Why does Santa come down the chimney?

To look for spiders, of course. Mary and I were getting into the spirit of the season and were surveying the area for spiders this morning. We were heartened by the fact that she discovered a salticid in our house — I’d given up on looking, assuming that no self-respecting spider would be out and about in late December in Minnesota, but there it was. So we donned our headgear and started scrutinizing window frames and dusty corners, and we also trooped over to the science building on campus and checked out the hallways and the basement.

Mary caught me in dynamic action pose, staring at cobwebs.

Unfortunately, the spider population was sparse or in deep hiding. We found another salticid in my office, and the husks of a few dead pholcids (lots of pholcids thriving in our basement, though), but no Theridiidae. There were also a few abandoned funnel webs outside. One problem is that the university custodial staff do a really thorough job of demolishing cobwebs and making an inhospitable environment for spiders…and I don’t think there are very many insects to eat there, except maybe in relatively unreachable places, like crawlspaces.

It’s also cold outside. I’ll be interested to see how the population changes in the Spring.

Calf Bug-ropin’ with Cowboy Vera, Spider-style

I was bragging about Vera’s great skill in capturing multiple prey in minutes, so I thought I’d show you. Basically, whenever I put live flies in the spider’s vial (I feed her 3 times a week), she is off like a shot, immediately charging in to snare them.

She reminds me a lot of my cat that way.

It was tricky keeping her in frame and in focus, but I think you’ll get an idea of how spiders use their webbing to immobilize prey.

Also, I’m going to start doing everything “spider-style”.

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Baby spider

Quick update: here’s a shiny new Parasteatoda postembryo. Nothing exciting happens in this video — it’s nothing but 3 minutes staring into the eyes of a baby spider. It twitches a bit. It waves a leg around, floppily. But so much is happening in its nervous system!

This is one member of the new clutch of Gwyneth’s grandchildren. I’ll be sorting them out this weekend and putting them in individual vials, and maybe by early March they’ll be making Gwyneth’s great-grandchildren.

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Spider Report: Vera, rodeo star

I just got back from tending my herd, who are all doing well. I’m anxious to get more egg cases, though, so I’ve been feeding them more and frequently — I gave each vial of spiders a half dozen flies today. I noticed some behavioral differences. The young adults each quickly moved on a fly, immobilized it, and settled down to biting and eating. Vera, currently the most senior spider in the colony, had a different strategy: she would scurry over to a fly, quickly wrap it up, and then move on to another. She had 5 flies immobilized and writhing in lightly webbed cocoons in about 30 seconds. It reminded me of calf-roping at the rodeo. I was impressed. Then she rubbed her forelegs together and cackled something vulgar in spider language* before moving back to her first captive and turning its guts into soup.

The embryos in the one egg sac I have are coming along nicely, showing nicely differentiated legs. I’m avoiding manipulating them much, since I’m more concerned about getting a strong, healthy third generation going, but they look to be about stage 13-14 by the standard staging series, which means I’ll probably have post-embryonic spiderlings by this weekend, and am going to have to spend a bit of time sorting them out into separate vials. This cohort of spiders are all inbred grandchildren of Gwyneth. I’m sad to say that Vera has not managed to produce any viable offspring for the colony — I did hear her sneeringly announce that she was not a breeder, and in particular wasn’t going to breed to produce servile offspring for an inferior species.

I’ll put the diagram of the developmental stages below the fold, so arachnophobes may not want to go any further, even though these are cute li’l babies in the image.

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Spiders in Space

Oh, the nerdity of it all. I just read about a discussion of how spider-aliens would survive in space. This is my kind of thought-experiment!

In my stellar empire, the sapient life of the home world are arachnids. Due to an oxygen-heavy world with certain evolutionary characteristics, spider-like beings developed intelligence and formed society, leading them (eventually) to start looking toward the stars. This led to the development of space suits for the pioneering arachnid astronauts.

What would these look like? How would space suits be differently designed to support arachnids?

Let us posit that the arachnids are roughly 4 feet from “spinneret” to fangs. Their legs are large enough to support them (I don’t know what that is). They’re light compared to us (maybe 25 pounds at the heaviest – bear with me on the whole square cube law deal). They have roughly equivalent technology levels to ourselves at the time of our first missions into the stars.

