Every time I read about genetic engineering and pests, I remember this old chestnut from the simpsons

SKINNER: Well, I was wrong. The lizards are a godsend.

LISA: But isn't that a bit short-sighted? What happens when we're overrun by lizards?

SKINNER: No problem. We simply unleash wave after wave of Chinese needle snakes. They'll wipe out the lizards.

LISA: But aren't the snakes even worse?

SKINNER: Yes, but we're prepared for that. We've lined up a fabulous type of gorilla that thrives on snake meat.

LISA: But then we're stuck with gorillas!

SKINNER: No, that's the beautiful part. When wintertime rolls around, the gorillas simply freeze to death.

if only they could be modified to inject something useful.