The culprit of the yellowing of the tips of spider plants is the phytotoxin. This is a natural plant toxin that acts as a defense against insects and other plants. The toxin is secreted by the petals in the case of some other plants. It is present in small amounts in most cases, but if it is over-produced, the toxic effect is spread throughout the plant. The effect usually manifests itself after two to three weeks, but can occur before then. You can either apply enough to kill the insects or grind up your spider plant and use that powder on top of your soil. In either case, don’t worry about accidentally applying pesticides too, as these could cause damage to your homeplants.