Just by coincidence, I’ve been reading up on spider physiology recently, so this piqued my interest. Most of the answers in that thread are pretty good.

I’d first have to state a caveat: multi-legged alien beings evolving on a distant planet will not be spiders. It’s unfair to compare limitations and abilities that they have to those of terrestrial spiders — they aren’t related! Just blowing up an Earth spider to 1.2 meters long is not a valid comparison. But OK, let’s play a game and imagine an alien “spider” that evolved from an ancestor living in a similar niche to that of our spiders. Traits that are probably relevant are:

  • Obligate carnivory. It’s a predator with a need for live food. Unless there’s a way to store frozen bug juice shakes that this species will willingly eat, this sounds like a big problem — space-faring “spiders” are going to have to bring along along bug ranches to maintain livestock. And food for said livestock. Forget the spacesuits, there are going to be some demanding requirements for life support on space ships.
  • External digestion. Why, you might ask, would they need live food? Spiders inject enzymes into their prey which break down the guts of the animal into a liquid soup that they can slurp up. The food is both the container and the meal. “Spider” Tang is going to be a tough recipe.
  • Ambush predator. This has pluses and minuses: most spiders have notably lower metabolic rates than other poikilotherms, about 70% of what is expected in animals of equivalent size. So, lower oxygen consumption — that’s great for spacecraft/spacesuit design. On the other hand, they can have extreme surges in activity, for instance, when prey is captured. Oxygen consumption is going to be somewhat unpredictable.
  • Pulmonary system. The linked discussion mentions how spiders often have a dual respiration: they have two or four book lungs in the ventral abdomen, but also many of them have a trachaeal system, an array of small tubes that penetrate the cuticle and permit atmospheric gases to flow in to the tissues. This one might not be a problem, though: trachaeal systems are less and less effective the larger the animal, and they rely more on discrete respiratory organs, like lungs, as they grow to a larger size. At 1.2 meters long, these alien “spiders” are almost certainly going to have “lungs” and “nostrils” — it’s just that if they’re like our spiders, they won’t be on the face, but low on the abdomen.
  • Respiratory pigments. This is where it becomes obvious that you can’t simply extrapolate from Earth spiders to space “spiders”. Our spiders use hemocyanin to carry oxygen, which has a significantly lower O2 carrying capacity than our hemoglobin. You’d think along the way to evolving larger size and metabolically demanding intelligence they’d have to be using a more efficient respiratory pigment…although blue-green blood is kind of cool.
  • Sensory apparatus. Look closely at a spider sometime: they are covered with hairs. These aren’t dead insulators like our hairs, either, but are all invested with nerves for mechanical and chemical sensory functions. Putting them in a suit that limits them to only visual input is going to be like dumping them into a sensory deprivation tank.
  • Motility. There is a suggestion that they could use “an enclosed pod that the spider can sit inside with legs folded and have mechanical arms/legs that support the pod and allow it to walk around.” Maybe. But that throws away many of the virtues of a space-walking “spider”. They are incredibly agile, are accustomed to maneuvering in 3 dimensions, and are beautifully adept at manipulating objects in their environment. Watch one wrap a prey item in a web — they are weaving with all 8 legs simultaneously, flipping it around and dancing about delicately. It would be a shame to limit that by stuffing the “spider” astronaut in a barrel and making it manipulate its environment with a few waldos.

It’s a fun exercise, but if we ever find such a creature I suspect it will have less similarity to our spiders than we humans do to an acorn worm, so much of the speculation is moot.

Real spiders are more interesting. As I said, I’ve been reading up on spider physiology, so here’s a diagram of the main elements of the spider circulatory system (“h” marks the heart, on the dorsal side of the abdomen.)

That’s the cartoon version — here’s a resin cast of the full circulatory network of the opisthosoma of Cupiennius. It blows me away that they were able to do this — Cupiennius is fairly large as spiders go, but still pretty tiny.

Even more impressively, people have measured the blood pressure in the spider circulatory system — no, not with an itty-bitty sphygmomanometer. I suspect they used optical methods to visualize pressure changes, but that’s a paper I haven’t tracked down yet.

