mistaken identity arlington macroinvertebrates · fingernet caddisflies movement: some snaps, but...

Mistaken IdentityArlington Macroinvertebrates

Lily WhitesellStormwater Outreach Specialist

Arlington County Stream Monitoring ProgramDepartment of Environmental Services – Office of Sustainability

This training is intended for ALL monitors at ALL skill levels: beginner,

intermediate and advanced. We’ll use common names for taxa and body

parts.

Review the classic movement patterns of the tricky macroinvertebrates

Build consistency in our identification protocol – when to use the microscopes,

take photos/samples, check with another monitor, and draw on references

Build consistency in the key characteristics and body parts we are using to

distinguish the macroinvertebrates

Goals and Takeaways

What are the three most

commonly found benthic

macroinvertebrates in Arlington

streams?

Small Minnow Mayfly

Midge

Netspinner Caddisfly

What are the most easily

confused macroinvertebrates in

Arlington streams?

Group 1: Midges, Netspinners, Fingernet CaddisfliesBonus: Riffle Beetle Larvae

Group 2: Small Minnow Mayfly, Narrowwing DamselflyBonus: Broadwing & Spreadwing Damselfly

Group 3: Aquatic worms, Leeches, Flatworms, Crane flies

Bonus: Scuds and Sowbugs

When is it hardest to identify

them?

• Small

• Colorless

• Early instars

• Recently molted

• Ambiguous movement

How can we tell them apart?

1. Use the microscopes

• Review when to use the microscopes for each type.

• Tiny specimen, colorless/transparent, ambiguous movement

• Cultivate your natural uncertainty (“I think… but let me check”)

• In doubt? Check the first few specimens of each type under the scopes.

2. Be consistent with ID criteria

• Ask others for consensus

• Refer to training and ID materials

• Take pictures!

Group 1:


Fingernet Caddisfly

Midges


Movement: head down, tail up, swishing abdomen & gills back and forth

Color: Head and first three thorax segments darker.

Often greenish, but this is not diagnostic! Small and early instar netspinners can be completely transparent.

6 legs come out from thorax segments

Feathery gills on abdomen!

https://www.flickr.com/photos/arlmonitoring/43230507014 0:12

https://www.flickr.com/photos/arlmonitoring/43044026465 0:24

When do you check under the microscope?

Small & tiny

Colorless/transparent! (Take pics)

Ambiguous movement: crawling, no tail swishes

https://www.flickr.com/photos/arlmonitoring/43230507014


Fingernet Caddisflies

Movement: some snaps, but not

repetitive like a midge. Often lifts

head up. Crawls using legs.

Color: Often yellowish with an

orange head & 1st thorax segment

(like midges, unlike netspinners)

Can be colorless, especially early

instars, but will often still have

darker head and first segment

6 legs come out from sides of thorax

Abdomen: SMOOTH! No feathery gills

https://www.flickr.com/photos/arlm

onitoring/43949314141/

When do you check under the

microscope?

Small fingernet caddisflies should

always be verified under a

microscope.

Take photos and send to Lily,

especially in cases of colorless/

transparent specimens.

https://www.flickr.com/photos/arlmonitoring/43949314141/

Midges

Movement, Free floating: Snapping or flipping head-to-tail, over and over.

Crawling: Uses nubby prolegs to scoot along.

Color: White, gray, clear, greenish, yellowish. Red.

Head darker (armored/hard cased)

Prolegs – two sets, one near head and one near end (unlike both caddisfly types)

Smooth abdomen (like fingernet, unlike netspinner)

Snapping:https://www.flickr.com/photos/arlmonitoring/43949788621

Scooting:https://www.flickr.com/photos/arlmonitoring/43901644672

When do you need to check under the microscope?

Ambiguous movement – scooting or “walking” on the bottom of the tray cube with very little snapping or flipping motion.

Midges are typically very small. Counter-intuitively, it’s good to double-check bigger midges.

At a site where you typically see both fingernet and netspinner caddisflies in abundance



Bottom end of Midges and Caddisflies

Midges

2 anal prolegs, tubules, setae

Brush hairs

Netspinner caddisfly

2 anal prolegs, each with a hook

More abundant hairs

Fingernet caddisfly

2 anal prolegs, each with a hook

1-2 small hairs on proleg hooks

Bonus: Riffle Beetles

Not typically found in Arlington

streams, frequently found at

reference site

Tapered, straight abdomen

Last segment tends to be longer

No anal prolegs

All segments sclerotized

Larvae may float in tray

Always check or take a picture in

Arlington

Questions on Group 1?

ID?

A

B

C

D

EF

G

ID?

Credit: Karen Thomas

ID?

A:

https://www.flickr.com/photos/arl

monitoring/43043971245 2:49

B:


monitoring/30080210668 0:09

Cross-eyed, anyone?

Any other questions before Group

2?



Group 2: Mayflies & Damselflies

Three tails and wingpads in Arlington

streams

Small Minnow Mayfly

Narrowwing Damselfly

Also: Broadwing Damselfly,

Spreadwing Damselfly

Small Minnow Mayflies

Tail spikes, not paddles

3rd tail can be hard to see, look

closely

Circular gills on abdomen

Tail often curved upwards

Flit or dart around the tub or cube

tray like minnows


monitoring/43949314141/


monitoring/43624146785

https://www.flickr.com/photos/arlmonitoring/43949314141/


Damselflies

Overview

Tail Paddles, not spikes

Most common damselfly in

Arlington is the Narrowwing

damselfly

Sometimes find Broadwing or


Above: Familiar Bluet, a narrowwing damselfly

Below: Ebony Jewelwing, a broadwing damselfly

Left: Spreadwing damselfly (slender spreadwing)

Spreadwing damselfly credit: Odonata Central https://www.odonatacentral.org/index.php/GalleryAction.viewImage/id/1906/taxon_id/43839

Narrowwing Damselflies

Most common damselfly in Arlington

Even antennae segments

Short, tapered abdomen

Movement: Walk and wiggle

Tails can be more rounded or angular ‘paddles’ – don’t be tricked!





Broadwing Damselfly

Narrowwing vs. Broadwing: Antennae segments

Broadwing: Long 1st antennae segment

Hair fringes on tail “paddles”

Long, slender abdomen


Less common

Antennae segments even

Slender abdomen

Tail veins in parallel lines

ID?

A

B

C

D

Group 3: Aquatic Worms, Leeches,

Flatworms

Plus: Crane flies

Aquatic worms

Segmented

Movement – swimmers, wiggly



Tiny, colorless (not a midge!)





Leech

Usually dark brownish color, can be colorless

Segmented (Annelida)

4+ eyespots, can be hard to see on brown specimens

Suction on end, then moves out from there, or scoots like an earthworm



Microscope?

Small, colorless



Leech variation

Flatworm

Dark brownish color

Eyespots with “cross-eyed” look

Triangular shaped head

Gliding movement

Can bunch up when touched







Crane flies Fleshy lobes at end

Colorless – can look like a midge

Big crane flies “swimming”:





Tiny crane flies









Crane flies

Welts vs. prolegs

Antocha vs. Dicranota

Antocha: creeping welts on

segments 2-7

Dicranota: prolegs on segments 3-7

Antocha is more common

Bonus Group: Scuds vs. Sowbugs

Sowbug has flattened body, like a roly-poly

Scud has squeezed body (side to side) like a mini-shrimp

Questions?

mistaken identity arlington macroinvertebrates · fingernet caddisflies movement: some snaps, but...

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