If you’ve spotted webbing on your trees or shrubs in Maryland, it’s likely the work of pests. Some are harmless, like barklice, while others, such as spider mites, eastern tent caterpillars, and fall webworms, can cause significant damage. Here’s what you need to know:

• Spider Mites: Tiny arachnids that create fine webbing on leaves. They damage plants by feeding on sap, leaving yellowed or stippled leaves.
• Eastern Tent Caterpillars: Spring pests that build thick silk tents in branch forks, defoliating trees like cherry and apple.
• Fall Webworms: Late-season caterpillars that spin webs at branch tips. They target over 100 tree species but mostly cause cosmetic damage.
• Barklice: Harmless insects that create silk-like sheets on tree bark. They clean algae, fungi, and debris from the tree surface.

Quick Tip: Identify pests by webbing location, season, and visible damage. Early detection and regular monitoring are key to protecting your plants.

Regular inspections, proper plant care, and timely intervention can prevent severe damage. If unsure, consult a professional for pest management.

Spider Mites – How to Identify and How to get Rid of Them

Spider Mites: Small Pests That Cause Major Problems

Spider mites might be tiny, but they can wreak havoc on Maryland landscapes. These nearly invisible arachnids – more closely related to spiders and ticks than insects – can quickly turn vibrant, healthy plants into damaged, discolored ones covered in fine webbing ^[6].

What makes them even more troublesome? Female spider mites can reproduce without mating, and when temperatures range from 70°F to 85°F, they can produce multiple generations in just one season. This rapid reproduction can turn a minor issue into a major infestation in no time ^[6].

How to Identify Spider Mites

Spider mites are incredibly small, measuring less than 1/16 inch (1–2 mm) and sometimes as tiny as 1/60 inch. Their oval bodies come in a range of colors, including pale yellow, brown, purplish, orange, or red. Some species even shift colors throughout the year ^[6][7].

“Mites are arachnids, the group to which spiders and ticks belong; they are not insects.”
– Miri Talabac, Horticulture Coordinator, HGIC ^[6]

To detect these pests, try the white paper test: gently tap leaves over a white sheet of paper and watch for tiny moving specks. For a closer inspection, use a magnifying tool – 10× magnification is often enough, though some species might need up to 30× to be seen clearly ^[6].

One of the most obvious signs of spider mites is fine silken webbing draped over leaves, buds, flowers, and stems. You might also notice white, grainy debris in the webbing, which are the mites’ shed skins (exuviae). Spotting these indicators can help you identify plants that might be at risk of a growing infestation ^[6].

Plants Spider Mites Attack Most

Spider mites are notorious pests of ornamental plants in the southeastern United States, and Maryland is no exception. The twospotted spider mite alone can attack over 1,000 plant species, making nearly every landscape plant a potential target ^[9]. In Maryland, common hosts include maples, azaleas, and roses, but other vulnerable plants include arborvitae, boxwood, camellia, elm, fir, fruit trees, hemlock, hollies, juniper, oak, rhododendron, and spruce ^[10].

Seasonal activity varies by species. In Southern Maryland, twospotted spider mites are most active in the warm months of spring and summer, while spruce spider mites thrive during the cooler periods of spring and fall ^[8]. Even within plant species, susceptibility can differ. For instance, European/common boxwood is highly prone to damage from boxwood spider mites, while littleleaf/Japanese boxwood tends to resist them better ^[6].

Warning Signs of Spider Mite Problems

Catching spider mites early is crucial. When their numbers are low, damage may not be obvious. But as their population grows, the signs become hard to miss. Look for stippled, yellowed, or bleached leaves, along with stunted plant growth ^[6]. Check the undersides of leaves, especially along the main veins, where fine webbing often appears. Feeding damage typically shows up as tiny yellow or brown spots, which can sometimes be mistaken for damage from other pests like leafhoppers or lace bugs ^[6].

Other warning signs include brittle, curled, or twisted leaves with discoloration and speckles. Severe infestations can lead to premature leaf drop and thick webbing that may cover entire branches. Regular monitoring – especially during hot, dry weather – is your best defense. Inspect plants every week or two to catch problems before they spiral out of control ^[8][10].

Eastern Tent Caterpillars: Spring Web Makers

Eastern tent caterpillars (Malacosoma americanum) are one of Maryland’s most noticeable springtime insects, known for weaving large silk tents that drape across trees. These native pests emerge in early spring, creating communal shelters that can house hundreds of caterpillars at once ^[4].

