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Aphids

Elm Cockscomb Gall

Galls, abnormal plant growths caused by a variety of agents including insects, come in myriad sizes, shapes and colors.  One of the most distinct is the Elm Cockscomb Gall which is caused by an aphid (Colopha compressa).  These galls, named for their striking resemblance to a rooster’s comb, are maturing and turning red this time of year. 

For much of the summer the aphids responsible for these galls live underground sucking sap from grass roots.  In the fall a new (sexual) generation is born, takes to the air, mates and heads for an American Elm (Ulmus americana) tree where each female aphid lays a single egg under the bark.  In the spring the emerging nymphs seek young American Elm leaves on which to feed.  As they do so, the aphid nymphs emit compounds that result in the formation of galls.  Each nymph matures inside a gall and then reproduces asexually, giving birth to hundreds of young within the gall.  The mature, reproductive adult aphid dies and the young aphids develop into winged adults that exit the cockscomb gall through a slit on the undersurface of the leaf.  These aphids then go down into the soil to feed on the sap of roots until the next generation is born.

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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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Woolly Aphids

10-8-13 woolly aphid 001Woolly aphids are just that – aphids that have special glands that produce wax-like filaments which resemble white wool. When the “wool” is brushed aside, the dark aphid bodies below are apparent. Colonies of woolly aphids often congregate in cottony masses while sucking the sap of a host plant or tree, at which time they are somewhat camouflaged in that they can easily be mistaken for mold or a fungus. When woolly aphids take flight, the wax strands catch the wind and allow them to drift , allowing them to look more like seeds than edible prey.

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Green Lacewing Larvae Use Corpses as Camouflage

9-19-13 lacewing larva  232Green lacewings are aptly named for the prominent venation of the adults’ wings. Some species in this insect family even have “ears” in the larger veins that allow them to detect the ultrasonic sounds made by hunting bats. Lacewing larvae and adults are both predators of soft-bodied insects such as aphids. Larval lacewings have long, hollow mandibles with which they puncture prey and suck out the liquefied contents, leaving the woolly husks. Some species of lacewing larvae have hairy backs, and camouflage themselves when in the presence of woolly aphids by sticking aphid husks on these hairs. These “trash packets” camouflage the lacewing larvae from predators, including ants that would otherwise attack the larvae if they recognized that they were lacewings and not woolly aphids.

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Spiny Witch Hazel Galls

8-26-13  spiny witch hazel gall 045Aphids are responsible for the formation of two different galls (abnormal plant growths caused by insects, fungi, bacteria and viruses) on Witch Hazel (Hamamelis virginiana). A cone-shaped gall forms on leaves and a second type of gall covered with spiny points grows from branches. The latter gall, referred to as the Spiny Witch Hazel Gall, provides many aphids (Hamamelistes spinosus) with both food and shelter while they are developing inside the gall. (Their two-year life cycle involves birches as their next host.) The pictured Spiny Witch Hazel Gall has split open enough to allow ants to discover and have access to the aphids. Once the ants enter the gall, they stroke the resident aphids with their antennae, stimulating the aphids into producing droplets of tasty “honeydew” from the tips of their abdomens, which the ants find irresistible. In return, the ants protect the aphids from predators.

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