p_p
I am going to guess you have one of the candy colored all-in-one CRT (tube-type monitor) encased in a plastic case - and that bug(s) have gotten inside the case between the CRT and the clear plastic part of the case??. (skydiver?)
EDIT
Can't remember nor tell from the image whether
there is plastic in front of the CRT glass. 😕
Not being an service-person nor an exterminator, I cannot advise - perhaps someone could point you to the appropriate dis-assembly instructions if you would state your exact model of Vintage iMac - or maybe a DIY exterminator might offer a non-invasive method for poisoning the critters 👿
CCC