There are many ways to go about it. First, the earlier the better. The more used you are to daily tapping, the faster you'll think of it, the stronger the effect.

Physical symptoms.
You can tap on the instant of the sting:

Even though I could feel the sting, but it was too late, I deeply love and accept myself.
Even though it was soooo painful, and I'll have this for a few days...

But I'd suggest to tap on what you feel right now

Even though I have the scratchy sensation on my arm, ...

The feelings about the moment of the sting... and the future
What was happening at the very minute of the sting or bite? Were you already in a “bad mood”? Why? You might have seen the insect, tried to chase it away, unsuccessfully apparently! That could make you slightly angry at the culprit (or at yourself?):

Even though I could see it coming, this thing was after me, I know it was targeting me...
Even though I'm furious, it doesn't really make it any easier at all, what if I let the anger go? I wonder if the sting would be easier to cope with?

You might have taken some kind of inconsiderate risk.

Even though I was so stupid to walk there, no wonder it stung me....

You might have been taken completely by surprise:

Even though I didn't see it coming, and I should have...

The more annoyed you get, the more difficulty your system will have to cope with it. It might be a good idea to consider the point of view of... the insect! And put in a little forgiveness for it, for you?

Even though it's unfair I got stung, this insect reacted according to its nature.....

Also, tap away your anxieties about the coming days. In most cases, your body will need a few days to eliminate the venom, but until then, it WILL be painful (or will it? ;0)

Even though I”ll have to walk around with an arm like Popeye....
Even though I will have to restrain from scratching my leg....

The possibilities are endless. Most of all, be persistent about it.

I had various results about this for myself, including times when it didn't really “work”, I think just because I got fed up with tapping, and decided I'd live with it. Yes, even I rebel against tapping some times when the resultas are not fast enough! But it can be worth spending 15 minutes to save 3-4 days of itching?

On the other hand a visiting friend stepped on a wasps nest in the woods and got 9 stings as a result. He chose to tap, as well as using cream on the stings. We tapped for about an hour. Considering that he had an history of allergy for 2 bites as a child, and that he was on anti-histamines, the result was quite impressive. He found that it removed all his fear of the possible reactions. It was itchy for a couple of days, but he could tap it away if it was too annoying, and the swelling was minimal. Interestingly enough he mentioned that the 2 bites on his arm, the most visible, which he was watching closely as we were tapping, healed faster and were even less swollen than the others. All of them disappeared faster than for a (non tapping) neighbour who had been stung a day before him and felt the pain for many days after him.

So see where your tapping takes you.
Please remember to ALWAYS consult the appropriate specialist for ANY medical condition. While tapping has been shown to help with this, remember EFT is NOT a medical procedure. But pending the medical treatment, or in support of it, you can certainly tap!

Clic here for a free tapping script that might help you.