A Neospintharus Tale

This is a story about luck, transformation, and opportunities (or the lack thereof) in the life of a peculiar spider, Neospintharus trigonum. These spiders are in the Theridiidae family AKA comb-footed spiders and/or cobweb spiders. I found one in my backyard (Pgh) in mid-May. I only spotted this speck of a spider because it was hanging between two planters, the very planters I was about to use. Its beige colored body, with its legs pulled in tightly, stood out against the dark table.

Typical resting posture of Neospintharus trigonum. It’s upside-down and facing to the left.

There is no common name for Neospintharus trigonum, so I nicknamed it Neo. Neo is small, no larger than four millimeters and isn’t your typical, everyday spider. It has a triangular-shaped abdomen and is really skinny if you’re looking straight down on it. There was no web, just a single strand of silk by which Neo hung upside down, body dangling in the breeze. To anyone (or anything) who wasn’t paying attention, Neo could have easily been passed off as a piece of tree debris caught in a remnant web.

Finding a triangular-shaped spider in the field guides was pretty easy. There aren’t many that sport that odd shaped body. In Richard Bradley’s Common Spiders of North America, there is a drawing of an adult female and an adult male Neospintharus trigonum, but the adult male has crazy projections sticking out of its head, like a unicorn, but with TWO horns! Maybe more like a rhino. Under the scope, I was able to tell from the swollen palps that Neo was male. Clearly, Neo didn’t have any crazy rhinoceros projections so I figured he was a sub adult male which meant he had one more, final molt to go before he’d get his horns. I could hardly wait to witness this odd transformation! While dipping into the the life history of Neo, I learned there are only three species of the Neospintharus genus found in the United States. Baboquivari is a western US species and furcatus is a southeastern species, so I’m fairly certain I had Neospintharus trigonum, native to our region!

In the meantime, while waiting for his final molt, Neo wasn’t exceptionally exciting to watch. Housed in a 5.5 oz Solo cup, he continued to hang upside down with his legs folded over his body from a single thread across the top. He didn’t make an additional web of any sort and he didn’t move around very much. I would put a few fruit flies in his enclosure a few times a week but never saw him eat. I learned that these kinds of spiders are often kleptoparasites which meant Neo’s style was more like sneaking into other spider’s webs and eating the pre-packaged food or any insect debitage the host spider ignored. Maybe that would explain his odd shape and lack of movement. This dude was all about the stealth!

Later that month, eighty miles north of Pittsburgh near an abandoned railroad bridge that crosses the Clarion River, I ran into another Neospintharus trigonum which happened to be dangling at eye level off of a shrub. What luck! At home, I was able to confirm that I had a lady Neo! I had to put her under the microscope to see the bottom of her abdomen to determine the sex. I could also see two small points on the tip of the abdomen, another diagnostic feature for this kind of spider. I called her “Femneo”.

As luck would have it (possibly not luck, but seasonal timing), that weekend, the male Neo molted and BOOM, all of the sudden, he had two horns on his head!

I had to ask, what is the function of this structural metamorphosis? It must have to do with mating since the horns appear only when the male is mature. Note that the females do not develop these projections. Down the rabbit hole I went and I came back out with some fascinating stuff! Apparently, there are glands in the adult male projections that come into direct contact with the females fangs during copulation. It is thought that the glands produce pheromones that pacify the female. Wow! Studying spiders is a never ending world of awe! It was time to play match maker!

I introduced Neo into Femneo’s enclosure, also a 5.5 oz Solo cup. As soon as Neo touched the silk, he immediately stopped clambering around and started to wave his long, front two legs. Femneo was only about a centimeter away and noticed him, too. She moved towards him and they both started the leg waving. The leg waving seemed more like a feel thing rather than a visual thing that the colorful, sight-advantaged jumping spiders do. There was more going on than my own sight-advantaged nature could perceive. In addition to whatever pheromone action that could’ve been happening, these kinds of spiders have stridulatory ridges on their carapace and abdomen that will make vibrations which can be important for courting.

Female Neospintharus trigonum on the left and the male on the right.

Millimeters apart, just when I thought they liked each other, Neo suddenly bailed and dropped (a very common spider getaway tactic). I thought maybe he was being overly cautious, but a few moments later, when Neo advanced, Femneo swung her abdomen forward and wheeled her back legs in an attempt to bind him! Neo dropped again and barely missed being a meal! I quickly removed him from Femneo’s quarters and decided I should make sure Femneo had a meal before I try this again. Here’s the actual footage from that encounter.

Remember how I mentioned that Neospintharus is usually a kleptoparasite? That means they need another spider as a host so they can steal their food. I also read that Neospintharus spiders will sometimes eat the host, a thing called araneophagy. This made me nervous because as stealthy as these spiders are, there is still a chance they could be discovered and eaten by the host spider and I didn’t want that to happen. There are a lot of common house spiders (Steatoda triangulosa) that share my home and I happened to know there was one in the kitchen behind the cat food tin. I captured the spider, which was a little bigger than Femneo, and let it drop into her Solo cup thinking it would: (a) settle in and make its own web from which Femneo would scavenge, (b) Femneo would eat the other spider, or (c) other spider eats Femneo – which wasn’t gonna happen under my watch!

