Finding exuviae

Searching exuviae  can be very rewarding as you often will find exuviae of species which are difficult to find as adult. This is especially true for species of the family Gomphidae and Corduliidae of which the adults seldom come to the waterside while exuviae can be common.

Exuviae are always found near water. Look for them just above the surface to about 50 cm high. Some species may go further, even several metres far. Dragonflies prefer vertical substrates for emergence (e.g. plants, tree roots, steep banks, rock faces), but may also be found on horizontal substrates (floating plants, flat banks).

When you chase up a freshly emerged adult (which is still very pale, soft and shiny) from the waterside, try to catch it and look for the exuvia. Exuviae are nothing more than dried skin, and are therefore vulnerable. The legs easily break off when the exuvia is picked up: by splashing some water on it, the exuvia becomes moist and more flexible. Notes about the emergence site (place, height, substrate) can be useful.

Preserving exuviae

Exuviae must be stored dry. For storage, it is easiest to use photo film containers, as these are small, close tightly and are easy to come by, although their availability may diminish as the digital revolution progresses. Exuviae will often be moist after collecting, and when put in a closed container may become covered with fungi. Dry wet exuviae in the sun, or make a hole in the lid, so moisture can escape through it. Never store exuviae in alcohol, as they will become soft, soggy and battered.

Collecting larvae

Finding and catching larvae

Odonate nymphs are indicators of good water quality.

Many species are more easily found as larvae than as adult. An important purpose of searching larvae is rearing them to adult . Rearing will give you the opportunity to match the larva to the adult. A small metal kitchen sieve is often most suitable to find larvae in standing waters (between water weeds, small patches of leaf litter, under roots of riverside trees). In these situations it can be handy to put the leaf litter and plants in a white plastic container. This makes it easier to find the larvae among the litter. In running water it is more convenient to have a larger net with a more sturdy frame. A good method to catch larvae that live under rocks or burried in sand, is to place the net on the bottom and disturb the substrate (stones, gravel, sand) upstream from the net's opening with a rock or your feet. The disturbance will dislodge and expose the larvae, the current carries them into the net. Another good method is to put roots of riverside trees that hang in the water in the net and shake them vigorously. Such clumps of wet roots often harbour larvae of the family Calopterygidae.

Take notes on the larva's habitat: was it among aquatic plants, stones, buried in the mud etc.? For both identification and rearing purposes it is important to collect full-grown larvae. These can be recognised by the well-developed wing-sheaths: the wing-venation is clearly visible in them.

Transporting larvae

If you want to keep a larva alive there are three problems: drying, drowning and overheating. It is best to put the larva in a small, closed container. Do NOT put a larva in water, but rather in moist cotton wool or toilet paper, without or with very little free water and with plenty of air. Moss or other organic material can also be used, but only shortly as it may rot. Keeping the larvae cool (i.e. in a cool-box) at 5 to 10øC will extend their lifespan. Make sure that the larva remains moist
and oxygenated.

Rearing (breeding) larvae

Basically a tray, basin or aquarium with water will suffice as habitat for the larvae. Provide some substrate for the larvae (e.g. sand, detritus, water plants) and for emergence of the adult (e.g. a stick). Feed it with small aquatic invertebrates (mosquito larvae, cladocerans etc.). Keep the basin or aquarium out of the full sun. After emergence, it is essential that adult and exuviae are marked as belonging to the same individual!

Storing and labelling

Labelling is an important part of collecting (figure 7). It is important to make notes and labels every evening as this often becomes difficult after two days in the field. It is best to label with pencil as pen ink often fades.

Labelling
Essential information for any label or record is:
- name of collector/observer
- locality name (at least country, region and name of nearby town)
- collection/observation date
 

Other useful data are:
- coordinates
- habitat description (see box)
- altitude
- colours of living specimen

Describing habitats

The following list contains important factors to describe dragonfly habitats. Taking photographs of habitats is a good
way to communicate about habitat types.

1) type (pool, lake, paddy, river, stream, waterfall, seepage etc)
2) running (slow-moving, torrential etc.) or standing water
3) temporary or permanent water
4) size (i.e. diameter, depth)
5) forest cover
6) amount of sun and shade
7) turbidity of water (e.g. clear, blackwater, murky, silt-laden, chalky)
8) presence and type of aquatic vegetation (green algae, water lilies, emergent plants, water hyacinth)
9) presence and type of bank-side vegetation (reeds, bushes, grass etc.)
10) bottom substrate (e.g. mud, sand, gravel, rocks, detritus)
11) human disturbance (e.g. clearance of vegetation, erosion, damming, altered course)

Exuviae of Neurothemis terminata terminata (Ris, 1911) 紅蜻蜓 19 March 2007 7:18 AM Last 2 days were rainy and sunless days.  So it was an excitement to see a bright sunny morning when I woke up today. Needless to say, this morning is a day of activities for the dragonflies and their nymphs at this monsoon drain beside the car park. This newly emerged Neurothemis terminata terminata is one of the two newly emerged I am able to photographs before they made their maiden flight.

Exuviae of dragonflies are often found on vertical substrates like plants, tree roots, steep banks and rock faces.

All in a day's work.   Just in one morning I collected these 24 exuvia from 3 species all along this 50 meters drain. The smallest is Neurothemis terminata. which is rare in West Malaysia but common in Sabah. The medium and larger size are Diplacodes trivialis and Orthetrum sabina common in Asia.

Anax guttatus (Burmeister, 1839) 烏點晏蜓

Rhyothemis triangularis Kirby, 1889 三角蜻蜓

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INDEX OF DRAGONFLY