Someone is chomping on the leaves.

Must investigate top & underside, day and night.

The damage is minimal and on a blackberry a few less than perfect leaves don't matter at all. Ants will not harm them so no need to ' treat'. The only parts you need worry about are the flowers and subsequent fruit. Insecticides could kill pollinators and you don't want that. Btw spider mites are extremely small, almost impossible to see, so you had a spider. A good thing.

with no insult to the flower itself .. in my MI.. that looks like minimal spring cold damage to leaves.. a few weeks back ....

always mention where you are .... big city name ...

was there a cold event after leaf out???

as to the holes.. if there is a brown dried edge ... the bug is long gone.. you need to look for fresh damage.. then look for the bug ...

ken

Haven't used any sort of insecticide just a little food grade DE around the base.

I am in Phoenix, Az. Weather is fairly mild right now, although we've had quite a bit of rain the last few weekends and nighttime temps would've been between 35-50 F

minor damage to a leaf.. can take weeks to 'show'.. and 35 could have been cold enough ...

ken