Spiny water flea

Bythotrephes longimanus · Aquatic life

Under the microscope · Photo: Dmitry Kulakov / CC BY

InvasiveCladoceran (water flea)

Also called Spiny waterflea, Bythotrephes longimanus, Bythotrephes cederstroemi

State listing

Idaho: Prohibited invasive species

How to identify Spiny water flea

Large water flea about 0.5 inch long including the tail
Very long, straight tail spine with one to four pairs of barbs
Single large dark eye
Clumps on fishing lines look like wet cotton with tiny black dots

Similar species

Fishhook water flea has a tail spine that ends in a hooked loop; native Leptodora has no long tail spine.

Profile

Season	Summer and fall; hatches from resting eggs.
Depth	Open water
How it spreads or reproduces	Females clone themselves; resting eggs survive in mud, bilge water, bait buckets and on fishing line and anchor ropes
Habitat	Large lakes and reservoirs; not known from Idaho, Oregon or Wyoming. Watch for it on boats and gear coming from the Great Lakes region.

Why it matters in a lake

An invasive predator that eats native zooplankton and can disrupt the food web and fishing. Its spine makes it hard for small fish to eat. Clean, drain and dry boats and gear.