I have a new succulent that I'm taking care of, but over the past couple of weeks it has been picking up some fluff that looks a bit like mould but that I believe is cobwebs of tiny spiders. I've read about spider mites, and so I'm wondering:
Yes, it looks like botrytis...a gray mold. You should take the plant out, wash off soil and mold. Throw away all soil, gravel, rocks and bleach the glass bowl. Get soil for succulents and replant. I don't think your plant looks like it will make it. Succulents in a non-draining medium can only be watered a tiny bit and only when the soil is completely dry. Don't spray water for humidity either. You might want to try spraying your plant with NEEM. It acts as a fungicide and also coats the plant's leaves to prevent too much transpiration and thus reducing stress. Use soil or infuse your new soil with michorrhyzae, bacteria. Water with a little fish emulsion. Otherwise don't fertilize with anything else. Fish emulsion is 5-1-1 which adds a little of the nutrients the plant needs but fish emulsion seems to give plants more...strength. Science hasn't figured out why, that I've heard about, but worth a try and can't hurt. Once the plant is healthy and doing well you can think about a proper fertilizing program. It should be extended release and VERY light. That plant has no where to grow, anyway. Consider it a 'long term perishable' unless you use another pot. If you do, choose a short, squat, clay pot with companions that are also shallow-rooted, cactus-type plants. During the summer, placing your indoor plants on a protected porch that gets a lot of light, little wind, no rain, little access by critters helps them rejuvenate and therefore last longer and look better. Indoor plants are considered long-term perishables but this summer vacation helps them last almost indefinitely. Keep an eye out for insect infestations (get a 10X magnifying loop) and check the undersides of the leaves, carefully. For plants that have draining pots, give them a good shower in your shower, let dry and put them back out. Allow soil to dry out before watering. Some plants need some moisture at all times others do not. Get to know your plants, well. Also, re-pot your plants with new soil once a year, don't put rocks in the bottom supposedly to improve drainage...this does the exact opposite by causing a 'perched water table'...and never put a small plant in a large pot. Upgrade your pot by making sure it is only a little, a few inches bigger than the old pot. Good luck...
Does this plant have roots? (Can you pick it up without digging?) You may have an air plant on your hands. In the future don't let it rest on water - they will rot when in direct contact with water over long periods of time. It will absorb humidity from the air, but you should soak it every now and then when it looks dry.
I can't identify which plant that is, but it looks like some kind of succulent, do you have a botanical name for it? The white stuff you're describing as webbing looks more like fungal growth in this photograph - if the plant is a succulent, they do not like damp conditions, so I'd expect to see it going mouldy, so to speak...
