I believe no other insect upstages Beech Bligh Aphids (Grylloprociphilus imbricator) in entertainment value. During a visit to a Lake County, OH, park last Thursday, Jim Chatfield and I came across a cluster of these engaging aphids shaking their woolly derrieres in what appeared to be a synchronous samba. All we needed was "(Shake, Shake, Shake) Shake Your Booty" by KC and the Sunshine Band blaring in the background to complete the effect.
The aphid nymphs enshroud themselves in a profuse mass of white, wool-like filaments. Large numbers of these "woolly aphids" will gather together in prominent "colonies" and when disturbed, the aphids pulse their posterior ends in unison. This peculiar behavior has earned the aphid the alternate common name of the "boogie-woogie aphid." To see what I mean, just Google "boogie-woogie aphid" to watch several YouTube videos.
It is speculated that this mass-wiggling distracts or dissuade predators and parasitoids from focusing on single individuals. However, research has shown that the nymphs are highly aggressive against predators. If the organized boogie-woogie doesn't work, the nymphs will mass-attack using their piercing-sucking mouthparts to inflict serious damage to no doubt perplexed predators. Perhaps the aphid's gyrations are actually a war dance! See "Dancing woolly aphids will probably stab you" in More Information below for the complete story.
The aphids are only found on the twigs and branches of American beech (Fagus grandifolia). Do not confuse them with the Woolly Beech Aphid (Phyllaphis fagi) which only occurs on European beech (F. sylvatica) and its cultivars.
Despite their sinister sounding name and penchant for appearing in large white masses, beech blight aphids cause little to no harm to the overall health of their beech host. However, we visited the Lake County park to observe and photograph symptoms of the enigmatic "beech leaf disease" and it occurred to us that a casual observer may link the disease symptoms to the aphids.
While the exact causal agent(s) for the disease remains unknown (stay tuned for an update BYGL Alert), it seems unlikely the aphids play a role. We only found one branch on one tree serving as a dance floor for the aphids. However, trees showing beech leaf disease symptoms were common throughout the park.
Beech blight aphids are prolific producers of honeydew. Even though the aphids are usually confined to just a few branches, it is common for sidewalks, parked cars, slow-moving gardeners, etc., beneath their gatherings to become covered in sticky goo. Indeed, aphid colonies are sometimes discovered by observing circular or semi-circular spots of sticky honeydew on hard surfaces beneath infested trees.
The sooty mold fungus, Scorias spongiosa (Ascomycete), has an obligate relationship with honeydew produced by beech bight aphids as well as a few other woolly aphids such as the Woolly Alder Aphid (a.k.a. Maple Blight Aphid) (Prociphilus tessellatus). Fungal growth begins like most sooty mold fungi; it grows as a dense, black, "fuzzy" mat on top of the honeydew.
However, over time, the mat thickens into a brownish, furry mass. Then the fungus progresses into a growth phase that is unlike most sooty molds; it produces a spongy, golden-yellow heap that may rise 1 - 2" or more above the leaf or twig surface. The odd-looking fungal growths look like nothing else that would commonly be associated with aphids or honeydew. It may also attract yellowjackets and bald-faced hornets in search of a sugary meal.
The fungus will grow anywhere that woolly aphid honeydew is deposited which may present a diagnostic challenge. It is common for thick fungal accretions to appear on the leaves and stems of understory plants that are not hosts to the aphids. During the winter, the fungal accretions turn coal black and may remain evident through much of next season. The black masses are sometimes mistaken for more serious plant problems such as Black Knot fungal galls that occur on members of the Prunus genus.