If you had scrolled down the google image search further you would have found a number of mycelial growths that look exactly like webs in your enclosure. see Mushroom EcologyIf these aren't what you are referring to then please provide me with a pic of what you mean.
Spider mites require live plant materials on which to feed and if not provided will either starve or leave. Dying leaves that are not attached to the plant are a poor source of food for spider mites.. They are extremely unlikely to be in the springtail cultures... Inside humid enclosures of any kind, you can see mycelia growths that readily imitate webs as there isn't the same kinds of pressures on them to develop into thicker structures.
Detrivore mites are extremely common and typically are introduced with substrates or plant that have not been adequately cleaned. It doesn't tale a lot of soil or substrate to add them to something. In a planted enclosure they are inevitable.