Unlike spider mites, which spin fine webbing on leaves, eastern tent caterpillars construct thick, silk structures that act as their shared homes. Fully grown caterpillars can reach about 2 inches long and are easily identified by their bold patterns, including a distinctive white stripe running along their backs. This stripe sets them apart from similar species, such as gypsy moth caterpillars, which are marked with red spots instead ^[4][11].

When and Where to Spot Eastern Tent Caterpillars

In central Maryland, eastern tent caterpillar eggs usually hatch around the first week of April, though this can shift depending on the weather. During the cool, damp days of early spring, these caterpillars stay tucked inside their silk tents. They prefer trees in the Rosaceae family, such as apple, cherry, and crabapple, so these are good places to look from April through May ^[4].

Most of the feeding damage happens in May, once the caterpillars have grown large enough to consume significant amounts of foliage. By late May, they begin pupating. Outbreaks of eastern tent caterpillars tend to follow a cycle, occurring roughly every 8 to 10 years. After a long stretch of low activity, a sudden infestation can catch tree owners off guard ^[4][12].

Where They Build Tents and the Damage They Cause

Eastern tent caterpillars typically build their silk tents in branch crotches, unlike fall webworms, which create their webs at branch tips ^[4]. Early in the season, the tents are small, but as the caterpillars grow, the structures become much larger and more noticeable, especially on smaller ornamental trees.

Large populations can strip entire branches or even whole trees of their leaves. Each egg mass contains between 150 and 350 eggs, meaning hundreds of caterpillars can emerge from a single overwintering site ^[12][13]. While healthy deciduous trees can usually recover from complete defoliation for several years, young or stressed trees may suffer severe damage ^[12][4][14].

Fortunately, nature provides some balance. Birds like yellow-billed and black-billed cuckoos are natural predators of eastern tent caterpillars and can eat up to 200 of them in one meal, making them valuable allies in managing these pests ^[4].

Fall Webworms: End-of-Season Web Builders

Fall webworms (Hyphantria cunea) are caterpillars that show up as summer gives way to fall, spinning silk webs that are hard to miss. Unlike eastern tent caterpillars, which spin their webs at branch unions in spring, fall webworms build their silk shelters at the tips of branches later in the year ^[15].

These caterpillars emerge between July and October, targeting trees that are nearing dormancy. This timing means their feeding doesn’t usually cause significant harm – most of the damage is purely cosmetic ^[5][2].

Fall Webworm Life Cycle and Appearance

Fall webworms follow a predictable seasonal cycle, but their appearance can vary, making identification tricky. Late-stage caterpillars, for instance, come in different colors depending on their region ^[15].

Fully grown larvae are about an inch long and come in two main forms. The northern variety is yellowish-white with black heads, while the southern type is brown with red heads. Both have paired black tubercles and are covered in silky gray hairs ^[2][18].

The adult moths are small, about 3/4 inch long, with white wings that may have black spots ^[2]. Female moths are prolific, laying between 400 and 1,500 eggs on the undersides of leaves ^[16][18]. After hatching, the caterpillars overwinter as pupae in cocoons, which they tuck just beneath the soil surface or hide in leaf litter ^[18].

Trees Fall Webworms Prefer and When They Attack

Fall webworms are not picky eaters. In North America alone, they feed on more than 100 species of deciduous trees, and globally, they’ve been found on 636 different plant species ^[2][15]. In Maryland, their favorite targets include mulberry, walnut, hickory, elm, sweetgum, poplar, willow, oak, linden, ash, and apple trees ^[2].

Interestingly, they tend to build their webs on the south-facing sides of trees. Inside these webs, temperatures can soar to 104–122°F, which creates ideal conditions for the larvae to grow ^[2][17].

In Maryland, the first generation of fall webworms typically appears in July. A second generation follows, staying active from August through October ^[5][2]. Their webs, which start small, expand quickly as the caterpillars grow and consume more foliage.

How Fall Webworms Affect Tree Health

Since fall webworms attack trees late in the growing season, their impact is mostly cosmetic. By the time they start feeding, the leaves have already done the heavy lifting of producing food for the tree. This means that while their webs and defoliation might look alarming, healthy trees usually recover without any lasting harm ^[18][19].

That said, trees already under stress might suffer additional weakening. If you want to manage the webs for aesthetic reasons, you can prune or wash away smaller ones and dispose of them in soapy water. For larger infestations, applying Bacillus thuringiensis early on can help, followed by washing away any remaining webs ^[18][19][20].

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Barklice: Harmless Web Producers on Tree Bark

Barklice might look like troublemakers, but they’re actually nature’s clean-up crew for your trees. These small, soft-bodied insects spin silk-like webs on tree trunks and branches – not to harm them, but to keep them clean. Their work makes them a unique addition to the ecosystem.

