Jeff watched herself change into the same form as the woman in the picture displayed. She finally stopped her vertical growth when she now was only a foot or so lower than the ceiling. By now, her ass had become truely massive, pushing out to nearly 10 feet behind her and was turning into a solid mass.
Her feet pointed downwards and then curled even further backwards at her ankles, while they turned pitch black. Her toes merged forming a single point. Once that hallened, her legs folded back at her knees and curled even further, until Jeff was now kneeling with her "feet" pointing upwards a bit. Her former ass was now so large that it made it so that her calves were not actually touching the ground though, and now matched her legs in color. 8 new protrusions formed along her "ass's" sides, extending outwards into long but thin cones. Then bending near the half way mark downward, forming her knew knees.
Carefully, Jeff tried her best to stand up on her 8 new legs, and found that even with her size, she felt much lighter than what she expected, so it wasn't too difficult to stand up. She also found that walking on her 8 legs was almost instinctual to her, and could even do more complex maneuvers like jumping side to side with ease.
All while this was going on, Jeff didn't notice that she now had become the proud owner of a nice pair of H-cups too. However maybe it was the fact that she wasn't human, but to her, they didn't feel heavy at all, and actually felt significantly lighter than what she had started with before she started becoming an arachne.
With one of her now delicate hands, she gently cupped one of them, and felt her hand sink in a bit before it started to lift up her boob. She could feel that there was a bit of breast milk in them too. Playing with her boob like this actually felt really good, and she could, no, would definitely explore all of that later, once the kids were out of the house of course.
The last things to finish off the transformation were the addition of her extra eyes, and her hair becoming almost a light, ash grey. The moment she finalized her transformation, the entire house around her started to change too. Everything opened up dramatically, and all of the doors became extra wide or double doors for her to fit through more easily.
Many new memories flooded her head as well. And while they didn't overwrite her old ones, they felt more like her real memories than her actual real ones. She vividly remembers having married Mike, how they dated for a long time prior to that, and how much she loved him for being one of the few people who were not terrified when seeing her. She remembered growing up pretty secluded to avoid causing mass panic at schools. And managed to teach herself well enough to graduate from highschool. She didn't mind it so much though. It had led her to meeting the man who now was her husband.
Even his kids were not too scared of her, although they were a bit at first, especially the youngest one. But now even she had come around and was no longer scared of her, as long as she didn't just appear near her, or was cast in poor lighting. Your stepson though... there was still some work left to be done with him, although that issue was a different matter than you being an arachne. No, it would seem that neither could he stand to be near you for too long or go without eventually staring at you. "Like father like son I suppose. Although only one of those two groups would have the pleasure of fucking me" Jeff thought with a mildly perverted grin on her face as she was remembering how nice it felt to fuck Mike, while she absentmindedly slid a hand down to her pussy, which was still nestled between her 2 former legs.
Jeff remembered that she had been somewhat extra horny these last few weeks, and it was beginning to come out in her day to day life. One of the unintended side effects of her secluded lifestyle was that she had gotten very accustomed to just masturbating and indulging in self pleasure the moment she became horny. Her body had slowly gotten use to several masturbation sessions a day, sometimes even slightly playing with herself to just keep a horny buzz going for hours at a time. Her sense of shame and embarrassment had been tossed out the window a long tine ago too.
However, now she no longer was alone. And was slowly working towards ridding herself of her bad habits. Especially her absentminded masturbation. However that had hit her sex drive hard. Now that it no longer was being immediately handled, her arousal slowly would build and build over time until she became so horny that having sex asap was all she more or less cared about, outside of all of the important topics, like her family's wellbeing and such.
Mike had made it his personal responsibility to attend to her needs at least once every day or two, but that was more like a patch job, than a solution. If this was the old her, she may have given in and fucked her stepson, but she was not about to ruin the happiest time of her entire life just to get herself off for a while. "Sorry boy, Mama's sexy body, boobs and all, belong only to her wonderfuk husband Mike and Mike alone" Jeff apologized in her head.