Welcome to the forum Whispering Giant. They may well have been crickets if the area was warm, damp and dark.
I did a lot of work in boiler houses at factories in the 70’s you could guarantee that in any dark corners or in the service ducts/pits there would be crickets and because of the warm, damp environment and lack of predators they grew very large. I suppose like most insects they will take on the colour of there surroundings in some cases.
There was also a story that was told to new lads joining us to watch out for the Steam Bugs when removing lagging from steam pipes. They were reputed to be so large that they could carry your heavy tools for you.
I never saw a Steam Bug but saw plenty of Crickets.
When I worked a Bakelite, they had a Bug Farm, The bugs would convert toxic waste to something less toxic. These bugs though were microscopic.