That is common in a lot of cases. If there is a mass amount of bugs that a bigger bug feeds on, it's like a non-stop buffet for them, so they stay and eat their faces off.

Ladybugs also help as well. Every summer I get a spider problem. They (try) to infest my entire garden, laying blue, fuzzy sacks of thousands of them everywhere. I found a ladybug one day and put it on one of plants. That ladybug stayed there for a good 4 or 5 weeks, spider free. I was watching that fucker one day and all it did was roam the plant, over and over again. Not harming the plant, but killing off anything that tried too.

Some bugs are good for a lot of reasons, except misquitos. Why do they exist? They suck!