In Ecuador, two reckless money-hungry pilots bribe officials to fly a load of coffee beans into the United States, secretly smuggling three passengers aboard to help pay off their scheme. As the cargo sails north, trouble brews when sacks of beans conceal deadly tarantulas, and a fierce thunderstorm tips the balance—the arachnids break free just as the plane is unsettled by the weather. The three illegal immigrants are trapped in the cargo hold, fighting the spiders with whatever they can find, including shoes and improvised swatters, but the relentless creatures overpower them in the cramped darkness.
In the cockpit, the pilots confront a developing mechanical problem and must execute an emergency landing as they skim over Finleyville, California. Unbeknownst to them, the tarantulas have already escaped into the plane and begin to swarm the cockpit, contributing to the disaster when the craft touches down near Finleyville.
Back on the ground, Finleyville’s emergency teams rush to the wreckage, and a fire erupts at the crash site as the deadly intruders start to spill toward an adjacent orange grove. The fortunate survivors are pulled from the wreckage, yet many begin to exhibit alarming symptoms, confounding the town’s medical community. Dr. Hodgins, [Pat Hingle], struggles to diagnose the unfolding mystery as a bitten bystander suddenly collapses and breaks into old vaudeville songs.
Cindy Beck, [Deborah Winters], and her fiancé Joe Harmon, [Charles Frank], join the effort to untangle the occurrence, while Cindy’s brother Matthew, [Matthew Labyorteaux], discovers a spider and tries to sound the alarm, though his warnings initially fall on deaf ears.
A determined Beck family teaches the town how little is known and how much there is to fear. They learn that the intruders are banana spiders, described with chilling simplicity as, > "the most aggressive and venomous spider in the world".
Mayor Douglas, [Bert Remsen], and Bert Springer, [Claude Akins], rally the community to confront the growing danger as the spiders begin to threaten the town’s livelihood and its people. The bite of another family member proves fatal, underscoring the urgency of finding a cure or a control strategy.
The groaning problem forces a drastic plan: using the buzzing sounds of wasps to disorient the tarantulas, enabling a crew to capture the spiders in buckets of alcohol that kill them. An electrical outage complicates the operation, leaving the team briefly surrounded by the advancing hordes until doors reopen. A resourceful local teacher, [Nancy Burnett], crawls through a window near the roof to guide everyone to safety. When power returns, the town races to finish removing the remaining spiders and protect the area around the orange packaging plant, hoping to prevent a wider disaster.