Bagworms are caterpillars that live in distinctive spindle-shaped silk bags covered with small bits of leaves from the host plant. Large populations of bagworms can strip plants of their foliage and eventually cause them to die. Infestations often go unnoticed because people mistake the protective bags for pine cones or other plant structures. For more information, see Entfact 440.

A pest that can also attack agricultural crops, Potato leafhoppers can be pests of maples in nursery production. Other trees susceptible to damage are apple, ash, birch, crabapple, dogwood, oak, elm, hickory, and redbud. The adult is 1/8 inch long, pale green, and wedge-shaped. Nymphs are smaller but look similar to adults otherwise. This pest migrates north in the spring but cannot overwinter in colder states. Individuals feed with piercing-sucking mouthparts that create diagnostic damage called "hopperburn". They inject a toxin with their saliva that deforms leaf tips, curling them and turning them brown.

Woolly alder aphids require both alder and silver maple. Infestations of this insect are easy to recognize because they form white fuzzy colonies on foliage, twigs, or bark. These insects produce large amounts of sweet, sticky liquid waste (honeydew) as they feed. Deposits of this material attract bees, wasps, and flies, and support growth of sooty mold fungus on surfaces where it accumulates. Heavily infested leaves may drop prematurely.

Gloomy scale is an armored scale commonly found on red and silver maples. It can be found on many other plants, including sugar maple, boxelder, sweet gum, hackberry, and more. Research at North Carolina State University has shown they are more common in urbanized areas. The waxy covering of gloomy scale blends in with tree bark but does have a pale ring to distinguish it. Symptoms of heavy armored scale infestations are branch dieback and a thin canopy. The immature form of these scales is called a crawler and is the most susceptible stage to control. Gloomy scale crawlers begin emerging in May.

Cottony maple scale is a soft scale that infest maples, boxelder, basswood, birch, elm, and linden trees. This species overwinters as a small immature form and moves to find feeding spots in the spring. By June individuals become mature and egg sacs become noticeable. The eggs hatch in June or July and immature crawlers move to leaves to feed. As autumn approaches, they will move toward bark for winter protection. The adult female scale is 1/8 inch long, brown, and oval. Symptoms of an infestation include dieback, large amounts of honeydew, and black sooty mold.

Oystershell scales are about 1/10 inch long and resemble crusty accumulations of oyster shells on the bark. Their drab, bark-like appearance makes them easy to overlook, even on close inspection. Heavy infestations can kill twigs or branches. This scale overwinters in the egg stage under the waxy covering of the female. The eggs hatch and the crawlers are active from late May to early June.

Twig pruners are the larvae of small beetles that tunnel in twigs and small branches. Female beetles lay their eggs about the time of bud break in the spring. Eggs are laid in small holes which are chewed into the bark. The larvae that hatch from these eggs bore into and tunnel toward the base of twigs. In late summer, they chew concentric circles outward toward the bark then move toward the tip. The twig eventually snaps and falls to the ground. The larva pupates in the fallen twig and emerges as an adult in the spring. Collecting and destroying fallen twigs can help to reduce infestations.

Maple petiole borers are small caterpillar-like insects that tunnel into leaf petioles, weakening them and causing premature leaf drop. They are the larval stages of a sawfly wasp. Leaf loss is seldom enough to affect tree health. For more information, see Entfact 405.

Maple shoot borer (also known as maple tip moth and maple twig borer) This moth usually attacks red or Freeman maples but can also be found in sugar maples. It can be a serious pest in nursery production, where its tunneling can cause dieback and permanent disfigurement of the plant. The adult moths are active March-May and the female lays eggs on twigs near green-tipped or opening buds. After hatching, the caterpillar will burrow into the shoot and feed until May or June. During this time, you might notice a small hole where frass accumulates. The caterpillar will leave the tunnel and pupate around June. For more information, see Entfact 455.

Felt or erineum galls are produced by several species of mites. These appear as light green to yellow-green or crimson velvet-like patches on the underside of leaves.

Maple bladder galls occur on silver and red maples. These hollow rounded growths are attached to upper leaf surfaces by narrow stems. Initially, they are green but change color and darken as they mature. Heavily infested leaves may "cup" and drop prematurely. The single mite inside each gall feeds and lays eggs. Activity usually ends in July and the mites pass the winter under bud scales, moving back to leaves as they open in the spring. Outbreaks may occur occasionally but natural enemies generally keep infestations in check.

Maple spindle galls are long, narrow growths on the upper surface of sugar maple leaves. The life cycle is similar to that of the maple bladder gall.

The most striking gall on red maple, and occasionally sugar and silver maple, the maple eyespot gall (also called the eyespot midge gall), is caused by a small fly (midge). The small fly lays its eggs in the undersurface of leaves. The maggot that hatches from the egg develops quickly, producing a growth regulating-hormone which causes the development of bright red and yellow rings around the gall, usually in June. The 1/4 inch diameter area later turns brown. The maggot inside the gall completes its development in about 10 days. It then drops to the ground to pupate and transforms into the adult. There is one generation each year.

The gouty vein gall midge is a small fly that causes thickened swellings or purse-like growths on the upper leaf surface along major veins.