Systole and diastole are still valid concepts in a spider. In case you were interested, their hearts beat at a rate of 9 to 125 beats per minute. That’s quite a range, but as I mentioned above, one of the challenges is a highly variable metabolic rate.

Ultimately, though, if you’re going to design an SF “spider”-like alien, you shouldn’t be constrained by the form and physiology of terrestrial spiders. A homeothermic creature with an endoskeleton, but with a bunch of limbs and eyes and a sclerotized cuticle, and maybe some funky spiky complex mouthparts, is going to look enough like a spider to Zapp Brannigan that that’s what he’s going to call it anyway.

Schmitz A (2016) Respiration in spiders (Araneae). Journal of Comparative Physiology B 186(4):403–415.

Wirkner CS, Huckstorf K (2013) The Circulatory System of Spiders. In: Nentwig W. (eds) Spider Ecophysiology. Springer, Berlin, Heidelberg.

Santa, all I want for Christmas are spider eggs

When I got home from my week in Denver last night, the very first thing I did was rush off to the lab to check on the spiders. They were fine! Completely unperturbed by a week of neglect! They even produced egg cases for me! Well, one healthy egg case. Vera continues her habit of dumping dessicated dead eggs in ill-formed egg cases, which you may recall was something Gwyneth did before she died, too.

Oh, yeah, then we checked on the cat. She was fine, too.

Spider update

All I want for Christmas is another egg sac, and they aren’t obliging.

  • Vera ate another husband. Again. She’s the voracious jaws of death, and all I can hope for is that the poor doomed fellow inseminated her before getting sucked dry. Vera is hugely bloated right now, having consumed a large male and a smorgasbord of flies.
  • The other pairs of spiders are much more placid and are coexisting well, but no eggs yet. I did notice that one of them had molted, so maybe they’re too young? Have I set up a Blue Lagoon scenario here?

  • All of the spiders (except those sacrificed to the bloodthirsty Vera) are looking healthy and active, and are quite swift in demolishing flies presented to them.

So I’m just waiting. Waiting waiting waiting. Don’t they realize I’ve got plans for their progeny?

Now thinking about starting up a dairy spider farm on the prairies of Minnesota

There are these weird salticid spiders that have evolved a radically different morphology — they live in ant nests, and physically mimic the ants. Look at this ant-spider. Isn’t this amazing enough?

That’s a spider? Yeah, count the legs. It’s trying so hard to fit in with tunnel-dwelling insects with three body segments, you just have to applaud the effort.

What’s more, they’ve acquired another evolutionary novelty: they secrete ‘milk’ to feed their young, and have extended parental care. The necessity of milk production was tested with the cruel experiment of painting over the epigastric furrow (the site of secretion) with White-Out, and what happened? All the spiderlings starved to death. The utter bastards. There are things you can get away with when working with invertebrates that you couldn’t do with cute fuzzies with bones. Try doing that experiment with bunnies, just be prepared for torches and pitchforks.

There’s another revelation in this figure caption.

Spider milk and its secretion site in Toxeus magnus.

(A) Ventral view of mother. (B) Milk droplets secreted after slight finger pressure on abdomen.

Did you get that? They are milking spiders. I come from a long line of Norwegian dairy farmers in Minnesota, so you can guess where my mind went from here. Can I get state and federal subsidies for my spider farm? I’ll have to look into it.

The study is primarily about the life history of this spider species, with some experimental manipulation, and it does a thorough job of that.

T. magnus offspring body length growth and food resources during development.
(A) Egg hatching. (B) Absolute milk dependence: Spiderlings do not leave the nest, and the mother releases milk droplets to the nest internal surface. (C) Spiderlings forage during the day and suck milk at night. (D) Subadults nutritionally independent but still return to nest. (E) Spiderlings reach sexual maturity, but some stay with the mother. *The mother. N = 207 offspring, Nnest = 19 surveyed nests, error bars (SEM).

