Studying Dragonfly Larvae

Dragonflies have two quite separate life stages: the larvae live in water, the adult insect is the supreme aerial acrobat and much harder to see and study. In general dragonfly larvae live for at least one year sometimes much longer; the adults are on the wing for no more than a few weeks. The adult insects that successfully breed probably amount to less than 5% of the larval population.

Larvae represent 98% of total biomass and are significant biological indicators, if you wish to study dragonflies in a serious way then inevitably you will need to study larvae.

This section of the website describes how you can find, study and breed out dragonfly larvae.

FINDING DRAGONFLY LARVAE
In temperate climates larvae are restricted to permanent bodies of water but in the tropics virtually any aquatic environment is utilised. Streams, rivers and lakes are obvious but temporary habitats such as tree holes, forest pools caused by the falling of a tree should always be examined. More rarely, species live in decaying vegetation and in forest leaf mould, even under damp logs, so do not ignore any wet or damp habitat. Some of our commonest tropical species even breed in puddles caused by lorry or car tracks and in South American a large number of species breed only in the flooded leaf axils of plants such a bromeliads.

Collecting dragonfly larvae is relatively simple using a small sieve, riddle or “shifter” to use a local African expression. Dragging the sieve through the mud or leaf litter at the bottom of a pool or stream is very effective. Don’t be afraid to sieve deep into the mud as many gomphids hide away in such areas to evade predators. Scooping up leaf litter can be productive if painstaking. Treeholes can be evacuated with a spoon or similar. A technique used for stream and rivers is to dam up the area at one point with a net then work up stream disturbing stones and gravel so that insects get washed down and trapped by the net.

Some of the rarer forest species live in seepages and around tree roots in streams. These insects can often be very difficult to locate. Sampling leaf litter in seepages can be a tedious business but worthwhile.

Another technique is to construct emergence traps which can be made of muslin or other fabric stretched over a wood frame and placed over probable emerging habitat. This has the added advantage of collecting both exuvia and the emerged imago for positive identification.

Dragonfly larvae have to shed their skins in order to grow. They do this between 10 and 15 times in a lifetime and each stage is called an instar. The older the larva the later its instar. The final instar before the adults emerge is termed F-0, the previous one is called F-1 and so on back to the egg.

Very young larvae (early instars) have very small wing cases but as they get older so the wing cases expand and cover more abdominal segments.

BREEDING DRAGONFLY LARVAE
Much can be learned from breeding out larvae. As well as structural information relating to the various instars, useful details of the insects behaviour and life can be observed. For tropical species, breeding is often the only way of collecting adult insects and possibly finding new species.

Having caught the specimens how do you look after them; You have three problems:

• Housing
• Feeding
• Emergence

Housing
Wherever possible you should try and simulate the insect’s natural environment. For example if you try and keep species that like to bury themselves in an empty pot then it is quite probablte that the hapless creature will quickly die of stress. I prefer to use aquaria.

A typical example is illustrated here. The aquarium is quite small and has the following features, right.

It has a built in filtration system which also aerates the water. This is important as any uneaten food can rot and pollute the system. Aeration helps to prevent this It has a built in lighting system which is ideal for photographing the larvae The base is covered with sand or fine gravel depending on the species you are breeding. I have some tanks with muddy substrate but when filling you need to leave this to settle for a long time. I always use plastic plants; the dragonflies are happy and they are maintenance free.

Macromia katae (right) from Hong Kong living happily amongst the plastic plants in the aquarium. Maintenance of the tank is mainly a question of topping up the water. Use rainwater if available or if tap water then let it stand for a few hours to eliminate chlorine etc.

Feeding
Feeding dragonfly larvae is always a problem, they will only eat live food and are voracious feeders. Collecting food can be fun for a while but becomes tiresome. In years past live food was readily available from aquarists; blood worms and daphnia readily available. Today, even around London, supplies are hard to come by and can be expensive.

The answer is to breed your own food supplies using a culture. I use whiteworms (Enchytraeus albidus) obtainable as a culture from Aquaculture Supplies www.aquaculturesupplies.co.uk

Follow these simple rules:

• I use plastic containers (large margaraine tubs are fine) with some holes punched in the top
• Fill the container about half full with potting compost. This should be peat and sand free because the worms hate acid conditions and cannot live in sand. Use organic material free of chemicals
• The compost should be very damp but not soggy. I use a small sprayer to keep the material damp
• Place your culture into the damp compost.
• I use white bread to feed the culture. Simply place it on the top of the compost having wet it with the sprayer first. When the bread becomes mouldy change it. I change the bread every five days or so.

You should keep the culture in the dark and at a temperature of between 15 and 20 degrees C. If the temperature goes much lower then the worms will not breed. At 27 degrees C the worms will die.

	A culture should be ready to use after about 10 weeks. A healthy whiteworm culture. The worms are clearly visible and ready for adding to the tanks. The bread is slightly mouldy and about to be changed. The plastic boxes housing the cultures are kept in a drawer to keep out the light.
A culture of this type lasts indefinitely or at least for years. Sometimes cultures become infected with small flies and other invertebrates but a good dosing with the sprayer keeps down pests.

Emergence
The emergence of the dragonfly is usually fairly easy to predict.

• It becomes less active
• It stops feeding
• It spends time partly above the water

In some species the wing cases appear to change and become light coloured. At this time you need to provide good emergence points. I use muslin or gauze which is placed directly into the tanks to provide ample emergence opportunity.

The green gauze goes into the water and to the bottom of the tank. In this case a muslin cage extends into the water and the tank base. The cage prevents the adult from escaping. Try not to disturb the insect whilst it is emerging because any disruption now could lead it to abort and die.

Familiar species can be released, but for tropical insects it is essential that the adult AND the exuvia are stored together for identification purposes. Both can be kept in a 70% alcohol solution and stored indefinitely.

Oxygastra curtisii A newly emerged female photographed against a background following emergence.

If you want any further information about any aspect of MSL work contact David Chelmick at dgc@macromia.com