Animal field guide
Alderfly
Sialis lutaria
The Alderfly spends nearly a year as a predatory larva in silt at the bottom of slow water, then a few days as a weak-flying adult that barely feeds. Almost all of its life is the waiting part, and that is where the work gets done.
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Get AnimalDexAlderfly at a glance
Animal · Native range keys: europe · Relatively common
Known for: Smoky dark brown wings held steeply roof-like over, Heavy, Long thread-like antennae and a broad head, Rests on waterside vegetation and stonework rather
Understand the animal
Understand the Alderfly
Factual biology first: what this animal is like, where it lives, how it survives, and why those traits exist.
01
Introduction to Alderfly
The Alderfly spends nearly a year as a predatory larva in silt at the bottom of slow water, then a few days as a weak-flying adult that barely feeds. Almost all of its life is the waiting part, and that is where the work gets done.
How to identify a Alderfly
- Smoky dark brown wings held steeply roof-like over the body
- Heavy, fluttering, reluctant flight over a few metres at most
- Long thread-like antennae and a broad head
- Rests on waterside vegetation and stonework rather than flying
Why Alderfly are interesting
- Larvae are fully aquatic predators with seven pairs of feathery abdominal gills, hunting midge larvae and worms in the silt for most of a year.
- The larva leaves the water to pupate in damp soil on the bank, so the species needs both the water and an undisturbed margin.
- Adults live only a few days to a couple of weeks and feed very little or not at all.
- Egg masses are laid in dense brown patches of several hundred on vegetation and structures directly above water, so the hatchlings drop straight in.
- Anglers imitate both the larva and the adult, and an alderfly hatch is a well-known trigger for surface feeding on lowland rivers.
02
Adaptations and biological abilities
03
Why does Alderfly behave this way?
- Smoky dark brown wings held steeply roof-like over the body
- Heavy, fluttering, reluctant flight over a few metres at most
- Long thread-like antennae and a broad head
- Rests on waterside vegetation and stonework rather than flying
Adults are sluggish by day and rest on vegetation, becoming most active in the late afternoon and evening; larvae hunt in the dark of the sediment regardless of time.
04
Why Native range keys: europe?
Habitat: Native range keys: europe, central_asia. Slow rivers, canals, lakes and ponds with soft silt beds and vegetated, undisturbed banks. Both halves are required — the silt for the long larval hunt, the bank for pupation.
Native range: Native range keys: europe, central_asia. Slow rivers, canals, lakes and ponds with soft silt beds and vegetated, undisturbed banks. Both halves are required — the silt for the long larval hunt, the bank for pupation.
Native range
Natural range, not this specific capture location.
Native range keys: europe, central_asia. Slow rivers, canals, lakes and ponds with soft silt beds and vegetated, undisturbed banks. Both halves are required — the silt for the long larval hunt, the bank for pupation.
05
Why this diet?
Larvae are active predators of midge larvae, worms and other soft-bodied invertebrates in the sediment. Adults barely feed at all; the entire energy budget for the flying stage was earned underwater.
06
Activity, rest, and lifespan
Adults are sluggish by day and rest on vegetation, becoming most active in the late afternoon and evening; larvae hunt in the dark of the sediment regardless of time.
Roughly one year in total, of which about eleven months are spent as a larva and only days to a fortnight as a winged adult.
07
Alderfly reproduction
Females lay dense brown egg masses of several hundred on leaves and stonework directly over water; larvae drop straight in on hatching and begin hunting immediately.
Males and females look alike; females are usually a little larger and heavier-bodied, most obviously when carrying eggs.
08
Predators, threats, and defense
Fish take both larvae and any adult that lands on the water, and birds take adults off waterside vegetation. The larva's defence is to stay in the silt, and the adult's is to be brief.
09
Conservation and rarity
Rarity: Relatively common · 20/100. AnimalDex canonical rarity score: 20/100, maintained by the live indexed species profile.
- Observe from a respectful distance and avoid changing the animal's behavior.
- Do not block feeding, shelter, nesting, or travel routes.
- Use a live camera capture without handling or staging wildlife.
Ask AnimalDex
Ask AnimalDex about the Alderfly
Ask about its biology, behavior, abilities, survival strategy, symbolism, or what its strategy can teach you. Answers stay grounded in this species page.
Anonymous: 3/day. Signed-in: 10/day. Pro: 30/day fair use.
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Where to find them
Where to find Alderfly
To find Alderfly in the wild, focus on the exact habitat patches that match its body design and daily behavior, not just the broad country where it exists. You usually do better by working one good piece of habitat inside native range keys: europe, central_asia. Slow rivers, canals, lakes and ponds with soft silt beds and vegetated, undisturbed banks. Both halves are required — the silt for the long larval hunt, the bank for pupation. than by covering too much ground.
- Quiet marsh edges, reedbeds, river bends, or shallow wetland margins
- Protected habitat blocks within native range keys: europe, central_asia. Slow rivers, canals, lakes and ponds with soft silt beds and vegetated, undisturbed banks. Both halves are required — the silt for the long larval hunt, the bank for pupation.
Animal field guide
Alderfly
The Alderfly spends nearly a year as a predatory larva in silt at the bottom of slow water, then a few days as a weak-flying adult that barely feeds. Almost all of its life is the waiting part, and that is where the work gets done.
Native range
Natural range, not this capture location
Native range keys: europe, central_asia. Slow rivers, canals, lakes and ponds with soft silt beds and vegetated, undisturbed banks. Both halves are required — the silt for the long larval hunt, the bank for pupation.
Search near meAnimalDex stats
Dominance
10
Speed
15
Size
5
Intelligence
12
Rarity
20%
Total
62
Size scale
Scientific name
Sialis lutaria
Category
Animal
Habitat
Native range keys: europe, central_asia. Slow rivers, canals, lakes and ponds with soft silt beds and vegetated, undisturbed banks. Both halves are required — the silt for the long larval hunt, the bank for pupation.
Rarity
Relatively common · 20/100
Native range
Native range keys: europe, central_asia. Slow rivers, canals, lakes and ponds with soft silt beds and vegetated, undisturbed banks. Both halves are required — the silt for the long larval hunt, the bank for pupation.
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