Animal field guide
Common Water Flea
Daphnia pulex
A crustacean only a few millimetres long whose females can breed for generation after generation without males, each brood made of genetically identical daughters. When food runs short, crowding builds or days shorten, the same females begin producing sons and eggs that need fertilising.
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Get AnimalDexCommon Water Flea at a glance
Animal · North America · Still fresh water · Relatively common
Known for: Transparent oval carapace showing the gut and, Swims in jerky hops by rowing with large branched, Single large dark compound eye near the front of, Short pointed spine at the rear of the carapace
Animal field guide
Common Water Flea
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A crustacean only a few millimetres long whose females can breed for generation after generation without males, each brood made of genetically identical daughters. When food runs short, crowding builds or days shorten, the same females begin producing sons and eggs that need fertilising.
Native range
Natural range, not this capture location
Still fresh water: ponds, temporary pools, ditches and small lakes, especially fishless or fish-poor waters rich in algae. It swims in open water and along weedy margins.
Search near meAnimalDex stats
Dominance
1
Speed
3
Size
1
Intelligence
5
Rarity
24%
Total
34
Size scale
STEP 2 · PROVE IT
STEP 3 · BATTLE & FUSE
Understand the animal
Understand the Common Water Flea
Factual biology first: what this animal is like, where it lives, how it survives, and why those traits exist.
01
Introduction to Common Water Flea
A crustacean only a few millimetres long whose females can breed for generation after generation without males, each brood made of genetically identical daughters. When food runs short, crowding builds or days shorten, the same females begin producing sons and eggs that need fertilising.
How to identify a Common Water Flea
- Transparent oval carapace showing the gut and beating heart
- Swims in jerky hops by rowing with large branched antennae
- Single large dark compound eye near the front of the head
- Short pointed spine at the rear of the carapace
Why Common Water Flea are interesting
- In water low in oxygen it makes more haemoglobin and can turn pink or red.
- Its genome, published in 2011, was found to contain about 31,000 genes, more than the human genome.
- It is widely used to test water quality and the toxicity of chemicals, because it is sensitive and easy to rear.
- Some lineages have given up sex altogether and reproduce only by cloning, all year round.
- Its species name, pulex, is the Latin word for flea.
02
Adaptations and biological abilities
03
Why does Common Water Flea behave this way?
- Transparent oval carapace showing the gut and beating heart
- Swims in jerky hops by rowing with large branched antennae
- Single large dark compound eye near the front of the head
- Short pointed spine at the rear of the carapace
It has no sleep in the usual sense; its legs beat almost continuously, day and night, keeping food and oxygen flowing past the body.
04
Why Still fresh water?
Habitat: Still fresh water: ponds, temporary pools, ditches and small lakes, especially fishless or fish-poor waters rich in algae. It swims in open water and along weedy margins.
Native range: North America, Europe, Central Asia, East Asia
Native range
Natural range, not this specific capture location.
Still fresh water: ponds, temporary pools, ditches and small lakes, especially fishless or fish-poor waters rich in algae. It swims in open water and along weedy margins.
05
Why this diet?
A filter feeder: beating, leaf-like legs draw water through the carapace, and fine bristles sieve out algae, bacteria and organic particles, which are passed forward to the mouth.
06
Activity, rest, and lifespan
It has no sleep in the usual sense; its legs beat almost continuously, day and night, keeping food and oxygen flowing past the body.
Usually about one to two months, depending strongly on temperature: longer in cool water, shorter in warm.
07
Common Water Flea reproduction
Eggs develop in a brood chamber under the carapace, from a few to over twenty at a time, and the young leave after about two to three days as miniature adults. Fertilised eggs are sealed in a tough case that survives drying and freezing.
Males are smaller than females, with longer first antennae and hooked first legs used to clasp a female during mating.
08
Predators, threats, and defense
09
Conservation and rarity
Rarity: Relatively common · 24/100. AnimalDex canonical rarity score: 24/100, 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.
Speak to the animal
Speak to the Common Water Flea
It answers as itself: ask about how it lives, or bring it something of yours and hear what it would do, from its own Power.
Anonymous: 3/day. Signed-in: 10/day. Pro: 100/day.
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Compare the Common Water Flea
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Battled in the Arena
No one has taken a Common Water Flea into an Arena battle yet. Battles players fight with this animal in the AnimalDex app show up here.
Where to find them
Where to find Common Water Flea
To find Common Water Flea 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 north America, Europe, Central Asia, East Asia than by covering too much ground.
- Quiet marsh edges, reedbeds, river bends, or shallow wetland margins
- Sunlit logs, exposed branches, warm rocks, or regular perch sites used for scanning
- Protected habitat blocks within north America, Europe, Central Asia, East Asia
Scientific name
Daphnia pulex
Category
Animal
Habitat
Still fresh water: ponds, temporary pools, ditches and small lakes, especially fishless or fish-poor waters rich in algae. It swims in open water and along weedy margins.
Rarity
Relatively common · 24/100
Native range
North America, Europe, Central Asia, East Asia
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