Can't say I ever wondered how many calories I'd burn digging worms, but that didn't stop me from being amused to find that very activity in the bible of energy expenditure, The Compendium of Physical Activities Tracking Guide.
So, digging worms, with shovel? That's a 4.0 MET activity.
What's a MET?
It stands for metabolic equivalent of task, and the easiest way to define it is as a reference, where 1.0 METs is the energy required to laze around doing nothing. Worm digging with a shovel therefore, takes 4x the energy required to lie around.
Actual calories burned will vary based on many factors, though a rough generalization would be that a 1.0 MET activity would burn 1kcal/kg/hr. Laze around for an hour, and if you're a 72kg guy like me, you'll burn 72kcal doing so.
A great many folks trying to lose weight keep track of the calories they burn exercising. Often they'll use them as negative calories whereby they'll subtract them from the calories they've consumed to give a net total.
Unless you're a truly hardcore record keeper or exerciser, I don't think that's the greatest plan.
Reason being is that record keeping is fraught with error.
I'd look at your exercise as being a means to buffer your error, not as a means to lower your count. Only exceptions there would be incredibly accurate record keepers, or folks who were exercising significant amounts.
The exercising folks, it's not that I'd want them to calculate net calories, just that I think it's important, if exercising for more than 45mins, to fuel properly so as to minimize the potential impact of exercise on hunger.
Oh, and in case you were wondering, that same bible notes caulking or chinking a log cabin as a 5.0 MET activity.
Playing the accordion? 1.8. Bookbinding? 2.3 Horse grooming? 6.0. Pushing a plane in and out of a hanger (huh?)? 6.0, and SCUBA diving as a navy frogman? 12.0.