Symbiotic Relationship between Spider and Fly

This symbiotic arrangement between these two individuals of separate species is not normal and cannot be considered to be instinctive, hereditary or genetically induced.

I do agree that most of a bug's behaviour is sufficiently repetitive to be stored genetically and its life functions do not have to be learned; walking, flying, mating, nest building, food collection etc. are all automatic knowledge. However, decisions still have to be made.

In the case of this symbiotic relationship, a considerable thought process had to occur on both sides:

Fly – the spider is dangerous and wants to eat me. I can sense surplus food that the spider is not consuming. If I show cautious interest in the excess food, will the spider grant me access?

Spider – there excess food on my fangs that I cannot remove. The fly is a small meal, but I have just eaten and do not require food. The fly shows interest in my excess food problem, should I grant access?

The above thought process must take place on both sides for the natural instinct of both species to be overwritten. This is clear proof that bugs are capable of complex thought processes.

Location is Bandung, West Java, Indonesia. Alongside a stream and paddy fields.