Buglife said not much was known about the horrid ground-weaver spider because of its scarcity.
The invertebrate experts described them as dwarf money spiders with bodies measuring 0.12in (3mm) and hairy legs which inspired their name since the Latin origin of the word ‘horrid’ is ‘bristly’.
They said the spider had been discovered as new to science in 1989 by RA Stevens.
The charity’s head of operations Andrew Whitehouse said the council had an “international responsibility to do everything that it can to protect its habitat”.
A Plymouth City Council spokesman said it was in “direct discussions with the landowner to remind them of their responsibilities under planning law”.