The smallest creatures that live in trees are also the most abundant: insects. These animals perform a wide range of ecosystem services that help every tree specimen thrive within the wider canopy. In this article on Nashville wildlife, we’ll take a look at the important role of insects and other invertebrates in plant reproduction and the transfer of nutrients across the food web, as well as how these tiny contributions have big results across entire ecosystems. Toward the end, we discuss how residents can apply this knowledge to support the trees and wildlife on your property and in your community.

The Tree Canopy as an Insect Habitat

Tree preservation is a cornerstone of broader environmental conservation efforts, and managing our trees for wildlife habitat is an effective way for individuals and organizations (such as NTCC) to take impactful action in supporting the interconnected web of life. By taking good care of trees, we’re also caring for the wildlife these specimens host season to season, year over year.

Insects and other invertebrates can be found living under, in, and throughout all parts of any given tree that you see:

• Roots: Many insects live in the soil under trees, while certain species, such as root weevils and some ants, burrow into and feed on the woody material. Cicadas spend their adolescent stage under trees, emerging annually or in multi-year intervals.

• Trunks: Many insects live under the bark of trees, like moths, ants, and beetles, while other beetles and termites burrow into tree trunks. Some insects, including bees and wasps, nest in small holes or cavities.

• Branches and Twigs: Spiders, in particular, can be found living among the branches and twigs of tree limbs, where they build webs to catch other small invertebrates like mites, aphids, caterpillars, and flies.

• Leaves: Caterpillars, leafhoppers, and aphids can be found on the leaves of trees, where they chew the leaves or suck out the sap of the fresh greenery.

• Flowers and Fruit: Insects like flies, bees, butterflies, and beetles visit the flowers and fruits of trees for their sugary, nutritious content. Many small invertebrates (such as worms, flies, and beetles) live in or lay their eggs in decaying fruit.

• Pollen and Nectar: These flower products are important sources of nutrients for bees, butterflies, flies, moths, beetles, and many other insects that also participate in the reproductive cycle of trees. 

• Decaying Parts and Deadwood: Carpenter ants and termites can be found in decaying portions of trees or in the deadwood of standing or fallen specimens. Certain beetles feed on fungi that grow on decomposing wood.

Some insects and small invertebrates, like spiders, wasps, and ladybugs, prey on smaller sap-sucking insects. Ants and wasps also feed on honeydew, the sugary secretion of sap-sucking insects like aphids.

The health and species of a tree are factors in which populations it can host. Some insect species are generalists and can live in various kinds of trees and plants, while other insects have exclusive relationships with specific kinds of trees (more on that later!).

How Do Trees Benefit From Insects?

By providing habitat for insects and small invertebrates, trees benefit in several ways from the presence of our smallest friends:

• Pollination: While some trees pollinate via the wind, many trees rely on the visitation of bees, butterflies, moths, and other insects to collect and deposit pollen as they visit flowers throughout their day. This helps trees reproduce by growing seeds, while some cross-pollination helps keep a species fit over generations.

• Nutrient Decomposition: Insects play vital roles in decomposition and making nutrients available, both by eating and being eaten. By eating live plant material, insects help process and release nutrients that either become available to trees through the soil or are further decomposed by predators who consume insects. Termites and carpenter ants contribute to breaking down living and dead wood, while some beetles carry fungal spores that help decompose dead tree material.

• Insect Population Control: Insect population numbers are maintained in nature so their numbers don’t overwhelm trees, other wildlife, or human residents. Not only do many insects eat other insects, but the presence of insects attracts predators like birds, mammals, reptiles, and amphibians which further contribute to keeping a tree’s host population at a healthy level.

• Soil Aeration: The huge population of insects that live below the trees and among the roots helps digest organic material that releases nutrients and moves the soil particles around, which allows space for oxygen and water to be present in the ground for roots to absorb as necessary.

• Tree Resilience: The presence of good insects on a tree creates small disturbances that help develop a tree’s defenses and grow tougher (just like wind helps a tree grow firmly with an ability to sway). 

Co-Evolution of Native Trees and Insects

While the generational turnover of insects and other small invertebrates is quick, the evolutionary relationship between insects and tree species in North America is ancient. In addition to the services provided to trees, such as pollination and nutrient decomposition, certain species of insects are dependent on particular species of trees (or other plants) for habitat and sustenance. When this is the case, some trees end up developing a defense against those insects, ensuring their continued existence.

For example, certain species of aphids have co-evolved with maple trees to feed on their sap, as well as with ants who feed on the honeydew of aphids in exchange for protection from predators. Another symbiotic relationship is between oak trees and gall wasps, who lay their eggs in the branches of oaks, which then develop a bulbous growth that the wasps have evolved to mature within and feed upon, benefitting from the protection of the woody expansion.

