Tag: carpenter ant

Bears: Connoisseurs of Rotten Wood

Late summer is upon us, and along with the fruits and nuts that are ripening everywhere, insects are becoming more available. Insects are an important part of the late summer diet for black bears, and the animals seek out insect populations that are abundant and easily obtained. Decaying stumps, rotting logs, and standing dead trees often harbor large numbers of grubs, ants, and other invertebrates. With their highly developed sense of smell, bears can detect these creatures even when they’re hidden deep inside rotting wood. But if they’re protected inside wood, how easy is it for a bear to get at the goodies?

Just check out the photo below, which shows a tree that was ripped apart by a bear. Large pieces of wood lie scattered around, and the inner parts are broken up and exposed. Only a bear would have been powerful enough to pull a tree apart this way. Notice how the fragments were tossed in several different directions and how some lie quite far from the base of the tree.

Logs on the ground also harbor populations of insects. The next photo shows similar signs of bear activity: large fragments tossed to considerable distances.

Stumps may hide the same kinds of food as logs and whole trees, and bears tear into them in the same way. In the next photo you see large pieces of wood that were pulled away from the stump, some tossed impressive distances. Again, this is something that only a bear could accomplish.

A bear wouldn’t exert this kind of effort if there weren’t something really good–and abundant–inside, and very often it’s the fat- and protein-rich larvae of carpenter ants or wood-boring beetles. The holes and galleries you see in the next photo (a close-up of one of the fragments from the tree in the first image) could have been made by either. It’s often difficult to know what was occupying the wood before the bear tore it apart, because everything edible has been eaten and other clues–like frass–have been washed or blown away.

Bears aren’t the only agents that cause trees and logs to come apart. We usually think of woodpecker excavations as occurring on standing trees, but it’s common for birds to open up logs on the ground. Pileated woodpeckers can do quite a job on a log, as shown in the next photo. But notice the differences: there aren’t any really large fragments, and most of the scattered pieces are quite small and close to the log.

Logs can also disintegrate without any help from animals or birds. The log in the next photo fell apart of its own accord. If you look carefully you’ll see that there’s an order to the way the pieces are arranged. The ones that were originally on the surface (one with bark and another with moss) lie at the lower left. A little above those there are chunks that were originally in the interior of the log. With a little imagination you can reassemble the fragments as they were before they fell apart, and picture the way they collapsed from the main part of the log and landed where they did.

Sometimes the goodies lie underneath rather than inside a log. The photo below shows a log section that may have sheltered an ant nest. Again, only a bear could have moved such a massive hunk of wood.

It’s surprisingly uncommon to find claw or bite marks in the wood, but recently I came across an interesting exception. The log in the photo below showed the usual signs of bear work: sizable chunks of wood tossed far from their source. But there were also unmistakable claw marks.

A close-up of the log can be seen in the next photo. What the bear was after must have been in the cavity in the center of the photo, and in the wood above it you can see claw marks. There’s a clear set of five gouges on the right and another less well defined group just to the left. The animal must have stood roughly where the camera was positioned and raked its claws downward. The wood was rather tough, but the bear was able to rip off large sections. I didn’t find holes or galleries in the wood, but there was some finely divided granular material in the cavity, which suggests an ant nest.

Bears open up trees, logs, and stumps during late summer and early fall, when insect populations are highest and grubs and larvae are fat and abundant. The foods they find in rotten wood, along with the calorie-rich fruits and nuts of late summer, allow bears to put on weight and survive winter hibernation. Every time I find a log, tree, or stump that was opened up by a bear I appreciate the animal’s strength and dexterity, and imagine how it relished the tasty (to the bear) items it found inside.

Black Bear Days

Black bears habitually cover great distances in search of food, moving from one source of edible treasure to another throughout summer and fall. The animals often find our trails and primitive roads to be convenient travel routes, and the muddy spots that develop in rainy weather are an ideal medium for capturing their tracks. I recently found these tracks on a forest trail used by snowmobiles and ATVs. The direction of travel is to the left; the left rear print is at the lower left and the left front is at the upper right. Bear tracks, especially those of the hind feet, may remind you of barefoot human tracks, but beware–the largest toe lies on the outside of a bear’s foot rather than on the inside.

But even when there’s no mud, you can learn a lot about the daily lives of bears by observing the sign they leave. Bears love fruits of all kinds. The bear that climbed the shadbush trees pictured below probably knew they wouldn’t support its weight. But no matter, it was easier to eat the berries while standing on the ground anyway.

When apples start to ripen, bears climb the trees to get to the sweet fruits in the highest branches. The gouges in the photo below show how the bear’s claws slipped downward before they caught firmly enough for the animal to move farther upward. When feeding on apples or other fruit, bears sometimes break branches and leave them hanging in the tree or on the ground below. Smaller animals like raccoons and gray foxes also climb trees in search of fruit, but their claw marks are narrower and do not show the separation distances of one inch or more that are typical of adult bears.

Insects are a much sought-after source of protein, and bears dig up nests and tear open logs and stumps to get at grubs and larvae. Even whole tree trunks are not too much for a bear’s power. The snag in the photo below was dismembered by a bear. No other animal would have been able to break out the large sections of wood and scatter the fragments in several directions.

It’s not always possible to determine exactly what a bear was after, but in the case of the tree above the evidence–the remains of carpenter ant galleries shown in the photo below–was still present in the large wood sections. Carpenter ants don’t actually eat wood. Instead they use trees as nest sites, and the tunnels and galleries they create in dead wood serve to house their eggs and larvae. Once an ant nest is exposed by a marauding bear the adult ants flee, but the eggs and larvae, and probably a fair amount of wood, are scooped up and consumed en masse.

Bears are also concerned with the movements of other bears, and they keep tabs on each other through various kinds of messages. The bites which decorate the balsam fir shown below were made by a bear standing on its hind legs. To leave such marks a bear sets an upper canine tooth in the bark and draws the lower canine in. This leaves dot-dash patterns like those to the left of the debarked area. The debarked area itself resulted from repeated biting, and the weathered appearance of the exposed wood tells us that the marking had been going on for a number of years when the photo was taken. Such marks may be visible to bears at close range, but more importantly, they hold the scent of the animal which made them, and bears are famous for their keen sense of smell.

This was a large tree, and it must have been a magnet for every passing bear. It stood about twenty feet off of a seldom-used hiking trail, and between the trail and the fir tree there was a narrow passage with distinct step spots. These step spots were created when approaching bears walked toward the tree with an exaggerated swagger, planting each foot deliberately as if they wanted to leave as much evidence of their visit as possible. In the photo below the step spots show as brown areas of bared soil.

Bear sign, and sometimes tracks, can be very abundant, but unless there’s an artificial attractant (such as garbage or handouts) they’re seldom seen. But fortunately for us their strength and resourcefulness can be observed in their tracks and sign. We can even read, albeit on an elementary level, their messages to each other.