I know when it's fresh, nail polish remover can help. After the washer and dryer, though, I'm not sure if it will work.

It really is dried glue. Applied heat should make the resin run again, at which point, you might be able to wick it away. If the shorts can be washed in hot water, try letting them soak in boiling water. The sap should run and float to the top (you may have to stir with something heat resistant). If the pants can't take that kind of heat all over, maybe try a hot hair drier held an inch or two from the spot, then dab with a disposable cloth.

To the tune of "The Sign":

I sat in sap
And I can't clean off this crap
I sat in sap

Nothing seems to do the trick
Got a stain on my butt that don't belong

Sap that I sat in,
Nearly reaching my end ...

Such is the sap that kisses your ass
A quote stolen from your colon
Says this too shall pass.

i linked stain removal pages here before but it bet they are googlable.

If, as IRFH suggests, heating it will make the sap treatable, and if the shorts can take some heat, there's a simple method that might work: you lay absorbent cloth (thick layers of paper towel would work, even) on each side of the stain and gently move a warm iron over the affected area. I've used that to remove wax and, once, glue, but never had to try it with sap. It might work.

If.

IANAL*.

*I am not a laundress.

ALLOW ME TO LICK IT OFF!

I'm also not a laundress. And I can't vouch for the material or the chemical affect of laundry detergent. But I do know that many saps and resins are used as common glues, that they are prepared in their most basic form by simple heating, and that untreated, they can be reheated back into liquid form almost indefinitely.

Yeah, IRFH, I didn't mean to impugn your advice. (Oh, no, an impugning!) Heating it seems like a sensible way to attack sap, and I wish I'd thought of it when I got sap on my favorite linen skirt. (I was crouched around an enormous pine tree showing an enormous colony of spiders to, er, an enormous colony of children. They --- the children, not the spiders --- loved it. It was worth getting sap all over my favorite skirt.)

I typed up my comment, realized I sounded quite certain, so I added the oh-so-comic "if"s to clarify, without realizing it sounded like "Harrumph, IF the gentleman knows what he's talking about..." My, as the youngsters say, bad.

My dear sir, I would never harrumph at you.

[Am totally picturing IRFH in a laundress' mobcap, a washtub and scrubboard at hand.]

"I sat in sap."

Ooh, sticky buns!

At no moment did I feel impugned. You just reminded me that I should qualify that my answer was based on knowledge of the properties of sap, not cotton/nylon blends. Although I do wash a mean load of laundry now and again.

One must go to the master for such things.

Few things to try, now, thanks!

*runs from quonsar*

[Am totally picturing IRFH in a laundress' mobcap, a washtub and scrubboard at hand.]

Dame Washalot, up the Faraway Tree.