This article appeared in the Evansville Courier & Press on November 11, 2001
Have you seen strings of white, waxy material floating in the air? I have, and apparently, so have a number of other people. Under normal circumstances, I think we'd just ignore this phenomenon, as it's not really all that troublesome. But, because of heightened tensions caused by the recent terrorist attacks, people are a little more anxious about this than I'd normally expect them to be.
Thanks to Dr. Lee Townsend of the University of Kentucky, we have determined that most of these floating threads are caused by woolly aphids, a common insect on silver maple and alder.
The woolly aphid is a sap feeder, and like most such insects, will produce large quantities of sticky honeydew as a waste product. This clear sticky substance soon covers the foliage and branches, as well as cars and lawn furniture underneath the tree. Often foliage becomes black from the sooty mold that grows on the honeydew. This is usually the major complaint against aphids in trees, and is generally not considered a major problem.
Unlike other aphids, the woolly aphid covers itself with white, wool-like waxy filaments. It's quite similar in appearance to mealy bugs, which you may have seen on your houseplants. Heavy populations of this insect can cause curling and yellowing of the leaves. The tree can also accumulate large amounts of the white, waxy filaments along the branches and stems.
Apparently, these white filaments are dislodged from the tree, most likely by wind. The filaments then float quite a distance, tangling with fences, windows, and shrubs quite a distance from the tree. You probably won't find any of the aphids in these tangled threads.
Woolly aphids have a complex life cycle, where they move between several different tree species. Woolly apple aphid, for example, alternates between elms and apples, hawthorns, and mountain ash. The woolly aphid we think is causing our mysterious threads hops between maple (especially silver maple) and alders.
The insect overwinters on maple bark in the egg stage or on alder in tightly clustered, wool-covered aphid colonies. Newly emerged aphids settle on the midvein of new maple leaves. These aphids reproduce asexually, producing very large colonies. The winged generation that develops flies to alder in July. Several generations may develop on alder, accompanied by production of large amounts of white waxy material. Some of the migrants fly back to the trunk and branches of maples, where they mate and produce eggs, one per aphid. Others remain on the alder in the adult stage.
Ballooning of spiders and other arthropods also can produce "floaters" in the air. "Ballooning" is a means of aerial dispersal that can be used by several spider species (remember that wonderful children's book, "Charlotte's Web?"). These floating silk strands (often 2 feet or greater in length), sometimes called "gossamers," are an ethereal sight on a sunny fall afternoon but they can cause concern at a time when anything out of the ordinary is seen in the air.
Ballooning spiders will move to the tops of vegetation or other high spots, stand on their "tiptoes", and release silk from the spinnerets at the end of their abdomen. When long enough, the silk will be captured by a breeze and the spider will be lifted into the air for a flight that can reach several hundred feet in the air and carry the 8-legged aeronaut several miles. Large numbers of spiders can be afloat at the same time, filling the air with silken strands that waft and twist gently in the breeze. They can catch on tree limbs, fences, or any other objects.
Ballooning activity occurs on warm days following cold nights. This sudden rise in temperature creates updrafts that provide ideal conditions for lift-off.
Several families of spiders that are common in Indiana are known to use silk to disperse. Some of the more common groups are wolf spiders, jumping spiders, and crab spiders. This mode of transport can be used by young spiderlings or adult males and females. It may be possible to find the spider on the silk.
For more information on unusual critters in the landscape, contact the Purdue Extension Service at (812) 435-5287, or e-mail me at larry.caplan@ces.purdue.edu .
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