Alderfly Larva Identification Guide
A brown, filament-fringed aquatic larva with a single tail whip, found wriggling through the silty bottoms of ponds and slow streams.
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Key Visual Features
- Elongated body typically 0.5-1.2 inches (12-30 mm) long
- Brown to grayish-brown coloring, sometimes with subtle mottling
- Segmented abdomen lined with paired, tapering, unbranched lateral filaments along the sides, used as gills
- A single long, unbranched tail filament at the rear tip of the abdomen, distinguishing it from the paired hooked prolegs of a hellgrammite
- Six legs clustered near the head, used for crawling through sediment
- Head bears a pair of moderately sized jaws for grasping small prey, smaller than the pronounced sickle jaws of a diving beetle larva
- Overall softer, less armored appearance than a hellgrammite
Where and When You'll See It
Alderfly larvae are found burrowing through soft mud, silt, and organic debris at the bottom of ponds, lakes, and slow-moving streams. They favor calmer water with fine sediment rather than the fast, rocky riffles preferred by their larger dobsonfly relatives. They are active predators year-round in many climates, feeding on small invertebrates within the sediment, and are most often collected by disturbing bottom mud and debris during a stream or pond survey.
Similar-Looking Bugs
- Dobsonfly larva (hellgrammite): much larger and more heavily armored, with eight pairs of branched lateral filaments and paired hooked prolegs at the rear instead of a single tail filament.
- Fishfly larva: similar in shape but generally larger, often with small tufted gills at the base of the lateral filaments, which alderfly larvae lack.
- Diving beetle larva: has more prominent, curved sickle-shaped jaws and lacks the fringe of lateral filaments along the abdomen.
- Mayfly nymph: typically has three tail filaments instead of one, along with leaf-like or feathery gills along the abdomen rather than simple tapering filaments.
Quick ID Checklist
- Single, unbranched tail filament at the rear (not a pair of prolegs)
- Paired, unbranched lateral filaments along the abdomen
- Brown, moderately sized, segmented body up to about 1.2 inches long
- Six legs near the head
- Found burrowing through soft mud and sediment in calm ponds or slow streams
Frequently asked questions
How can I tell an alderfly larva from a hellgrammite?
The alderfly larva has a single unbranched tail filament at its rear end, while the hellgrammite (dobsonfly larva) has a pair of hooked prolegs there instead, along with a larger, more armored body and branched side filaments.
Where do alderfly larvae live?
They live in soft mud and silty sediment at the bottom of ponds, lakes, and slow-moving streams, generally avoiding the fast, rocky riffles favored by hellgrammites.
What do the filaments along an alderfly larva's body do?
The paired lateral filaments along the sides of the abdomen function as gills, helping the larva take up oxygen from the surrounding water.
How big does an alderfly larva get?
Most reach roughly 0.5 to 1.2 inches in length, noticeably smaller than the largest hellgrammites, which can exceed 2.5 inches.