The house spider landed close to Femneo and immediately froze. Had it sensed Femneo? Neither spider moved for nearly ten minutes. The house spider moved first. With every movement it made, Femneo would match the timing moving towards it and would stop when the house spider stopped. It was very much like how a cat stalks. Both spiders seemed to be aware of each other. Their movements were slow and purposeful which was different from the scrambling movements both exhibited when I first captured them. To my surprise, without an established web of its own, the house spider attempted to wrap Femneo when she got too close. Femneo dropped and made a hasty retreat but the house spider followed! I quickly interrupted and removed the house spider. WHEW! THAT was a fail.

I later added a few of the many spiderlings I’ve been rearing. They were no match for Femneo. When they got close to her, she’d tap around with her front legs like antennae. When one of the spiders was within leg reach, Femneo would quickly swing her body forward and, with her back legs winding, she’d wrap the smaller spider. I also offered Femneo (and Neo) less dangerous fruit flies, but neither accepted them. Neo wouldn’t eat at all but Femneo quickly dined on other smaller spiders. I didn’t want to put Neo in with another spider as it would be a potential predator. There was a chance, as an adult male with the primary mission to mate, he wasn’t even hungry.

Neospintharus trigonum female wrapping up spider prey!

Now that Femneo was satiated, I reintroduced Neo into her enclosure three more times after the initial fail. Each time, they would avoid one another. I spent a lot of time observing them: during coffee in the morning, on a lazy Sunday afternoon, at night while listening to audiobooks, at dinner time waiting for the fries to bake. I began to wonder maybe Femneo wasn’t mature? Maybe she wasn’t even Neospintharus trigonum?! I went back and confirmed, she was the right lady. They just didn’t hit it off. I wondered if they recognized each other each time. They didn’t explore with their front legs as much as they did during their first encounter. I wish I had another Neo male to introduce to see what would happen. Was she being selective? Maybe his rhino horns weren’t right.

On June 18th, my luck (and Neo’s luck) ran out. I found him dead at the bottom of his enclosure. It could’ve been old age. Males spiders have a shorter life span than the females. What a huge bummer! I was looking forward to seeing the whole life cycle! I’ve read about it, but witnessing their behavior would be way more exciting. If they had mated, Femneo would’ve went on to make an egg sac. Not just any ol’ egg sac, but a tiny woven vase (you have to pronounce it /va:z/ to give it the right effect). She may have made two. And then there would’ve been Kidneos.

Female Neospintharus trigonum with her egg sac. Photo by Kim Fleming. Used with permission.

I released Femneo to the backyard onto the dead branch of a giant spruce at eye level so I could get one last picture of her. Within minutes, she was far up over my head climbing quickly along the twigs. She floated down on some silk and then, as if out of nowhere, she detoured along another invisible thread. Up and up she went, like an acrobat, until I could barely see her anymore. I learned that even though these spiders were very small, they used a lot of space! “Needs larger containers” will be in my Neospintharus-keeping notes for (hopefully) next time.

Femneo released! She was about three feet above my head. She’s on the tip of one of the smallest twigs to give you an idea of her size.

I thanked Femneo her for her time in captivity allowing me to get to know her. I’m sure she’s going to find a nice spider host, possibly one of the Orchard spiders I’ve seen among the branches of that same tree. Maybe she’ll find another male. Maybe we’ll cross paths again. The key is to always be looking! This summer, when you see an orb web (the classic wheel and spokes web) check the fringes of the web for a small speck that looks like a piece of tree debris and if you’re lucky, you may find your own peculiar Neospintharus trigonum!

Sources: Agnarsson, I. (2004). Morphological phylogeny of cobweb spiders and their relatives (Araneae, Araneoidea, Theridiidae). Zoological Journal of the Linnean Society 141(4): 447-626.

Agnarsson, Jonathan A. Coddington and Barbara Knoflach, (2007). Morphology and evolution of cobweb spider male genitalia (Araneae, Theridiidae). The Journal of Arachnology 35:334–395.

Bradley, Richard. Common Spiders of North America. Berkeley, CA: University of California Press; 2013.

Exline, H. & H. W. Levi, (1962). American spiders of the genus Argyrodes (Araneae, Theridiidae). Bulletin Museum of Comparative Zoology Harvard 127: 75-204.

Ubick, D., Paquin, P., Cushing, P.E. and Roth, V. (eds). 2017. Spiders of North America: an identification manual, 2nd Edition. American Arachnological Society, Keene, New Hampshire, USA.

Clypeal gland. (2020, May 8). Wikipedia, the free encyclopedia . Page consulted on 12:15, May 8, 2020 from http://fr.wikipedia.org/w/index.php?title=Glande_clyp%C3%A9ale&oldid=170598211 .

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