right, jumping spiders are looking at you through a telescope — they can see things far away relatively clearly. These spiders can look up and see the stars.

We did various experiments on spider vision back then, but one thing we lacked was a spider with a transparent carapace, so we did everything with indirect behavioral and optical methods. This little video would have blown our minds.

We dissected a few spiders and could clearly see the tube-like structure, but that didn’t communicate the dynamic activity of those little telescope eyes at all.