An online resource based on the award-winning nature guide

Galls

Blueberry Stem Galls

3-29-17 blueberry stem gall IMG_7405Up to a dozen tiny black wasps (Hemadas nubilipennis) will emerge from this gall in the spring, around the time when blueberry bushes are flowering. After mating, the female wasp lays her eggs under the surface of the blueberry stems. Once she has completed her egg-laying, she climbs to the tip of the shoot and repeatedly stabs it, preventing further growth.

The plant reacts to the wasp’s egg-laying by forming a kidney-shaped gall. The majority of galls (up to 70%) are formed on stems within the leaf litter. These galls can be up to an inch in diameter, and they contain many developing larvae that feed on the walls of the gall and grow during the summer, overwinter as larvae, pupate inside the gall in the spring, and then emerge as adults when the blueberry bushes are in bloom in late May and early June. The adults are almost entirely females.

If a blueberry bush has many galls, it can be problematic.  A branch possessing a blueberry stem gall will not produce flower buds, and no flowers means no blueberries.

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Witch-hazel Cone Gall Aphids Laying Eggs

10-26-16-witch-hazel-gall-s20161017_5388At this time of year there is a species of aphid, Hormaphis hamamelidis, that is laying eggs on Witch-hazel branches. Next spring female aphids will hatch out of these eggs and begin feeding on newly-emerged Witch-hazel leaves. The aphids inject the leaf with a substance that causes the leaf to form a cone-shaped growth, or gall, around the insect, providing it with both food and shelter. The galls are hollow, and have openings extending out through the leaves’ lower surfaces. Within the galls the unmated female aphids produce 50 – 70 young. Eventually the galls fill with winged female aphids which emerge through the cone openings, disperse, and repeat the process. The third generation of aphids consists of both males and females which mate and lay their eggs on Witch-hazel. The aphids that hatch from these eggs create the conical galls found on Witch-hazel leaves.

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Female Sumac Gall Aphids Leaving Galls & Heading For Moss

9-22-16-red-pouch-gall-20160916_0115The sac-like galls found on Staghorn and Smooth Sumac are anywhere from marble- to ping pong ball-size, and usually become obvious in late summer when they often acquire a rosy pink blush. Inside the thin walls of these galls is one big hollow cavity, teeming with tiny orange woolly aphids (Melaphis rhois) referred to as Sumac Gall Aphids.

In the spring, female aphids lay an egg on the underside of a sumac leaf, causing the plant to form an abnormal growth, or gall, around the egg.   The egg hatches and the aphid reproduces asexually within the gall. Thus, all the aphids inside the gall are identical clones of one another. In late summer or early fall, the winged females fly to patches of moss, where they establish asexually reproducing colonies. At some point these clonal colonies produce males and females which mate and it’s these mated females that fly off to lay eggs on sumac leaves in the spring.

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Goldenrod Ball Galls Provide Important Source of Winter Food for Downy Woodpeckers

12-11-15 goldenrod ball galls 058A number of insects cause goldenrod plants to form galls – abnormal growths that house and feed larval insects. The Goldenrod Ball Gall is caused by a fly, Eurosta solidaginis. The fly lays an egg on the stem of a Canada Goldenrod (Solidago canadensis) plant in early spring, the egg hatches and the larva burrows its way into the stem; the plant reacts by forming a gall around the larva. The larva overwinters inside the gall, pupates in late winter and emerges in early spring as an adult fly. Prior to pupating, the larva chews an exit tunnel to, but not through, the outermost layer of gall tissue. (As an adult fly it will not have chewing mouthparts so it is necessary to do this work while in the larval stage.)

Downy Woodpeckers (and Black-capped Chickadees) have discovered this abundant source of winter food, and dine on the larva after chiseling a hole into the gall. Downy Woodpeckers tend to make a tidy,narrow, conical hole by pecking, while Black-capped Chickadees tend to make a messy, large, irregular hole by grabbing bits of the gall with their bill and tugging them free. While woodpeckers prefer larger galls that are located high on goldenrod plants growing near wooded areas, these are not the only factors taken into consideration.

A woodpecker extracts the fly larva through the tunnel the larva excavates prior to pupating, as this facilitates rapid removal of the larva. Downy Woodpeckers can determine whether or not a gall has an exit tunnel, and if it doesn’t, they usually abandon the gall without drilling into it. The likelihood of smaller parasitic wasp larvae occupying the gall (and a plump fly larva not being present) is much greater if there is no exit tunnel, and these smaller prey apparently are not always worth the woodpecker’s time or energy.

NB: Correction: this week’s Mystery Photo was of a Gray Birch (Betula populifolia) bract, not a Paper, or White, Birch (Betula papyrifera) bract. While similar, there are differences between these two species of birch that I should have recognized (especially when looking at the leaf!). Thanks to Kathy, an alert blog reader, who caught this error.

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Black Cherry – well known to most readers!

black cherry tree silhouette IMG_5114Black Cherry, more than most tree species, often has several identifying features even after it loses its leaves. The buds of Black Cherry have about ten scales, each of which is brown at the tip and green at the base. The bark of young Black Cherry trees is typically smooth, reddish in color and covered with grayish, horizontal lines called lenticels — small openings that allow the passage of gases in and out of the tree. The bark on older Black Cherry trees consists of squarish scales, curved outward at their vertical edges, somewhat resembling burnt potato chips. Black Cherry is one of several trees on which the fungus Apiosporina morbosa causes Black Knot Galls. Lastly, Black Cherry is the primary host for the Eastern Tent Caterpillar moth. These moths encircle Black Cherry branches with their egg masses, and the eggs hatch just as Black Cherry’s leaves emerge from their buds, providing food for the young larvae.

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Gall-making Mites on Sugar Maple Leaves

S6-2-15 mite-making galls 060Within a week or two of unfurling, Sugar Maple leaves are attacked and consumed by all kinds of creatures, some of which are insects and mites that cause the leaves to develop abnormal growths called galls. Certain species of eriophyid mites form felt, or erineum, galls, often on Silver and Sugar Maple leaves. After spending the winter months under the scales of buds, these mites emerge in the spring when leaves appear, move out onto the surface of the leaves and begin to feed. Their feeding induces the growth of thousands of tightly-packed leaf hairs which provide shelter for the mites on the leaf surface. These hairs appear as bright pink or red patches that resemble felt. The mites, too small to even be seen with a hand lens, move to the inside of these structures for the rest of the growing season.

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Woolly Oak Leaf Gall

11-28-14  woolly oak leaf gall IMG_3574Of the 2,000 kinds of galls found on North American plants, 800 different kinds form on oaks. One of these is the woolly oak leaf gall, produced by a tiny Cynipid wasp, Callirhytis lanata. This gall is usually attached to the mid-vein on the underside of an oak leaf, and looks like a ball of wool. It may be as large as three-fourths of an inch and is often bright pink or yellow in color, fading to light brown in the fall. Oak trees have lots of tannic acid in them (a defense which makes the tree unpalatable to herbivores), with the highest concentration found in oak galls. (The bitter taste is where the name “gall” originated.) It’s possible, since tannins are somewhat anti-microbial, high-tannin galls such as the woolly oak leaf gall may protect the larva against fungi and bacteria.

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