In the scene where the Predator examines the dead Scorpion, it is using heat vision, and you can see the Scorpion's body heat escaping once its dead. I applaud the creator's efforts to show this, most films won't go this far for detail, but the creators missed something. Scorpions do not have body heat.
1. Scorpions are arachnids, which in reality are cold-blooded. Do not take this literally, it has little to with their blood and body heat, it has more to with the amount of chambers their heart has. A crocodile is cold-blooded, but it still has its own interior body temperature under the protective skin. But a scorpion does not, or has very little. If you put a scorpion, or a snake on ice, it will die in a matter of seconds. Because they do not have sufficient body heat, they need to live in hot places that will provide that for them.
2. Even if the scorpion had its own heat, it would have such a small amount, the Predator would not notice it. It would be camouflaged against the logs/trees/shrubs and rocks.
3. Even if it had its own heat again, it would not leave its body in such a fast time.
So, no, it never had that much noticeable heat to begin with.