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Column: Moment of Nature - Aug. 24, 2018

Critters in trees

Posted: August 23, 2018 4:34 p.m.
Updated: August 24, 2018 1:00 a.m.

Trees provide necessary places for all types of animals and insects to use as a lounge, a home, a nursery and daycare center as well as a restaurant. One such insect that uses trees for one-stop shopping is the fall webworm (Hyphantria cunea), a common native caterpillar. These little caterpillars hatch from eggs that were laid on the underside of leaves in early summer. As they grow they form a protective webbed barrier around themselves and their leafy food source. As its name implies, the ‘web’worm forms a cobweb on the ends of twigs, clumping them together for protection.

Webworms are categorized as defoliators, meaning they eat leaves for food. Once large enough to do so they go right to work nibbling the leaves of their host tree. Their favorite trees are our native persimmon, pecan and sourwood, but are also found in ornamental cherry and other commonly planted urban trees.

Once the caterpillars reach maturity, they form a cocoon and overwinter as pupae among leaves and organic matter on the ground or in the upper layer of soil. The adult moth emerges in the spring, finds a host tree, lays eggs and the cycle of life begins again.

If you have a tree in your yard occupied by webworms know that 1) they are there temporarily, up to 3 – 5 weeks, 2) they are there because they exist in nature and their presence is not an indication that a tree is unhealthy or diseased, 3) they are not a threat to the life of a tree, 4) the defoliation of some clumps of leaves will not significantly affect tree health and 5) the use of pesticides to eradicate them is not necessary.

While the webworm is not a threat to the life or health of a suburban tree, the cobweb or tent as it is commonly referred to, is unsightly and can (temporarily) detract from the aesthetics of a landscape. If you prefer not to have your tree leaves eaten and don’t want to look at the tents, the most eco-friendly way to get rid of the caterpillars is to either prune off the branches if they are low enough to reach or to break open the tent. This can be done by using a broom handle or other long implement or use a high-pressure nozzle attached to a garden hose. Physically opening up the tent exposes the caterpillars, which provides an accessible food source for song birds and other insect-eating animals. This option saves time and money from not having to buy and apply pesticides while providing a food source for birds, a win/win!

Another critter commonly seen on and in trees and one that I get a fair amount of calls on is the carpenter or black ant (Camponotus pennsylvanicus).  There are over 30 different kinds of ants (both foreign and native) to the southeast, but for sure one of the largest of them is the black carpenter ant.

Carpenter ants and their nests are very common inside trees, especially older trees that have a hollow cavity in the trunk or branches. The nests are usually built in already rotten or decaying wood. Common belief is carpenter ants can kill a tree by devouring the wood, this is absolutely not true. Carpenter ants are not harmful to a tree. Stress, mechanical injury, environmental conditions, disease or other insects are responsible for killing limbs or sections of a tree in which the ants are able to nest. Once injury to a tree has occurred, wood decay can set in and it is the decaying wood that gives the carpenter ants the opportunity to colonize the tree. These ants use knots, cracks, holes and old insect tunnels to gain access to these areas.

Ant control is not necessary for the tree’s health, as the ants are only taking advantage of a great living environment -- soft, moist wood in which to establish their colony. Besides, control of carpenter ants inside a tree is difficult at best and for the most part unnecessary. Available pesticides on the market to control them are not likely to permanently rid a tree of carpenter ants so retreatment every year or so may be necessary if the ants are bothersome. Keep in mind though, that most insecticides kill good bugs as well as bad bugs and may have residual life in the soil or be harmful to aquatic life if washed down the road and into creeks or ponds.

In addition, plugging or sealing tree cavities is not advised. Such treatments are unnecessary and will not eliminate nor prevent decay or carpenter ant activity. Also, cutting down an otherwise healthy viable tree just because it happens to have carpenter ants inside is not only wasted time and money it’s also a loss of a valuable landscape asset. Removing the tree would more likely disperse the ant colony and make them look for other housing locations, perhaps a house or shed.

While folks may think of ants as pests, only a few of our Southern species infest homes or cause problems for home landscapes. Overall, carpenter ants are really quite beneficial to the environment, playing a vital role in aerating soil, recycling nutrients and serving both as predators and prey in the great fabric of life.  As I often say, you can’t stop nature from happening and in the case of carpenter ants, better to keep them in the trees!


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