I walked into the kitchen the other day and there was a giant wolf spider right in the middle of the floor. My first thought was, who got loose, because I live on the third floor, far from the ground, and I have six wolf spiders right now. The one in the kitchen was a male – I could see the swollen palps. I had two males in the spider lab, but this one was way bigger than both of them. I caught the spider and went to investigate my collection. The two males were accounted for. One enclosure, labeled “immature wolf – Jacksonville, NC”, had the lid slightly ajar to regulate the humidity. This HAD to be the one., and it was. The enclosure was empty, but I did find an exuvium, or molt, and realized what happened. Just a day prior, the spider that lived in that enclosure was not big enough to reach over the edge to get out. That’s why I thought it was okay to leave the lid cracked. After it molted, its legs were MUCH longer and it easily crawled out to explore the great unknown. From the spider lab, the kitchen is a bit far, so he was definitely cruisin’! I’m glad I found him before the cat did!
Rearing spiders offers many surprises. I know, for many people, the sudden appearance of a spider is the very thing that freaks them out, but I see it all as Spider Magic; now you see it, now you don’t, or, you didn’t see it, now you do! They molt, mate, lay eggs, and build webs all right under our noses, but we rarely catch these life events. Alakazam! These things seem to happen out of nowhere. You just gotta be in the right place at the right time. Even though I observe spiders quite often, I have rarely seen spiders in the middle of molting. And I’ve probably seen spiders in the act of making egg sacs twice, ever.
The behind the scenes of how a spider grows and develops is really interesting and especially fascinating when you actually see it right before your very eyes! Let’s start with the magically appearing egg sac. I have two brown widows (Latrodectus geometricus) that I caught in North Carolina this past fall. These spiders are insanely prolific and can produce multiple egg sacs from one mating. Since November, I’ve removed nine…whoop, make that TEN as of today, total egg sacs from their enclosures. You’d think with that much activity I would have caught a glimpse of one of them in the middle of something. Nope! It’s all ABRACADABRA!
An egg sac can contain many, sometimes thousands, of individual eggs and the sacs can be bigger than the spider! Sacs may look like teardrop-shaped paper bags or cottony, bluish spheres. Sometimes, they look like silken vases, or flat papery discs. Some spider moms protect their sacs, some don’t, but they are committed to the process of creating their sacs with special silks and special care. For a little more info on egg sacs, visit my story “The Egg Sac Gallery”.
In the case of wolf spiders, the spider makes a mat of silk, lays the eggs on the mat, covers the eggs with silk and then wraps it all up into a little satchel which is then toted around attached to mom’s spinnerets. I was finally able to see some spider magic in the making when I noticed one of my female wolf spiders rocking back and forth in the same spot…constructing an egg sac! I checked in every ten minutes or so with camera ready! Sometimes, she would just be sitting next to the silk mat, sometimes feeling around the yellow mass which were the eggs.
Seeing no change after a few hours, I went to bed and woke up the next morning expecting to see it finished. Instead, I found that she had abandoned the sac for reasons unknown, It looked exactly as she left it. I would’ve loved to see the part when she rolled all the eggs into a silk ball and the moment she attached the sac to her spinnerets and took her first awkward, steps. At least I got to see some of it. On a happier note, I have two other female wolf spiders, different species, that both surprised me with fully finished egg sacs! PRESTO! And the magic continues!
Another magical spider life event is molting, All spiders molt or shed their exoskeleton as they grow. They go through instars, kind of like the stages of insects that undergo incomplete metamorphosis. Spiders can have approximately five to nine molting events (Foelix, 2011). After the final molt, the spider is fully grown and will eventually die of old age. How many times a spider molts depends on the type and sex of the spider. Male spiders have fewer molts than females. Tarantulas will molt even after they are mature providing an unlimited supply of cool exuviae (the scientific term for the old exoskeletons) to show people at presentations.
Molting is a very vulnerable time for spiders and they always seem to know when nobody’s lookin’. It can take hours to complete for larger spiders. During this time, the spider is utterly helpless and an easy target for predators or even opportunistic scavengers because they can’t defend themselves. If there is an issue, say not enough humidity, and the new exoskeleton hardens before they have pulled out of the old one, the spider can end up deformed and possibly die. I’ve found many spiderlings from different families dead in mid molt from invisible complications. Not only do spiders molt their entire exoskeleton, they also molt the lining of their stomachs and esophagus. That’s amazing!
