It's what's known as a bioluminescent burglar alarm, and just like the alarm on your car or your house, it's meant to cast unwanted attention onto the intruder, thereby either leading to his capture or scaring him away.
I poput alarma u vašem autu ili u vašoj kući, uloga mu je da baci neželjenu pozornost na uljeza, vodeći do njegovog ulova ili do zastrašivanja.