Also known as Psocoptera, which translates to “winged insects that gnaw,” barklice are often mistaken for harmful pests because of their webbing ^[21]. But here’s the good news: they’re not related to parasitic lice, and they’re completely harmless to trees and humans. With over 300 species across North America, they’re more common than you might think ^[22].

What Barklice Do and How They Behave

Barklice use their silk webbing for two main purposes: to protect themselves from predators and to maintain moisture. Blake Layton, an Extension Entomology Specialist at Mississippi State University Extension Service, explains:

"The sheets of webbing they produce provide protection from predators and help maintain a more humid and favorable environment for the entire community." ^[23]

These insects are scavengers with an important job – cleaning trees. Their diet consists of mold, algae, lichen, dead bark, and even dead insects ^{[21][22][24][25]}. As Susan Patterson from Gardening Know How puts it:

"The lice do not actually hurt trees and are often thought of as helpful because they clean trees by eating things that your tree does not need like fungi, algae, mold, dead plant tissue, and other debris." ^[25]

The webbing they create can sometimes cover entire trees, from the trunk’s base to the branches’ tips, especially in late summer when their activity peaks ^[22][24][26].

What Barklice Look Like and Which Trees They Choose

Barklice are tiny, measuring just 1/8 to 1/4 inch long, with brown coloring that helps them blend seamlessly into tree bark ^[22][27]. Adults have wings that they fold tent-like over their backs and long antennae that are easy to spot ^[22][24].

Certain trees seem to be their favorites. In Maryland, for instance, barklice are often found on oaks, elms, and maples, as well as hollies ^[23]. In 2018, a species known as Cerastipsocus venosus, known for its colorful appearance, was frequently spotted on holly trees throughout the state ^[28].

Their webbing is most noticeable during humid weather, which creates ideal conditions for their activity ^[27]. If you come across barklice webbing, the best thing to do is leave it alone. They’re doing your trees a favor by cleaning them. Clemson University Extension emphasizes this point:

"Barklice are harmless; their presence only indicates that a suitable habitat exists in the area or on that tree." ^[22]

If the webbing bothers you, a strong spray of water can remove it, but it will naturally disappear over time. The Galveston County Master Gardeners describe their role perfectly:

"As scavengers, they perform a valuable function in consuming excess accumulations of fungi, algae, dead bark and other materials that occur on tree trunks and large limbs – in effect, they function as Bark Maids to help clean the bark of undesirable inhabitants." ^[27]

Quick Reference: Maryland Webbing Pest Identification

Noticing webbing on your trees or shrubs? Identifying the culprit quickly can help you decide whether action is necessary or if observation is enough. Different pests create distinct webbing patterns, making recognition easier once you know what to look for.

Pest Identification Table

This table highlights key characteristics, but timing, size, and webbing location can provide additional clues for accurate identification.

Timing is a major factor. For instance, Eastern tent caterpillars create their webs in spring, while fall webworms are active in late summer or early autumn. Spider mites, on the other hand, spin their delicate webs throughout the growing season.

Size and visibility also vary. Spider mites are nearly microscopic, measuring just 1/60 of an inch, while caterpillars like Eastern tent caterpillars and fall webworms are much easier to spot. Webbing location further distinguishes these pests: fall webworms build webs at branch tips, Eastern tent caterpillars construct silken tents in branch unions, spider mites spin webs directly on leaves, and barklice weave silk-like sheets on tree trunks.

Each pest has its own impact. Spider mites cause severe leaf stippling, Eastern tent caterpillars can defoliate young trees entirely, fall webworms primarily affect a tree’s appearance, and barklice are actually beneficial, as they clean bark surfaces by removing fungi, algae, and dead material.

For management, act quickly against spider mites and Eastern tent caterpillars. Fall webworms generally only need monitoring, while barklice can be left alone or removed with a gentle water spray if necessary.

Protecting Your Maryland Trees and Shrubs

Keeping your Maryland trees and shrubs healthy means staying ahead of potential pest problems. Early detection is key – take mite infestations, for example. These are much easier to manage when caught early.

Make it a habit to inspect your landscape regularly. Look for signs like pale or yellowing leaves and fine webbing on branches, which can signal a pest issue ^[34][35]. Pay extra attention to plants that are especially vulnerable, such as roses, azaleas, and fruit trees, especially during peak pest seasons. Prevention is always better than dealing with a full-blown infestation. For instance, avoid over-fertilizing with nitrogen, as it encourages tender new growth that pests love ^[6]. Consistent watering, good air circulation, and avoiding areas with too much reflected heat can also make a big difference ^[6]. Don’t forget to remove weeds around your trees and shrubs – these can act as hiding spots for mites, which may eventually spread to your prized plants ^[6].

