Largest source of calories while surviving in wilderness

As for the original question I have two strategies for harvesting calories:

First, having done some fur trapping in the past I would stick with trapping.  Several of the earlier posts mentioned crayfish as an easily caught food.  Once you have have eaten what you can the shells will still retain the smell of the meat.  Crayfish are a favorite food of raccoons.  So, I would use any scraps as bait.  A raccoon will yeild a few pounds of meat and also a generous layer of fat.  They sometimes run in packs so you might be able to harvest them over some period of time.

I have no experience with this one and it would only work in late summer.  I had been told some of the Plains Indians would go out on the Prairie and start a small fire in a pit.  When the fire had burned down to some hot coals.  Several people would walk some distance away and begin walking a spiral path back to the fire pit. As they walked the grasshoppers would jump out of the way.  As they aproached the fire pit more grass hoppers would be fleeing in front of them. When they got close enough, the fire pit would be covered trapping many of the grass hoppers  in the pit where they would be roasted.

^^concerning grasshoppers, if you know where to find them, or where they usually are, go for them in the early morning, when it's the coldest, then they practically don't move (because of the cold), and you can just pick them. (That's actually what the hunters-gatherers were most likely to gather, some scientists believe).
For sure meat and fish (and maybe grubs) are the best way to get your calories. And learn to eat most of the animal, not only because you'll get more out of it, but also nutrition wise, you'll keep stronger and get all kinds of important nutrients then if you just would eat muscle meat.
I once heard about the possibility to eat pine needles... honestly, I would not consider this as a serious option. Maybe for the psychological effect (feeling less hunger maybe ?), but I would say in the long run even more damaging that eating nothing, because there is a lot of anti-nutrients there. Same for many wild plants and roots and mushrooms: eat with care and in small amounts only.

I believe pine needles are mainly used for vitamin C to prevent scurvy.

^^good point, but there are recipes in fashionables cook books out there from people who see this as something "new" and trendy, and who know nothing about really being in the wilderness. They want to substitute greens for pine needles in some recipes, and I am not talking about tiny amounts. No joke. And, in many of the recipes, this pine needles are to be cooked, and so the vitalmin C looses it's effect. They actually don't know that pine needles are used for that purpose.

And another thing, if you eat pine needles to prevent scurvy, you should not eat big amounts, because even though it can help with the vitamin C, it will have some side effects. Just because the ingredient is natural does not mean it's optimal for us. Anti-nutrients can be very harmful, specially in bigger amounts or if taken during longer periods of time.

Pine needles are not food, just a supplement.
Very few animals have pine needles as a primary part of their diet. They have a very low caloric content, and are difficult to digest. This makes them not effective as a food source - you need to invest a lot of the energy you get from them in digesting them... Also they are both bitter and very acidic.

Did anyone mention wild honey or termite nests?

The nectar out of flowers is also good.

That would cover 'quick' energy and protein. Fat lizards, frogs and fish also provide protein and fat - 'slow' energy sources.

Pine needles are used to make tea.  I've only heard of white pine being used,  but i dont know if others work  as well. The trees contains large amounts of vitamin c. I wouldn't try to use them aa source of calories.

F Agricola wrote:Did anyone mention wild honey or termite nests?

The nectar out of flowers is also good.

That would cover 'quick' energy and protein. Fat lizards, frogs and fish also provide protein and fat - 'slow' energy sources.

Excellent suggestions, thanks. In Thailand in remote areas I saw quite a few times people hunting for small (but fat) lizards. Another tasty treat, are bee larvae, still in the comb. Quite a lot of fat, and with honey around, a nice treat, but probably maybe not so easy to find/get.
Fat is something we take for granted, but in the wild, it is not plentiful. Wild meat is usually lean, so you would need to eat marrow, or kidney fat (and there found only in small quantities). Eggs have good fats, but maybe not always easy to find.

https://www.youtube.com/watch?v=Z7Z0essRI8E

Ray Mears "Wild food" looks at what hunter gatherers in the UK were likely to be eating, interesting viewing. the link is episode 2 as 1 is in australia.

Sea food that can't run away and doesn't require digging up, snails, frogs other small animals would be my choices, combined with roots and leaves. berries/nuts in season.