Hi and welcome
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ANYTIME you suspect an insect bite/sting - you absolutely want to give Benadryl ASAP - at 2mg/pound. In my doggie ER kit, I keep the pills cut-up into the right size AND I always have liquid Benadryl on hand in case I have to force giving it (if the mouth/throat were starting to swell!).
Benadryl can literally save lives when it comes to histamine reactions from stings. So most def keep this on hand at all times - and give immediately even if unsure if it was a bite.