With spider mite numbers able to grow so explosively, you'll definitely want to know whether your IPM strategy is having an effect. Simply take a magnifying glass to quickly see how Spical is doing.
Spider mites often develop in hot spots, so you should release extra predatory mites in these places. This is also where you'll be able to see whether your strategy is effective. If it is, the affected areas won't grow in size. You'll still be able to see webs, but the spots won't become larger. The downside is that the damaged spots won't simply disappear. While this isn't such a problem for vegetable crops, it can lead to a loss of sales value for ornamental crops. However, if the crop continues to grow well after the infestation, the plants will, at some point, shed the damaged leaves.
Grab your magnifying glass
You'll need a magnifying glass to inspect your crop closely, as this is how you can identify both spider and predatory mites. They're usually on the underside of the leaf.
The mites are easy to distinguish from each other: spider mites are green or red in color, and the adults have two spots on their backs. They also move quite slowly. The predatory mites, on the other hand, move very fast. They're also translucent, a little white or sometimes brownish, and their body is pear-shaped. So if many more predatory mites than spider mites appear under your magnifying glass, you can be sure everything will be alright.
It's good to check whether you can find traces of eggs. Spider mites' eggs are completely round and sometimes a little colored, whereas predatory mites' are slightly larger, oval, and translucent. If Spical's has done a good job, you should hardly see any spider mite eggs. The standard advice is to check the status twice a week. But of course, in acute situations, it can't hurt to do more checks until you're sure the matter is under control.