Spiders are to blame for Toyota's massive recall of more than 800,000 vehicles last week.

This isn't some Halloween prank. The critters have been spinning cobwebs and making their homes in tubes in the cars' air-conditioning units and causing all sorts of problems.

"Spiders have been implicated in the condition," said Cindy Knight, public affairs manager for Toyota. "It's a very rare occurrence, but a spider can get into the air conditioning drainage tube and build a nest."

Those nets were blocking drainage in the tubes, which led to leaks. In some cases, these leaks drained on top of the airbag control units in the vehicles, causing electrical short circuits and airbag malfunctions.

Toyota announced the recall last Thursday, but Gwen Pearson of Wired was the first to report the spider's contribution to the problem in this fascinating piece. "This makes sense to me, as a spider-watcher," she wrote. "It's warm under a car, it's dark, it's damp -– it's the perfect spider habitat."

Two people sustained what Toyota described as "minor" injuries in accidents when their airbags failed to deploy because of this problem, which has affected the 2012 and 2013 Camry, Camry Hybrid, Avalon, Avalon Hybrid and Venza.

"The remedy," Knight said, "is to help prevent water from the condenser unit housing from seeping onto the airbag control module."

Airbag-related malfunctions have caused increased problems for automakers this year. They've issued 29 airbag-related recalls so far in 2013, which is a record. Toyota has recalled vehicles for airbag problems four times, and three of the four have recalled more than 800,000 vehicles.

Across the industry, those are the three largest airbag recalls this year.

This isn't the first time spiders have caused problems that resulted in a recall. In 2011, Mazda had to recall 65,000 cars because spiders nested in hoses attached to the fuel system. This dude sent his car to be painted, and it came back with a nest filled with freaky spiders. So he did the natural thing -- took a video and put it on YouTube. Of course.

It's not uncommon for critters to take residence in cars. One woman had an ant infestation. Rabbits caused a huge ruckus at the Denver International Airport after they were caught chewing on car wiring in the long-term parking lot. And one terrified family drove down the highway with a snake flapping around on the windshield.

Pearson notes the greater problem with spiders and automobiles usually isn't found under the hood. It's when drivers see spiders, get frightened and get distracted. "Mechanical problems related to spiders are extremely rare, as best I can tell," she says. "The primary way that spiders cause problems in cars is by making people freak out."

Indeed, a spider spooked a driver in Cornplanter Township, Pa., last month, causing a one-car crash in which two occupants were unhurt. In 2009, an accident occurred when a bug landed on the back of a truck driver in North Dakota. He overturned, but his load of "rocket engine parts for intercontinental ballistic missiles" was nonetheless safe, according to reports.

Pete Bigelow is an associate editor at AOL Autos. He can be reached via email at peter.bigelow@teamaol.com and followed on Twitter @PeterCBigelow.