Dock workers at the Port of Guam have criticised port officials for failing to ensure their safety after a ship docked infested with black widow spiders.

Workers claim management mishandled the situation by allowing fumigation to take place at the dockside, instead of sending the ship back out to sea.

Guam Federation of Teachers Union President, Tim Fedenko, said workers are still finding the venomous spiders at the port and in their homes.

Sorry, this audio has expired Black widow spiders invade Port of Guam ( Richard Ewart )

"We do know the port workers had to offload and continue working equipment while the ships were being fumigated," Mr Fedenko told Pacific Beat.

"They were fumigating at the back with the gang plank down. So there were confirmed spiders on the dock.

"[Workers] said there's been one in the [port] bathroom and one guy said he found one in his backpack when he went home."

Spiders 'could damage environment'

Mr Fedenko said the potentially deadly spiders could damage the island's ecosystem.

Hopefully they're still just in the port, and a greater fumigation can take place, but invasive species are very, very tricky," he said.

"It's a very sad situation for Guam ... we've had problems with invasive species in the '70s.

"After World War Two we had a problem of invasive species of the brown tree snake, which has pretty much decimated every bird off the island... they've definitely messed up the ecosystem."

The ABC has contacted the port for a response.