Alderfly Larvae

Sialis spp.

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Photo of an alderfly larva among rocks and gravel in an aquarium.
Alderfly larvae resemble fishfly larvae but are usually much smaller. Note the 7 pairs of pointed appendages along the side of the abdomen.
Family

Sialidae (alderflies), in the order Megaloptera (alderflies, dobsonflies, fishflies)

Description

Alderfly larvae look a lot like fishflies and hellgrammites but are usually much smaller. Note that like fishflies, they lack gill tufts below the abdomen. There are 7 pairs of pointed appendages along the abdomen. The abdomen is tipped with a single tail filament that points straight back. Alderflies can be fairly light-colored, tan or brownish.

Like the larvae of fishflies and dobsonflies, alderflies have 3 pairs of jointed legs in the upper part of the body, with each leg tipped with a tiny, 2-parted pincer; and the mouthparts are large pincers.

Take care if handling alderfly larvae; they can pinch you with their stout mouthparts. Either hold them just behind the head, or use forceps to handle them.

Similar species: Fishfly larvae are usually larger and have 8 pairs of pointed, fleshy appendages along the abdomen; although, like alderflies, they lack external abdominal gill tufts, fishflies have a pair of short fleshy filaments and a pair of hooks at the abdomen tip. Hellgrammites (larval dobsonflies) are usually dark brown or black, usually much larger, and have 8 pairs of pointed, leglike appendages along the abdomen, each with a cottony or hairy gill tuft as the base. There is a pair of hooked, leglike appendages at the hind tip — not a single tail filament.

Size

Larval length: usually no more than 1 inch; varies with species.

Alderfly_larva_9-8-16.jpg

Photo of an alderfly larva swimming in a dish, with a gray background.
Alderfly Larva
Alderfly larvae resemble fishfly larvae, but instead of having pairs of fleshy tails, they have only a single tail pointing straight back.

Alderfly_larva_9-10-16.jpg

Photo of an alderfly larva swimming in a dish, showing head and mouthparts.
Alderfly Larva
Alderfly larvae are omnivorous or predatory, using their stout mouth pincers for grasping and chewing smaller aquatic invertebrates or organic materials.

alderfly.jpg

image of an Alderfly
Alderfly
Adult alderflies are usually black, dark brown, or gray. They look a lot like stoneflies but are more closely related to fishflies and dobsonflies. They are generally poor fliers.
Habitat and conservation

Different species prefer different types of aquatic habitats. The larvae of some alderflies prefer slow-moving, detritus-littered waters, such as lakes and ponds, while others prefer silt-bottomed pools in quieter sections of rivers and streams. Some can tolerate polluted waters. The short-lived adults are usually found among vegetation near water.

Foods

Alderfly larvae, depending on species, are omnivorous or predatory, using their stout mouth pincers for grasping and chewing smaller aquatic invertebrates or organic materials. Alderflies generally do not eat during their brief time as flying adults.

Distribution in Missouri

Statewide.

Status

Alderflies are one of two families in the insect order Megaloptera (the name means “large wings”). The other family in this order comprises the fishflies and dobsonflies. In the past, megalopteran insects were considered part of a much larger order Neuroptera (“nerve-winged” or “net-winged” insects); today Neuroptera is a smaller group, including lacewings, mantidflies, antlions, and owlflies.

Life cycle

Like many other insects with aquatic larvae, most of an alderfly’s life is spent in water, growing through immature stages, with only a brief period experienced as a winged adult. Females lay eggs on leaves or branches near water, and the young move into the water soon after hatching. As aquatic larvae they eat, grow, and molt. They crawl out of water to pupate in a sheltered place; sometimes in the soil, sometimes in rotting wood or behind loose bark.

Human connections

Alderfly larvae, like many other aquatic invertebrates, provide food for growing fish and are therefore important for healthy fisheries.

Ecosystem connections

Alderfly larvae eat smaller invertebrates and are in turn eaten by larger aquatic organisms, such as crayfish and fish. They are also eaten by the larvae of their close relatives, the fishflies, which are larger. If they survive to adulthood, they can become food for a variety of insectivorous animals such as flycatching birds and spiders.