It’s missing one thing, though: any analysis of the chemical make-up of spider milk. I’m going to take a wild guess that unlike mammal milk, which is rich in fats and carbohydrates, spider milk is going to be more like a protein shake — that it’s going to be in many ways similar in composition to the dissolved bug guts that spider adults live on, to simplify the transition from an independent hunting spiderling to a spiderling with an obligate dependency on parental care. Which means a) humans can probably synthesize it by homogenizing masses of fruit flies in a blender with some digestive enzymes, and filtering out the chitin, and b) there’s not going to be much of a human market for it. Alternatively, they suggest that spider milk may have evolved from the breakdown of trophic eggs — that is, eggs produced that do not develop, but provide a food source for other members of the brood. In that case, it may be a soup of phospholipoglycoproteins, similar to the vitellogenins of other arthropods, and its closest vertebrate analog would be egg yolks.

Inquiring minds want to know. They’re going to have to milk a lot of spiders to get enough to analyze, though!

Chen Z, Corlett RT, et al. (2018) Prolonged milk provisioning in a jumping spider. Science 362(6418):1052-1055. DOI: 10.1126/science.aat3692

P.S. There is a Minnesota milk song. They might have to change some of the hand gestures.

Spiders will just break your heart

Last Wednesday, I was so optimistic. I’d paired up Vera with a first-generation son of Gwyneth (GI-♂), they’d gone at it hot and heavy, and had produced an egg sac — an egg sac with a peculiarity I’ll get to in a moment. My plan was to go in today and open up the sac and see what embryos I’d find.

The peculiarity was that although I’d classified all my spiders as Parasteatoda tepidariorum, there was still a little uncertainty. The patterns of pigment on their cuticles were a bit ambiguous. Here’s part of the description of P. tepidariorum from Common Spiders of North America.

This is a medium-sized to large cobweb weaver. The abdomen appears teardrop shaped as the spider hangs updide down in its web, spinnerets uppermost. The cephalothorax is tan or brown. The abdomen color is extremely variable, usually shades of light brown with a mottled tan or brown. Some individuals are nearly black, others unmarked and pale. The legs are darker at the joints.
…
The egg cases of this spider are tan and tardrop-shaped, point uppermost.

This describes my spiders perfectly, given that there is variability in the patterning of the abdomen. They look different, which had me worried that I may have gathered a couple of different species, but then the description of the egg case settled it for me: Gwyneth had produced lovely tan, teardrop-shaped egg cases. Case closed, right? Gwyneth and her progeny were P. tepidariorum.

Then Vera produced an egg sac. Vera herself also fits that description of P. tepidariorum to a T.

But the egg sac she produced was a cottony, pure white ball. What? I flipped through my books looking for some indication of what this might mean, and found a description of Steatoda triangulosa, which is also common in this part of the country.

This is a medium-sized cobweb weaver. The cephalothorax is reddish brown. The legs are light brown with dark brown bands. The apdomen is light brown with two rows of angular spots or bands of dark reddish brown separated by white areas with a mottled appearance. In some individuals this pattern looks checkered.
…
The egg case is a fluffy white sphere.

Uh-oh. Are Vera and Gwyneth from two different genera? There’s nothing in Vera’s abdominal pattern that fits S. triangulosa, but maybe that’s highly variable in this species, too, and the egg case definitely fits this description. But she’d bred with P. tepidariorum! Were the new eggs hybrids? Was I just a terrible ignorant klutz playing the taxonomy game poorly? I went into the lab to take a few steps towards finding out.

And…disappointment. The “fluffy white sphere” was gone — it had been torn apart. The eggs within were dried up lumps. Uncertainty reigns.

I put the two lousy parents into a petri dish and made a video. You look and tell me: Parasteatoda tepidariorum or Steatoda triangulosa? Looking at just the adult morphology, I’m saying P. tepidariorum, but what do I know. Video below the fold, with an agitated pair of spiders scurrying about.

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Happy Spider Report: Vera was preggers!

It’s all good news. All the spiders are thriving right now, chowing down on flies. Vera produced a very pretty egg sac — I’m thinking the 14/10 light/dark cycle may have something to do with it — and has shrunk to about half her previous size. I’m planning to open up the sac on Sunday as part of my devotional, just to check on the health of her embryos. Although I’m low on adults, the next generation is coming along, and with any luck I’ll have a swarm of spiderlings this time next week.