If spring is marked by the return of life to our somnolescent winter woods, then the flow of sap is really that first and most prominent signifier that spring is here! When I tapped trees with kids out at the Field School, I had one rule: No Sugar Maples. All trees have sap, even conifers, and many of them produce delicious sap that can be tapped in much the same way as sugar maple. And so it became an experiment to find new flavors, to figure out which trees have sap that floweth freely and when this sap flows. We took inspiration from yellow-bellied sapsuckers, which tap and eat sap from at least 174 different species across their range (more on how sapsuckers survive winter). Some species were a total bust and had no sap flow (e.g. musclewood, apples, black locust, tamarack, etc.). But some were incredibly delicious. Black walnut with its rich carmel-y flavor was easily my favorite, though I also enjoyed the birches.
Animals are similar cued into the spring sap flow, and a variety of animals will consume the sap from damaged trees. However, it’s surprisingly rare for animals to actively create holes on a tree in order to directly consume either xylem sap (sugars, minerals, hormones that flow from the roots to the leaves) or phloem sap (sugars, minerals, hormones as well, but usually different ones that flow from where the sugars are produced to where they’re stored and/or consumed).
Insects: phloem sap feeding is restricted in the insect world to just the Hemipterans (an order that includes true bugs, aphids, planthoppers, cicadas, scales, shield bugs, etc – source.) and xylem sap feeding isn’t all that much more widespread (source). Most of these insects have long probosces (like the sucking mouthpart of a mosquito) and go after younger tissues or trees with thin bark (like beech scales, the vector for Beech Bark Disease).
Birds: It’s primarily woodpeckers (downy, hairy, acorn, etc. – source) that create holes to feed on sap. Of the bunch, sapsuckers are easily the most reliant on sap (there holes are always in horizontal rows, as in the photo above). Other birds (like hummingbirds) will steal sap from sapsucker tap holes and have to defend these. While hemlock is one of the most frequently tapped trees by sapsuckers, I’ve never been able to extract any sap from it.
Mammals: In mammals, it’s mostly squirrels that eat sap (bats and porcupines have also been observed feeding on sap). And I’ve seen both red and gray chew branches to create tap holes and then return to these repeatedly to lick up the sap.