Aquatic Insects of the Sausal Creek Watershed
 
 
 

The organisms depicted in these photos are common in the watershed.  They live in the creek, and they are hard to see under normal conditions; they are usually heavily camouflaged.  To see them, choose a rock in a region of the creek that has fast, but not turbulent water flow, flip it over, and look for something moving.  Or, take a white bin and fill it ¼ full of creek water, and place your rock in the tub.  The insects will slowly come out of hiding, and it is much easier to see them on a white background.

Free-living caddisfly
Free-living caddisfly
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Midge larva
Midge larva
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Black Fly larva
Black Fly larva

(Order Diptera, Family Simuliidae) Larva is small, black beige or mottled, with a bowling-pin shape, often seen moving in a head-to-tail looping movement. The larval form often occurs in evenly-spaced ranks on rocks or leaves in rapidly flowing glides and riffles. It undergoes complete metamorphosis (egg, larva, pupa, adult), and pupates in July. The pupa looks like a tiny black slipper glued to the rocks. The adult is a serious agricultural pest.

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Dragonfly nymph
Dragonfly nymph

(Order Odonata, Family Aeshnidae) Brown, stubby abdomen, large eyes, short antennae, wing pads can be visibly on the thorax. Can get quite large! Flip this nymph over to see the plate-like labium (mouth part) on the ventral side, which whips out to capture prey. This very fast predator pulls water into its body through the anus, and then shoots the water out to move around near the bottom of the creek- a form of “jet propulsion”.

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Case-maker caddisfly
Case-maker caddisfly

(Order Tricoptera) Case-maker caddisflies build homes that they usually carry around with them. Cases can be made of sand, pebbles, woody material or leaves. The cases are glued together with silk- the caddisflies are related to butterflies, which also spin silk. These caddisfly larvae occupy a wide variety of habitats. They often orient themselves facing the current, so that water can flow through their cases. They undergo complete metamorphosis.

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Case builder caddisfly larva- sand
Case builder caddisfly larva- sand
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Stonefly nymph
Stonefly nymph

(Order Plecoptera) Stoneflies have three easily distinguished body segments: head, thorax and abdomen. There are often prominent wing-pads on the thorax. They prefer cool, clean water, and are found in sections of the creek under heavy canopy cover (shady areas), where they crawl around on leaves or woody debris, or under rocks. It shreds leaves, allowing the damaged leaves to be broken down by bacteria, and then feasts on the bacteria.

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Flatheaded mayfly nymph
Flatheaded mayfly nymph

(Order Ephemeroptera, family Heptageniidae) Small and brown, with an obviously flattened head and large, dark eyespots, very pretty abdominal gills, and two tails; most mayflies have three tails. The flattened shape allows this mayfly nymph to live in swiftly flowing waters, where it scrapes algae from the rocks. They undergo incomplete metamorphosis (egg, nymph, adult) and there are usually multiple generations per year.

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Diving beetle larva
Diving beetle larva

(Order Coleoptera, Family Dytiscidae) The diving beetle larvae live in the water or on vegetation in the water. Both the larva and adult are predators. The adults hunt in the water by diving underwater to capture prey. The larvae are slender, delicate-looking and have unusual eyespots. They catch their prey with their hook-like mandibles, inject digestive fluid and then suck out the liquefied contents of their prey.

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Planaria
Planaria

(Phylum Platyhelminthes, Class Turbellaria) This flatworm is ubiquitous in the creek, usually found in pools or very slow regions. It has distinctive eye-spots that give it a cross-eyed appearance. Body length: 3-25 mm Functional feeding group: scavenger Tolerance value: 8 (tolerant)

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Small minnow mayfly nymph
Small minnow mayfly nymph

(Order Ephemeroptera, Family Baetidae) Small, brown and torpedo-shaped, usually with visible wingpads, pretty, leaf-shaped abdominal gills, and three long tails. This nymph is ubiquitous in all sections of Sausal Creek, usually under rocks in glides and riffles. They are hard to see because they are fast and well-camouflaged. Many other insects, as well as trout, prey on them. There are usually multiple generations per year. They undergo incomplete metamorphosis (egg, nymph, adult).

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Water spider
Water spider

(Class Arachnida, Order Acariformes) Water spiders aren’t spiders- they are mites. They have eight legs, a head and a body, not the three body segments characteristic of insects, and can be blue, green, red or brown. They are found in pools or stagnant areas. The larval form is a parasite of other invertebrates. The adult is the form that is seen in the creek.

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Damselfly nymph
Damselfly nymph

(Order Odonata, Suborder Zygoptera, Family Coenagrionidae) Short antennae, large eyes, wing pads on the thorax, and three prominent leaf-like gills at the end of the abdomen. Flip this nymph over to observe the plate-like labium (mouth part) on the ventral side, which extends rapidly to capture prey. Damselflies are very active predators often found in quiet waters or stream edges, although some favor riffles. Undergoes incomplete metamorphosis (egg, nymph, adult).

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Crane Fly larva
Crane Fly larva

(Order Diptera, Family Tipulidae) Large, ugly, wrinkled larvae are found in soft, woody debris or sediment in pools or other slow-moving areas. The tipulids sometimes look like they are wearing turtleneck sweaters, because they pull their heads into their bodies. They have welts at the tail end, flaring out like a star. They undergo complete metamorphosis (egg, larva, pupa, adult) and turn into harmless, big-bodied insects with small wings, sometimes called “mosquito eaters”.

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Net spinner caddisfly larva
Net spinner caddisfly larva

(Order Tricoptera, Family Hydropsychidae) This caddisfly larva has dark head and thoracic plates, beige body, with lacy gills on the ventral surface, and a tuft of filaments at the end of the abdomen. The larva builds a case under a rock in a good current. It then spins a loose net in front of its cave which allows it to capture prey. It can survive in organic or nutrient pollution. It undergoes complete metamorphosis.

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Prong-gill mayfly nymph
Prong-gill mayfly nymph
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