Beetles in Dead Trees

It is a very common – and very worrisome – occurrence for you to find some large critters running around on your family room floor on a cold winter day, in this case “critters” who do not resemble your children or the dog. The question that may naturally come to you is “where the heck are these bugs coming from – it’s the middle of Winter!” Quite often you need look no further than your fireplace, and the stack of firewood you brought in a week or two earlier. The bugs are often the large beetles that were merrily munching on this dead wood in their role as decomposers in nature.

Here’s the scenario. A tree dies, and almost immediately many kinds of insects detect this change in the tree. Since the tree has very little use anymore, for purposes of propagating the forest or photosynthesis, the “goal” of a smooth-running environment now is to recycle all that organic material locked up in the tree. A procession of insects will be the first ones to work on this, and it begins with beetles and wasps. Yes, believe it or not, there are wasps that participate in the decomposition of dead wood, and anyone who has had one or more of the large “horntail” wasps come chewing out through the interior walls of their house is already familiar with these guys.

The beetles that normally are first on the scene will be in one of two families of beetles – the shiny, colorful Metallic Wood Boring Beetles in the family Buprestidae, and the huge Long-horned Wood Boring Beetles in the family Cerambycidae. Within these families there also are some species which may infest living trees, particularly in the branches, where they can cause damage to the tree. There also is one species, found only along the east coast of the United States, which will infest wood that is built into our homes, and this beetle is called the Old House Borer. It is the only Cerambycid which is a true threat to structural wood members. But, within this article we will discuss those species of beetles which are the decomposers, and hope it gives you insights on how to deal with them should you and they cross paths someday.

Going back to our bugs-on-the-rugs beginning, we can trace the problem back by understanding the life cycle of the beetles. The tree dies – perhaps from natural causes of disease, fire, or old age, or perhaps from humans cutting it down. Quite often orchards of almonds, cherries, or walnuts are removed to make way for other uses, and the trees are cut up and sold as valuable firewood, usually that first year. Immediately after the death of the tree the adult beetles gather on the bark, laying eggs in crevices they can find. Within a week or so the eggs hatch and the tiny larvae bore into the tree to begin their feeding and growth. The smaller species often take only a single year to complete the transition from egg to adult beetle, while some of the huge Prionus or Ergates long-horns may live for 5 or more years as the growing, developing larva. These larvae, called “round-headed borers”, eventually grow to the size of cigars, chewing holes an inch in diameter as they munch through the wood.

In South America, by the way, they are considered delicacies.

The beetles must lay their eggs on the bark of the tree, and this is the reason they simply are not going to get into your walls or furniture and become a problem after your home is built. However, it is very common for many of these beetles, as well as that Horntail Wasp we mentioned earlier, to be built into your home, and this is why they come out of the walls. When trees are milled to lumber to be used in building homes it often is not dried in any manner other than air-drying, and this process does not create conditions within the wood that will kill insects living there. In particular, if you’ve ever peeked inside the walls of your home, you realize that the 2 x 4 studs of pine or fir used there can be pretty junky wood, and since it won’t be visible wood in a finished home its appearance is not that critical. It is from these boards that beetles or wood wasps often will appear, and they will chew through whatever stands between them and the outside world as they seek the light. Sheetrock, wallpaper, paneling, or even tiled floors are not immune to the strong jaws of the exiting beetle adult.

One of the most common long-horned beetles found in homes along the West Coast is called the Nautical Borer – I have no idea where some of these common names come from. Perhaps it was first found on ships. It is about one inch long, dark gray with light marks on its wings, and when running around on your floor may closely resemble a large spider. If you see these things your best control measure is (a.) a fly swatter (b.) a vacuum cleaner, or (c.) open the door and let them out. They are harmless to you and your home, and the probable source will be firewood logs that you brought into the house a few days earlier. The Nautical Borer is a common beetle in hardwoods such as oak, and from one oak log I was given, about 8 inches in diameter and 12 inches long, I had over 50 of the beetles emerge. The adult beetle laid eggs on the wood last spring when the tree was cut down, the larvae progressed through their stages and changed to the pupa stage prior to cold weather setting in, and these pupae were then just resting in the wood waiting for the warmth of spring to trigger their change to the adult stage and emergence from the wood. You brought on that trigger of warmth by bringing the wood inside, away from the cold outdoors. The Nautical Borer absolutely will NOT infest your home.

