The Tom & Jerry Show (1975)

It's No Picnic (1x46)

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Disaster occurs at an insect labatory, when an ant gets ahold of a growing serum. The ant breaks out of the lab, and goes on an eating rampage. It runs into Tom and Jerry, who are having a pleasant picnic. After panicking, they calm down, and think of numerous ways to get the ant back to its original size, before the ant causes anymore damage to the town.