Pine bark beetles have co-evolved with coniferous trees like firs, spruces, and pines, in whose trunks the insects bore and lay their eggs. The beetles have developed a resistance to the tree’s defensive resin production, which would overwhelm other insect borers, while the trees have evolved resistance to the beetles. Similarly, the invasive emerald ash borer has decimated North American ash populations, but new cultivars of ash trees are being grown that are bred for robustness against the presence of these beetles.

When Is an Insect a Pest?

The relationships between small invertebrates and trees are dynamic and complex. Since so many insects are vital for the growth, maintenance, and overall health and condition of a tree, it can be challenging to grapple with the presence of insects that are weakening and damaging a local tree or species population. This can happen in various ways:

• Spread of disease

• Damage from boring

• Invasive insects

Any insect that moves from tree to tree is able to carry disease with it, the primary carriers being certain beetles, moths, leafhoppers, aphids, and scale. Other insects, like beetles, termites, and carpenter ants, create damage to trees by boring holes and tunnels through the living tree’s wood, which can impactfully disrupt nutrient and moisture circulation.

Invasive species, against whom native trees don’t have defenses, cause direct damage to trees as vectors of disease or through extensive boring habits (like the emerald ash borer). When local tree populations are damaged, it removes habitat for important native insect populations, which has effects across entire ecosystems. There are several steps we can take to protect against the spread of invasive insect species:

• Plant native plants

• Inspect newly acquired plants for infestation

• Keep yards clean of excessive debris

• Use local firewood

If you notice an invasive insect or suspicious damage to a tree, report it by contacting your local university extension office or a certified arborist to check it out. Experts will be able to confirm the presence of the insect, possibly treat your tree, and record the data to help manage an area-wide situation.

What Is the Tennessee State Insect?

The Tennessee state government’s website lists three small invertebrates as state symbols: the firefly, ladybug, and honeybee. 

Fireflies, or lightning bugs, are the friendly evening beetles that hover and glow with their bioluminescent bodies in yards, fields, and forests. They live at the soil surface but use trees to perch and mate, flashing their lights to attract females. Females that remain in a larval form through adulthood are known as glowworms.

Ladybugs, or lady beetles, are the round, black-spotted red insects we know and love. They can be found in beautiful contrast against the green leaves of bushes and trees, where they are actually important insect predators; ladybugs help manage aphid populations in particular. 

Honeybees are important for honey production and as a generalist pollinator, but they don’t substitute specialized pollination relationships that wild bees have with native plants! However, all types of bees are complementary and support the health of the wider ecosystem.

We can help protect and maintain beneficial species populations like fireflies, ladybugs, bees and many others by keeping our yards in hospitable condition. Planting native trees and using leaf litter in the yard to provide protective cover are just two ways to help: this is where many insects and other small invertebrates find shelter over the winter. Leaf litter that protects insects also creates food sources for birds and other wildlife through the colder months of the year and into spring.

Landscaping to Support Insect Populations

Insect populations are generally declining due to habitat loss, which is arising from deforestation, indiscriminate development and urban expansion, pollution, temperature increases, and other environmental changes and land use decisions. The impact of a lower insect population is a loss of ecosystem services performed by insects, such as nutrient cycling, food provision for larger wildlife, pollination of most plants, and the resulting loss of ecosystem services performed by all other plants and animals that can’t be supported without the presence of those insects. 

Luckily, there are choices residents can make about their own properties that can help support local insect populations. This includes:

• Planting multiple types of native trees, shrubs, flowers, and grasses that attract general and specialized insects.

• Setting aside wild patches in your yard or garden where insects can find and build shelter to hide from predators (a bee hotel is a great way to support wild bee populations).

• Minimizing pesticides and chemical use in the yard and finding natural solutions when possible.

• Providing water sources, like bird baths or dishes that can collect rainwater, where insects can find a drink.

• Using organic mulch and compost, which attract wildlife as habitat cover and a food source; in turn, they contribute to breaking down the material and releasing nutrients into the soil.

Support the Environment by Protecting Good Bugs

You can help create a habitat conducive to attracting and hosting the insect populations in your neighborhood by browsing the Nashville Tree Conservation Corps’ tree sale for a new contribution to your yard! If you’re unable to plant a tree, you can donate a tree for us to plant or lend us a hand at one of our volunteer events. Financial donations of any amount are an impactful way that Nashville residents can help support our mission to plant and maintain trees across the city, and you can stay connected with us by subscribing to our newsletter. Check out our Linktree to connect with us in other ways, too!