Nature Trivia
By: Renn Tumlison and Kristen Benjamin
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Plant Galls
| Galls are abnormal, vegetative growths that are usually formed as a response by plants to the action of fungus, mites, or insects such as wasps, aphids, and true bugs. Galls can be formed in the leaves, petioles (stem) of leaves, twigs, buds, or on the roots. |
Oak Galls
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Several species of gall wasps are responsible for the formation of the leaf galls known as "oak apple galls." Oak apple galls have a firm to hard outer shell when dried (center photo) and are filled with a fibrous or spongy material, and may be attached to the tree by the leaf petiole or may be formed on a seemingly normal leaf. These galls appear in the spring (left photo) and may remain on the tree into the fall. The causative agent of the oak apple gall shown above is a parasitic wasp, Biorhiza pallida. The fibrous strands filling the inside of this gall are visible above in the photo on the right.
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The thin-shelled gall pictured above left was caused by the gall wasp Loxaulus maculipennis. In the image on the right, the gall has been cross-sectioned to reveal the contents - a small amount of fibrous material radiating outward from a central point inside the shell.
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| Wool-sower galls (left photo) are 1 1/2 inch to 2 inch long woolly twig galls with reddish seed-like grains. Woolly oak leaf galls (pictured right) are similar in appearance to a dense wad of light brown wool attached to the midvein of the leaf (although occasionally are found on the lateral veins). Both wool-sower and woolly oak leaf galls are caused by parasitic gall wasps belonging to the genus Callirhytis. |
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| The white, woolly twig gall in the photo on the left is caused by Andricus furnessae, a species of gall wasp. Another species of gall wasp, Plagiotrochus punctatus, is the causative agent for the gouty oak gall (pictured right), which occurs on twigs. |
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Eastern oak bullet galls (pictured above) are smooth, spherical galls approximately 1/2 inch in diameter produced by a wasp of the genus Disholcaspis. These galls are very hard because they form from the tough, woody tissues of twigs.
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| The large swellings, such as the one on this oak, are caused by either bacterial or viral infections. The growth is similar to a tumor and can be as large as a meter (over three feet) wide. |
Hickory Galls
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| The small galls on the underside of the hickory leaflet pictured on the left are caused by Phylloxera caryaefallax, a species of plant louse. The globular hickory leaf galls in the center photo are produced by the plant lice Phylloxera caryaeglobuli. The causative agent of the hairy, globular leaf galls (shown in photograph on the right) are gall midges belonging to the genus Caryomyia. |
Elm Galls
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The globular leaf galls (above left) and the elm finger galls (above right) were caused by a species of mite belonging to the genus Eriophyes.
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Hop-hornbeam Gall
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| The globose, red-tinted pocket galls on the hop-hornbeam leaf pictured above were caused by tiny (1/25 - 1/12 inch) mites belonging to the genus Eriophyes. |
Pine Galls
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| Round galls formed on the main stem or branches of pine trees (the primary host) are evidence of the presence of the eastern gall rust disease, which is caused by the fungus Cronartium quercuum f. sp. quercuum. Oak trees (Quercus sp.) are utilized by this fungus as alternate hosts (as is reflected in the species name of the fungus). The gall and its host pine branches pictured in the photograph on the left are alive. The image on the right is of a branch that has been killed by this disease. |
Cypress Galls
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The cypress twig gall midge, Taxodiomya cupressiananassa, causes swellings on bald cypress branches with some leaves included in the galls. The first two images courtesy of Larry Hime.
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Cedar Gall
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| A fungus called Gymnosporangium juniperi-virginianae causes this unsightly cedar apple rust gall to appear on eastern redcedar trees (alternate host). The fungus overwinters inside these galls, then the orange jellylike "horns" (called telia) seen in the above photograph grow out of the gall in the spring and produce spores which may infect apple leaves to continue the life history of the fungus. |
Hackberry Gall
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Hackberry petiole galls (see swelling at top of lower leaf) are caused by jumping plant lice of the genus Pachypsylla, which resemble tiny cicadas. Nymphs overwinter in the galls, and the dead leaves tend to remain on the trees until autumn.
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Dogwood Gall
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| The dogwood club gall is not as obvious as most galls, appearing as a brownish swelling at the end of what normally would be a green stem (above image). This gall is caused by Mycodiplosis alternata, a species of gall midge (a fly). |
Blueberry Galls
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The gall wasp Hemadas nubilipennis causes kidney-shaped galls with a diameter of approximately 1/2 to 1 inch to form on blueberry stems (pictured above).
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Blackberry Gall
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Round or elongated (2 to 6 inches in length) blackberry stem galls with deep, longitudinal furrows are caused by the gall wasp, Diastrophus nebulosus. These stem galls are known as blackberry knot galls (pictured above).
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Poison Ivy Galls
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| These puckered, irregular, wart-like galls on poison ivy are caused by an Eriophyid mite, Aculops toxicophagus. |
Goldenrod Galls
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The Goldenrod Gall Fly (Eurosta solidaginis) lays its eggs in the stem of the goldenrod. The plant reacts to the larva's chewing at the affected site by swelling into a ball (left photo). This phenomenon creates a "goldenrod gall." Notice the small hole near the base of the gall. This is the hole from which the fly exits after maturing. The spindle-shaped gall in the photo on the right is made by the larval stage of a moth (Gnoremoschema gallaesolidaginis).
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Black Gum
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The leaves of black gum (Nyssa sylvatica, seen here) sometimes show folding or curling of leaf margins due to either midges (Cecidomyia nyssaecola) or mites (Eriophyes sp.).
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Renn Tumlison
Department of Biology
Box 7861
Henderson State University
Arkadelphia, AR 71999
Phone: (870) 230-5152
E-mail: tumlison@hsu.edu
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