Oh, and put the firewood back outside.

A little more worrisome are the bigger species of Long Horned Beetles, such as the genus Prionus, where the adult beetles can be over 2 inches long. There have been entomologists who found them emerging as adults seven years after they cut a piece of wood, so their life as a larva in the wood may last a long time. As the larva feeds it creates feeding channels about one inch in diameter, obviously doing some damage to the wood. Still, though, if you are the unlucky recipient of one of these beetles, emerging through the sheetrock or paneling on your wall, the best control is no control. It is very likely that you have no more in the structure, and they will not re-infest the wood. Simply sweep them out the door or vacuum them up. A few of the oddball places I have seen these beetles come from have been a pair of women’s shoes and the leg of an office desk. Again, in both cases they were in the wood before it was used in the making of the articles.

The beautiful Metallic Wood Boring beetles have similar life habits, and once they have emerged from lumber that was infested they simply will not lay their eggs back on the wood in your home. They need a log with the bark still on it. However, one nasty habit that has been observed with one of these beetles is the ability to delay their emergence for many years. In one case a home 25 years old had some of the green Buprestids come out of the walls, so they apparently went into a lengthy hibernation, probably in the pupa stage, waiting for some unknown stimulus to finally cause their change to the adult stage.

Beetles in Dead Trees

There are many species of the long-horned beetles that have been found in homes, usually from firewood. Their long legs and antennae are often the giveaways that distinguish these beetles from other kinds of critters that may find their way into the home, and perhaps give you a clue as to where to begin looking for the source of the problem. But, the one thing we should keep in mind, once we get over the horror and revulsion of having a “bug” on our carpet, is that these insects often play important and helpful roles in a smooth-running environment. Dead trees need to be recycled, and since there are no gas-driven stump grinders and branch chippers in a forest, the Recycling Crew is called in instead. A quick scenario might go like this.

A pine tree dies, from fire, disease, or perhaps the attack of bark beetles. Within only days of its death the beetles and wasps have discovered this new resource, as a home and food supply for their offspring. So, they fly to the dead tree and lay eggs on it. The eggs hatch and the tiny larvae burrow inside where they are protected, and where they will feed and live until they finally change to the pupa stage. As larvae, they may feed in there for anywhere from one to over seven years, grinding their channels through the sound wood inside the tree, finally moving to the area just under the bark. There they create a small chamber in which they pupate, and then wait until the outside conditions are just right for survival in the outside world, and they chew a hole through the bark and emerge as new adult bugs.

If the tree is still appropriate for their kind to feed on these adults may lay their own eggs on the bark and another generation of beetles chews away at the wood. Or, as is more likely, the next group moves in, perhaps carpenter ants that find the exit holes of the beetles and enter the tree trunk, where they create larger chambers in which to create their colony of queen ant, workers, and eggs and larvae. Or, it may be termites which discover the tree as a food source, particularly the subterranean termites which live underground, but which feed on all manner of wood and wood products above ground, taking the food back down to their hungry colony below. Woodpeckers dig holes in the bark looking for bugs to eat or storing acorns, branches fall off to expose cavities that birds or squirrels enlarge for their homes, and thus it goes, perhaps for 40 or 50 years, until the tree is weakened enough that it blows down in a strong windstorm.

Now that it is laying on the ground another procession of bugs, mammals, worms, and fungi work away at it, and eventually – maybe 80 to 100 years after it had died – all that is left of that magnificent tree is a long pile of sawdust, nourishment needed by the forest for another generation of trees to grow from. This recycling process is the vital need of the forest to take all the energy and nutrition locked up in the tree, and convert it to material that can be re-used by the forest and its citizens. Beetles are an important link in that process of keeping the forest floor from being littered with piles of dead trees. In a hot, humid rainforest environment this process proceeds much more quickly than it does in the cool temperate forests of North America, but the same general procession of animals works away at the tree to reduce it to usable material.

Hopefully this will of help to you, for the next time you discover some bugs in your house, particularly in the winter when bugs are not supposed to be active. Quite often there will be no real reason to kill the insect or to treat your home, but instead we should just offer the poor, lost critter the opportunity to find the open door so it can get back outside where it can continue with its necessary and helpful role in nature.