That's a great example for the search quality team. What's interesting is the synonym "insect"="bug". Note that the result you like is whatsthatBUG.com, which actually contains no instances of the original query term "insect" and only two isolated side navigation instances of "insects".

Yet it seems like the synonym "bug" on Google, plus the other terms like "junk" and "attached", leads to complaints about software.

In a way, you were lucky that the whatsthatbug.com result actually had the word "junk" and "attached". The letter-writer was using the word "junk" in the same meaning you were, but they were using "attached" in the phrase "see attached pics", whereas you were referring to the debris attached to the insect's back.

We're working hard on improving these kinds of challenging queries. I'm going to be remembering the insect with junk attached to its back for a while!