Dragonfly and Nymph Collection and Observation Guide: Enjoying Aquatic Insects from Larvae to Emergence | ブリちょく
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Dragonfly and Nymph Collection and Observation Guide: Enjoying Aquatic Insects from Larvae to Emergence
Beginner's guide to raising dragonfly nymphs in an aquarium and observing their emergence. Covers collection sites, tank setup, feeding methods, and emergence support.
Key Takeaways
Beginner's guide to raising dragonfly nymphs in an aquarium and observing their emergence. Covers collection sites, tank setup, feeding methods, and emergence support.
Dragonflies are one of the insects that represent summer in Japan. Have you ever watched them dart swiftly through ponds and rivers and thought, "I'd like to raise one"? In fact, it is relatively easy to raise dragonfly nymphs called "yago" in an aquarium and observe the moment of emergence at home. This article explains in detail how to enjoy dragonflies, from collecting nymphs to observing them as adults.
Dragonfly Ecology and Species
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Dragonflies belong to the order Odonata and approximately 200 species inhabit Japan. They are broadly classified into two suborders: dragonflies that rest with wings open (Anisoptera) and damselflies that rest with wings closed (Zygoptera).
Typical species suitable for home rearing and observation:
- Shiokara dragonfly: Widely distributed throughout Japan. Nymphs are easiest to collect and ideal for beginners
- Gin-yanma: A large species. A beautiful dragonfly that flies with a swimming motion
- Oni-yanma: Japan's largest dragonfly. Its nymphs inhabit running water
- Mus-ji damselfly: A slender and graceful damselfly. Can be raised in small aquariums
- Asian damselfly: A versatile species found in urban ponds and waterways
Methods for Collecting Nymphs
Nymphs are carnivorous aquatic larvae. They can be collected from ponds, rivers, paddies, and irrigation channels from spring through summer.
Tools needed for collection
- Net with fine mesh
- Bucket (to hold collected nymphs)
- Dropper (for detailed work)
- Boots or waders
Collection tips
Quickly sweep the net along the bottom of the water where aquatic plants and fallen leaves accumulate. Since nymphs move quickly, transfer them immediately to a bucket after scooping them out. Pond edges and around reed (Phragmites australis) roots are easy collection spots.
Important considerations when collecting
- Check beforehand that collection is not prohibited under local natural park laws or municipal regulations
- Do not bring back invasive species (prohibited under the Invasive Alien Species Act)
- Insect collection may be prohibited within national parks
Setting Up a Rearing Environment
An aquarium is necessary for raising nymphs. While water conditions vary depending on species, the basic setup is common to all.
Equipment needed
- Aquarium (approximately 30 cm) or deep insect container
- Air pump and undergravel filter or sponge filter
- Bottom substrate (fine gravel or akadama soil)
- Aquatic plants (Japanese waterweed, Cabomba, etc.)
- Lid (essential to prevent escape and provide space for emergence)
Water quality and temperature
The ideal temperature range is 15-25°C. If room temperature exceeds 30°C in summer, cooling may be necessary. Remove chlorine from tap water before use. Perform water changes weekly, replacing one-third to one-half of the water.
Density and prevention of cannibalism
Nymphs are carnivorous and practice cannibalism. One container per nymph is ideal, but multiple nymphs can be kept together in a larger aquarium if plenty of aquatic plants are provided to create hiding spaces.
Feeding Methods
Nymphs possess a specialized predatory organ called the "lower jaw (mask)" that allows them to instantly snatch and consume prey.
Appropriate food
- Akamushi (Chironomid larvae): Most readily available and easy to portion according to nymph size. Frozen chironomid larvae are also acceptable
- Tubifex worms: High in nutrition and ideal for small nymphs
- Medaka fry and brine shrimp: Large nymphs can also be fed small fish
- Small crickets: Late-instar nymphs can also consume terrestrial insects
Feeding frequency
Feed once every two to three days as a general rule. Remove uneaten food promptly to prevent water deterioration.
Supporting Emergence and Observation Points
As nymphs approach their final instar, they increasingly surface. This is a sign that emergence is imminent.
Preparing for emergence
- Replace the aquarium lid with a mesh-covered lid with holes, or remove the lid entirely to provide emergence space
- Position a rod or wooden branch vertically against the aquarium wall for use as an emergence platform
- Adjust so that part of the emergence platform is exposed above the water surface for drying
Observing emergence
Emergence typically occurs at night or in the early morning. The nymph climbs onto the platform, its back splits, and the adult emerges. It takes 2-4 hours for the wings to dry completely. Avoid touching during emergence; simply observe.
Releasing adults
Once the wings have fully expanded, release the dragonfly into a natural environment near where it was collected. Rearing adults indoors is difficult because live insects must be continuously provided, so release is recommended.
Summary
The emergence of a dragonfly from a nymph is a precious opportunity to witness insect metamorphosis up close. Conduct collection while being mindful of the natural environment, and release the dragonfly to an appropriate location after rearing. It is an ideal subject for children's research projects and nature observation, and provides a valuable rearing experience for learning about dragonfly ecology.
