The Venom of Argus — Edmund Cooper

The Expendables had struck it lucky at last. After grappling with the revolting Death Worms of Kratos, the deadly Rings of Tantalus and the weirdly anachronistic military society of Zelos, their fourth mission looked an easy one. Argus was an earth-type planet with one major continent, comfortably covered with vegetation.

But that was before The Expendables encountered the deadly harpoon tree, or the low-lying plant which grasped greedily at anyone who dared to set foot on it, or the hornets that paralyzed their victims - so as to enjoy their food in peace. Worst of all the lurking horrors of Argus was the deadly hallucinogenic pollen which turned quiet Santa Maria crew members into vicious maniacs.