When the corpses of these creatures were found they were
named "Roaches". This name has stuck. The rest of the
"information" we have on them is mainly conjecture. We
summarise this:

It has been theorised that these creatures and terrestrial
insects may share a common ancestor. Their form was a direct
consequence of the unpleasant conditions upon the Sirian
planet on which they evolved. Their physical form impaired
their ability to develop and use technology. If this had not
been the case, the whole Galaxy would probably be over-
run by these insects.

The Sirian Creatures are ancient by terrestrial standards.
There is reason to suspect that the present evolutionary form
of these creatures was achieved while dinosaurs were the
highest form of life on Earth.
Like terrestrial insects - as individuals each creature is
quite stupid and powerless. They act as large communities
directed by queens.

However, unlike terrestrial insects, they do not communicate
using chemical scents and tastes.
The bodies of "roaches" contain metallic particles which act
as organic radio transmitters and receivers. In other words,
these insects are naturally telepathic. It is this ability
which not only allows them to communicate but to combine
their limited intellect to form a group-mind.
They have a shared consciousness. Groups of tens, or even
hundreds of insects are needed before any true intelligent
behaviour is demonstrated.
It can be argued that the entire Sirian-League is a single vast
creature - rather than a collection of individuals.