Well, I think it is safe to say that the Splerions own the best biosensors of this universe :)
The universe is so vast that I can only imagine the type of range they would have on their spacecraft's sensors to be able to detect other far away beings.
I liked the clogging system as an evasion mechanism. I believe the Splerions would need to return home for some cleaning (probably flying on some remote control system, since the main orientation mechanism would be obsolete). This would probably buy other victims enough time to travel safely (if most of Splerions' spacecraft were to be affected).

One interesting strategy would be to attract them and blast them with the clogging chemicals. Basically, neutralize them for a good period of time.
Interesting to see that even the most powerful systems, also have exploitable weaknesses.

As for the humans attitude, I bet they were threatened in order to comply with the Splerions. Let's see!

Looking forward for the next chapters!
Thanks for sharing!