I mentioned a while back that we had this surplus of spiderlings and that we were going to do some measurements of survival under different population densities. Well, we’ve got two weeks of data now, so we can think a bit.

It was a simple experiment: we put different numbers of recently emerged spiderlings in two different sized containers. We had 5, 10, 15, or 20 spiders in containers that were either about 100ml in volume, or 5.7 liters, so spider density ranged from 0.0009 spiders/ml for the big, nearly empty containers to 0.17 spiders/ml in the small overcrowded ones. We’re basically asking how crowded to they need to be to start affecting each other’s survival, and what’s the greatest density we can get away with, anticipating that no matter what, some will die. And the answer is…

Density doesn’t matter. It didn’t matter how many spiders we started with, or whether it was a small or large container, we ended up with 1-3 spiders in a container at the end of two weeks. You start with 10 in a giant container, you end up with about 3; you start with 20 in a tiny box, you end up with about 3. They’re all spaced out, too; we found that individuals tended to occupy different corners, no matter how much room they had. There were no containers which had 100% mortality.

What does that look like? They seem to be murdering their siblings to set up exclusive territories. Ah, the life of an adolescent spider. What it means is that only about 20% of the spiderlings have survived this battle royale so far. Maybe eventually they’ll be reduced to one spider per container.

Dang. Next experiment is to set up containers for individual spiderlings to see if that increases the overall survival rate. If it does, then I’ve got to do some more thinking. I can’t possibly accommodate every spiderling produced by a parent, since that would mean I’d have 150ⁿ spiders in n generations, with a generation time of about a month, so in a year I’d have 10²⁶ spiders, which would mean I’d have to pack about 10¹² spiders per square meter of Earth’s surface area, and I’d have to take over the earth to provide housing for my brood. Oh, man, and all the flies I’d have to raise! Sorry, everyone, I’m going to have to draft everyone on the planet to help maintain my spider colony.

Alternatively, I have two more modest strategies. A) I handpick the small number of spider babies I need to repopulate my colony and maintain the population size, which would require raising their offspring in individual containers. Or B) I put a small number, say 10, spiderlings in small containers, expecting that most will die in a vicious battle royale, and only one can survive in each container. There can be only one! But that one will be the most savage, ruthless spider of the group. It’s mollycoddling vs. natural selection.

Maybe I can do both for a while and see which strategy leads to the healthiest next generation.

One worry is that (B) might lead to the total extinction of all males, since the females are bigger. In nature they can disperse far apart, so we don’t have as much fratricide/sororocide, other factors will cull them. Get males from population A, and females from B? This sounds like another experiment.

Yesterday, we let Iliana play in a cardboard box. But before we could do that, we had to clear out the spiders that had rapidly colonized it first, and that’s how we caught this nice Parasteatoda. Last night, while we slept, she spun an egg case and laid a lot of eggs in it, and then today, I had to put her in a different container. She would not go. I tried every trick in the book to separate her from her egg case, and she would frantically scurry back up into the vial. Then I tried removing the egg case; no go. She had it tethered, and as soon as I got it away, thwip, she’d reel it back up. I had to give up and let her stay with her eggs. These spiders are extraordinarily maternal.

Nope, I’m not going to battle that to get her treasure. My party is going to have to level up a lot more.

I’ve got one baby at home, and today when I came in to the lab we found even more babies…cute little spider babies. It seems this was the weekend almost everyone decided it was time to emerge from the egg sac, and seven egg sacs spewed out clouds of spiderlings.

This is a little overwhelming. I spent a few hours separating out spiderlings and trying to spread out the masses to more containers.

Here is the maternity ward. See all those vials with foam plugs? Each one contains a female spider and one or more egg sacs. If you look closely, you can see lots of little dots, and that’s the cloud of new babies. That’s probably a thousand spiders you’re looking at.

Let’s zoom in a little on one of the vials.

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They’d be sending palp pics.

Swipe left or swipe right?

I was not looking forward to today — we have these swarms of spiders hatching out, and we have to do something with them all. They’re in cramped little petri dishes, an entire clutch together, which is fine early on, since they naturally aggregate after first emerging from the egg sac, and then a few days later start ballooning and dispersing by wafting away on the wind. “Wafting away on the wind” isn’t a great strategy for maintaining a laboratory colony, though. Last year I would pluck them out one by one and put them in tiny individual containers, which is ridiculously labor intensive, and then feed them flies individually, even worse, and that wasn’t going to work at all with the numbers we’re dealing with. Especially since fall term starts way too soon, and students are going to be occupied with mere classes.

So my student Maya is doing a simple experiment to see the effects of population density on juvenile mortality. We didn’t put the spiderlings in individual containers, but in two different sizes of containers in different numbers. We opened up the petri dishes of spiderlings and counted out individuals into larger containers.

It was amusing and different. The spiders, as soon as the lid was off, saw freedom awaiting them and would put out a thread to start ballooning. We’d gently sweep in with a paintbrush and snag them, move the brush over their new container, and give a little shake — sometimes they’d oblige by neatly rappelling down, sometimes they’d jump off, sometimes they’d get obstinate and you’d have to dab the brush against the container to convince them to move. Meanwhile, while you were distracted, more spiderlings were launching themselves skyward. More than a few escaped. More than a few, I’m sure, snugged themselves down in our clothing. It’s all good.

(Oops, just found one in my shirt sleeve. Now my office has some new residents.)

The end result is that we now have a known number of spiders in known volumes of space. We’ll track survival every few days to see how they fare. Once they get larger, we’ll spread them out a little more, but currently we find that the adults coexist nicely with two in a 5.7L container, so we’re hoping that the babies won’t fight and cannibalize each other at a somewhat higher density.

(Just found another baby under my shirt collar.)

Oh, no. My daughter and granddaughter are coming to visit for a week on Friday, and my wife has decided we have to make a more baby-friendly home. Which means…THE SPIDERS MUST GO. I tell her that the spiders were here first, so maybe it’s the baby who should make accommodations. That didn’t work. The baby will need to learn to love spiders eventually, so why not start early? No go. Maybe the baby would like to learn spider-catching technique, so you’re depriving her of a learning opportunity. Nope. So Mary’s been out in the sun room, destroying a happy, loving community by scooping up spiders and their many egg sacs, and has brought them to me. At least I’ve got a nice home for them in the lab.

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Neglected spaces are neat. The hotel I’m at is not neglected, so it’s kind of barren of spiders…except that there’s one unused space deep in the bowels of the building, which used to be a sports bar, and there’s a back side of that that has been totally ignored for at least a year, and the cobwebs are dense and beautiful, so I got to spend a little time poking around with my arthropod friends, rather than sitting awkwardly in a corner nursing a drink and wallowing in self-loathing as I usually do at social events. See, there’s hope for us nerds someday!

I usually skip this event at Skepticon, the Skeptiprom. I’m kind of a wallflower, and I don’t dance, but this year, I have a reason to go.

It was a good day. I did my usual spiderwalk, and found that the outside of the federal building (yes, I got stopped by the police again) was populated with these furrowed orb weavers everywhere. I caught a few, they were impressive.

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