Woolly alder aphid (Prociphilus tessellatus)

Woolly Alder Aphid (Prociphilus tessellatus)

The Woolly Alder Aphid is a small but fascinating insect known for its dense covering of white, waxy filaments that give it a “woolly” appearance. Found across North America and parts of Europe, it has a unique two-host life cycle involving both alder trees and silver maple. These aphids are harmless to humans but can be an intriguing sight when large colonies appear on twigs or bark, often resembling mold or fluff.

🐜 Identification

• Size: ~2–3 mm (body length)
• Color: Bluish-grey to pale green or brown beneath thick, white, waxy filaments
• Appearance:
  • Dense cotton-like or fuzzy wax covering
  • Often found in large colonies on alder twigs or maple roots
  • Winged forms may appear in late summer or fall

When disturbed, they may release honeydew, which attracts ants and can promote sooty mold.

🌿 Host Plants & Habitat

Primary hosts (for overwintering and early spring):

• Silver maple (Acer saccharinum) — root feeders

Secondary hosts (summer):

• Alder trees (Alnus species), especially:
  • Speckled alder (Alnus incana)
  • Smooth alder (Alnus serrulata)

Habitat:

• Found in wetlands, stream banks, swamps, and lowland woods
• Most visible during late summer and fall, when colonies on alder twigs grow large and conspicuous

🔁 Life Cycle

The Woolly Alder Aphid has a complex, seasonal life cycle involving two host plants.

1. Spring: Eggs hatch on silver maple roots into wingless females.
2. Early summer: Aphids migrate to alder trees, forming colonies on twigs and branches.
3. Summer: Populations increase rapidly; winged aphids are eventually produced.
4. Fall: Winged aphids return to maple roots, where they mate and lay eggs that overwinter.

Some populations may stay entirely on alder if silver maples are not nearby.

🍽️ Feeding Behavior

• Feeding method: Piercing-sucking mouthparts extract sap from host plants.
• On alder, they feed on twigs and stems; on maple, they feed on roots.
• Excrete honeydew, a sugary waste product that:
  • Attracts ants (which may protect them)
  • Encourages the growth of black sooty mold on leaves or bark

Despite their feeding, they rarely cause significant damage to healthy trees.

🧬 Interesting Facts

• Often mistaken for fungus, mold, or cottonwood fluff due to their appearance.
• May form large white patches that move when disturbed — a startling sight for unsuspecting observers.
• Can be found in such high numbers that trees appear dusted in snow or fluff in mid-summer.
• Their waxy coating acts as a defense against predators and environmental stress.

🛡️ Impact & Management

• Ecological role:
  • Provide food for lady beetles, lacewings, hoverfly larvae, and other predators
  • Interact with ants, which “farm” them for honeydew
• Human and plant impact:
  • Generally non-damaging to host trees
  • No control needed unless infestations cause aesthetic or secondary issues (like mold)

Management (if necessary):

• Pruning infested branches
• Washing off colonies with a strong water spray
• Encouraging natural predators

The Woolly Alder Aphid (Prociphilus tessellatus) is a remarkable example of nature’s complexity—its unusual appearance, intricate life cycle, and interactions with ants and trees make it far more than just a “pest.” While visually dramatic, it plays a subtle role in forest and wetland ecosystems.

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