Most of my cultures usually have uninvited creatures living in them. Spiders are common and usually do not cause problems. They may even help keep the culture more vigorous by eating the weak individuals. Sometimes the green peach aphid appears on coleus but usually I can find aphid parasites to release into the culture. Fungus gnats are very common but have never caused a problem.
Ants love to invade a mealybug culture if they can find a way into a cage and they usually do.
I have been very pleased using a pesticide called hydramethylnon for ant control. The best formulation for me has been Combat Ant Killing Granules. It is slow to solve ant invasions but will provide a very long period of control. Parasite vigor can decline in artificial conditions used to raise parasites. Eventually an artificial environment will select for those best suited for such an environment.