could be it...i saw a fire ant fall into my guppy tank and saw a guppy eat it eat...within an hour or so...there was a dead guppy in the tank. didnt know that there were toxins in fire ants...
sorry again for the loss and glad you found the insect in there!
this may be a weird question, but do you have cats? i have 3 and mine love to drink out of my tanks; weve been discouraging this behavior. i am concerned maybe mine would introduce something (primarily ammonia) to a tank since they dip their paws in to drink. just a thought and so sorry about your loss
i remember reading once about a guy who had a £2,000 marine fish which spat at flies and eat them. open top ov course. the fish spat at a wasp caught it and eaten it then died off......OUCH!!!