The Tholians are very territorial and pose the Federation a threat. They have done so for over a hundred years.
Their physiology is different then that of humans. They are primarily reddish in color. They exist at over 178°C or 350°F. They could exist at lower temperatures for brief periods. Severe cold temperatures would cause them to crack and die.
Their immune system could eventually repel some toxins. They emit various forms of radiation. They could communicate short-range this way. They communicated with clicks and chirps.
Their goods are often hard to get. Tholian silk is highly treasured but not easily able to be acquired. High prices and low availability are the reasons for this.
There are known for their quick tempers. They are quick to use force. They annex areas in around their own space.
Their ships could span webs trapping other ships in it. In the late 2260s, they could disable a Constitution Class ship with the conventional beam weapons.
The Tholians would destroy a Federation starbase in 2353. The only survivor would be Kyle Riker.
In 2371, it appeared that peace may take place between the Federation and Tholians. This peace conference was bombed and the Tholians would go on and sign a non-aggression peace treaty with the Dominon.