The types of plants you choose for your landscape can also make a big impact. Opt for pest-resistant varieties whenever possible. For example, littleleaf boxwood is far less appealing to boxwood spider mites than European boxwood ^[6]. Adding variety to your landscape can help attract beneficial insects, which naturally keep pest populations in check. Plus, providing a steady source of nectar ensures these helpful insects stick around throughout the growing season ^[6].

Sometimes, simple mechanical controls can help manage pests. For instance, you can hand-pick bagworm cases before they hatch. To keep spider mites in check, try rinsing dust off foliage regularly, as this helps their natural predators do their job ^[6]. If you need to prune heavily infested plants, be careful not to create overly dense foliage, which can restrict airflow and encourage more problems ^[6]. These small steps can set the stage for more effective pest control methods, whether mechanical or professional.

For severe infestations or hard-to-reach areas, it’s best to call in a professional. Arborists or experienced landscapers can handle large trees or pest issues high in the canopy ^[36].

If DIY solutions aren’t cutting it, Pro Landscapes MD offers expert garden and tree care services throughout central Maryland, including areas like Howard, Montgomery, Carroll, Frederick, Prince George’s, and Baltimore Counties. Their team of professional horticulturists specializes in early pest detection and targeted treatments to help protect your outdoor spaces.

Timing is everything when it comes to pest control. For example, Bt treatments for bagworms should be applied by mid-July to target young caterpillars effectively ^[3]. Resources like the National Phenology Network‘s Bagworm Forecast can help you predict when pests are likely to emerge ^[3]. Keep in mind, insecticides usually don’t work on mites and may even make mite problems worse. Use miticides only as a last resort, ensuring they’re specifically labeled for your plants and safe for the environment ^[6].

Healthy plants are naturally better at resisting pests. By focusing on proper care – like consistent watering and balanced nutrition – you can make your trees and shrubs stronger and more resilient against potential infestations. A little effort upfront can go a long way toward protecting your landscape.

FAQs

How can I tell if the webbing on my trees or shrubs is caused by spider mites or other pests?

To figure out if spider mites or other pests are responsible for the webbing on your trees or shrubs, take note of these key details:

• Web Texture and Placement: Spider mite webs are delicate and sticky, often wrapping tightly around leaves, stems, or branches. In contrast, garden spiders and similar pests create larger, more structured webs that rest on plants rather than encasing them.
• Pest Size and Appearance: Spider mites are tiny, measuring less than 1/20 inch, and often appear as tiny moving dots, usually on the undersides of leaves. Their colors can vary from pale green to red. Other web-spinning pests, like spiders, are much larger and can be spotted easily without magnification.
• Plant Damage: Spider mites feed on plant sap, often leaving behind yellowing or stippled leaves as evidence of their presence. Spiders, on the other hand, don’t harm plants directly – they use their webs to catch prey instead.

By closely inspecting the webbing, the pests, and any damage to your plants, you can pinpoint whether spider mites are causing the problem or if another pest is at work.

How can I effectively manage spider mite infestations in Maryland gardens?

To tackle spider mite infestations in Maryland, a few proactive steps can make a big difference. Start by spraying your plants with water. This simple action can dislodge spider mites from leaves and help reduce their numbers, especially in dry or dusty conditions. Plus, regular watering supports overall plant health, making them less vulnerable to pests.

You can also welcome natural predators into your garden. Ladybugs and predatory mites are excellent allies – they feed on spider mites and naturally keep their populations under control. Be mindful not to over-fertilize with nitrogen, as this can encourage mite growth. Instead, focus on proper plant care and reducing stress to keep your greenery thriving.

If the infestation becomes severe, consider using miticides specifically labeled for spider mites. Apply these products carefully, following the instructions to ensure safe and effective use while minimizing any impact on the environment.

What can I do to protect my trees from pests like eastern tent caterpillars and fall webworms?

To protect your trees from eastern tent caterpillars and fall webworms, here are a few effective steps you can take:

• Get Rid of Webs and Egg Masses: Regularly inspect your trees and remove small webs by hand. During winter, prune branches to eliminate egg masses before they hatch.
• Apply Safe Insecticides: Use biological insecticides like Bacillus thuringiensis (Bt) as soon as you notice webs or caterpillars. Acting early is key.
• Welcome Natural Predators: Create a yard environment that attracts birds and beneficial insects. These natural predators can help keep caterpillar populations in check.

Taking these measures can go a long way in keeping your trees healthy and free of pests year-round.

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• Biological Pest Control for Trees and Shrubs
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