I have never seen a tarantula molting outside of YouTube where one can find many videos of this phenomenon. Finally, this past year, Chandra, my chaco golden knee tarantula, was caught in the act! She was an adult when I got her. I have no idea how old she is. She molts approximately once a year. It was early evening and I just happened to glance over at the enclosure and there she was upside down laying on her back! The upside down thing is crazy if you’re not expecting it. Non-tarantula spiders will dangle off of a dragline thread to molt. Tarantulas don’t produce that type of silk and would probably be too heavy anyway. This way has worked for them for millions of years, as cumbersome as it seems! Here is a video of an orb weaver molting using the dangle method.
Seeing one of my own tarantulas molting was way cooler than watching someone else’s tarantula molting. I got my camera ready and nestled down to watch. It was a very slooooow process. Molting begins with the carapace popping open at the distal seam, kind of like a lid. The abdomen comes free and then the appendages are pulled out with a very subtle pulsing action that you can only see in a sped up video. It doesn’t look fun for the spider, at all. My excitement soon turned to anxiety. It looked like she was having trouble! Her legs on one side were out way more than the other and she was right up against the side of the enclosure. I was tempted to intervene and move Chandra, just scootch her over a tad, but I knew I shouldn’t touch her. I referenced Arachnoboards and googled “tarantula having trouble molting” at least three times to make sure. Everything I found confirmed NOT TO TOUCH her. Two hours later, she managed to free herself and all was well, but it wasn’t as fun as I thought it would be. Here is a time lapse video that took about forty-five minutes to film. It was so stressful! I would’ve rather had the ‘PRESTO CHANGO – NOW THERE ARE TWO!” experience instead of the slow details!
Spiders can make lost limbs reappear after a molt as long as it’s not their last molt. I found an immature orb weaver one summer that was missing its first two pairs of legs. It was the most awkward lookin’ thing! It didn’t even move like a spider. This little guy (or gal) might have just barely escaped a predator…or maybe it was the result of a bad molt? In addition to making lost limbs reappear, they can also make them disappear using a trick called autotomy. It’s the same thing lizards do with their tails. Well, after some time in captivity, the four-legged orb weaver molted and SHAZAM – Four New Legs! I read about how this happens. The new legs were already developed and folded accordion-style inside the old leg stumps. When the old exoskeleton is shed, the new legs can stretch out! They’re smaller than the other legs at first, but if they are young and there are more molts to come, the legs will eventually grow to match the original leg size. It boggles my brain that they can do that!
Spider magic can be fascinating to some, yet startling to others. The sudden appearance of a spider in the house has a backstory that’s more colorful than you realize. Arachnologists and dedicated enthusiasts have taken the time to reveal the secrets behind the spider’s “sorcery”. During this writing one of the brown widow egg sacs erupted in many, many babies! VIOLA!! We have a cloud of brown widow spiderlings out of nowhere, BUT there were weeks of silent development happening out of sight. The spiderlings hatched days ago and all had their first molt while still inside the protective sac.
There is much you don’t see prior to showtime i.e., finding a giant wolf spider in the middle of the kitchen floor. These egg-legged magicians deserve applause! I think back on some of the magic that I loved when I was a kid; the tooth fairy, Santa, etc. I miss them. The magic was definitely exciting, but I was relieved to learn how it was done – how is Santa getting in here without a fireplace, or how does the fairy even know my tooth fell out? When a spider pops up out of the blue, think of it as being on the VIP guest list and enjoy the show!
Akamu Jude Ewunkem*, Agee Kyle and Rivera Kayse
Department of Biological Sciences, Winston Salem State University, Winston Salem, North Carolina,
USA; https://www.peertechzpublications.com/articles/GJZ-7-123.pdf.
Foelix, Rainer F. Spider Biology, third ed. New York, New York: Oxford University Press; 2011.
Shultz, Stanley A. and Shultz, Marguerite A. The Tarantula Keeper’s Guide. Hauppauge, NY: Barron’s Educational Series, Inc.; 1998.
SpiderMentor 
Great post, thank you! I love the drama of molting… when it works. I wish I knew the secret of appropriate humidity, it seems key. Too moist is bad, too dry is bad. I’ve had a few sad failures over the years, but as you say most often it is accomplished when I’m not looking.
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