This pet ends up being used for biological warfare, in a way.
After Kevin accidentally unleashes Buzz's tarantula, it goes scurrying around the house. As Kevin prepares his booby traps in a montage, we see different shots of the spider crawling near the traps. It's a great example of foreshadowing—we know something's going to happen with this spider, but we just don't know what…
Finally, as Marv almost captures Kevin, Kevin spots the tarantula and grabs it, putting it on Marv's face. Marv screams and the tarantula crawls across Harry, who Marv hits with a crowbar while trying to kill the tarantula.
Fortunately for all arachnophiles, the tarantula escapes. We're left wondering—maybe this spider will go crawling across Buzz's face, sometime soon? (We can only hope.)