Collecting Aquatic "Bugs"
"Disclaimer": Unfortunately being interested in aquatic bugs does not seem to be "cool" by public standards, or, for that matter by the professional biological community. Where as birding (Ornithology), plant surveying/collecting (Botany) and even studying butterflies (Lepidopterists) and beetles (Coleopterists) appear to be honourable hobbies for all ages (The latter two admittedly slightly more eccentric than the former! ), collecting and studying aquatic bugs is juvenilely referred to as "pond dipping". This conjures up images of a gaggle of bored public school aged kids armed with "butterfly" nets gathering around a harried and equally disinterested teacher/park worker looking into a tray of "swamp water" to see little things swimming about in order to fulfill curriculum requirements. Unless studying aquatic bugs can be associated with fly-fishing most would not consider it a respectable life long hobby let alone a viable career choice. Similarly in much of the scientific ecological/biological community "just identifying bugs" is worthy only of passing consideration and not a end on to itself.
Collecting aquatic insects/bugs requires only a limited amount of equipment:
- rubber boots, hip or chest waders
- a long handled net or kitchen sieve
- a shallow white pan or bottom of a white plastic pail
- an assortment of small liquid proof vials and jars
- field notebook
- 90% to 100% alcohol for specimens collected from water
- 70% to 80% alcohol for specimens collected in aerial sweeps
- field bag to carry things such as the vials, forceps, notebook etc.
- special aerial net
- a camera to record pictures of the site
- GPS unit for long/lat info
- fine meshed aquarium net
- turkey baster and/or eye dropper
These supplies can be made or purchased in various forms from retail hardware and drug stores or biological supply companies.
It is wise to go collecting with another person or a group. Not only does this provide a safety factor because slimy rocks are slippery but it also enables the collecting to be done more efficiently. One person can be making general collections with a dip net in the water while the other can be making aerial sweeps of the vegetation, turning over rocks and logs or investigating special microhabitats that may be present.
To make collections in ponds and along lake shores the net is passed through the weeds and open water. In streams and rivers the net can be held downstream of the feet and the feet shuffled to disturb pebbles and small stones. Insects on the stones will fall off and be carried by the current into the net. The net is then swirled in the water to remove fine silt and mud. The contents of the net are then dumped into the pan with about 2 cm of water in it. The insects will be seen crawling out of vegetation, sticks and pebbles and can be easily picked up with forceps or a small net and transferred to a vial or small jar with preservative.
Insects can also be collected from submerged logs and stones by hand.
I find one of the most useful collecting tools for shallow water is an ordinary kitchen sieve about 20 cm in diameter. The kitchen sieve can be swept through the vegetation, mud and gravel with no damage. I carry a snap lid 35 mm film canister or a hinged lid condiment container filled with alcohol and a pair of forceps tied around my neck with a string. I find that I can sweep the net through the water and quickly examine the material collected. When I find interesting specimens I open the lid of the container and put them in the alcohol and snap the lid back on. Periodically I transfer the specimens into a larger liquid proof sampling jar.
Aerial net sweeps of the shoreline vegetation will collect adults and adult swarms. The net contents are examined and the insects removed using a pair of forceps dipped in alcohol or a "pooter"/aspirator can be used to suck up the insects. There are a number of variations of pooters. In the simplest form a tube is put in your mouth and the insects are sucked up. A fine screen prevents the insect from being sucked into your mouth. In pooter A the insect(s) is sucked into a tube. Your finger is placed over the collecting end to keep the insects from escaping and then the insects are blown into a collecting jar. Another pooter type (B) sucks insects into a jar which can be be replaced when full. These methods are not very sanitary and can result in allergic reactions. An healthier and safer alternative is to attach a turkey baster (C) to the sucking end of pooter A. For pooter B a one way flow rubber bulb (for blowing dust off camera lenses) can be used by cutting a small diagonal slot to insert the blowing end of the bulb. Squeezing the bulb creates suction on the collecting tube.
Examining branches and rocks along the shore or sweeps of the water surface with a fine-meshed net will collect exuviae of many aquatic insects. Adults can also be collected directly from the water which they emerge from using various types of emegerence traps. This method not only provides many specimens in good condition but also information on the habitat/microhabitat the insect lives in, the timing of the adult emergence and if the collecting area of the trap is known, a rough estimate of the numbers emerging.
Many adult insects are attracted to lights, especially black lights, so checking lighted windows at night or looking around street lights can result in many interesting specimens. Of course biting flies, most of which are aquatic, can be collected from one's person as they attempt to feed using forceps or a pooter.
It is useful to make notes in a field note book describing the method of sampling and the sample location. Things like time, weather, water and air temperature, and other measurements if taken, and biological and habitat observations can all provide valuable information for future reference. Photographs of the habitat also provide useful information.
The alcohol should be changed about 24 to 48 hours after sampling to ensure the specimens will be thoroughly preserved and not start decomposing. If the jar has a large number of specimens or large specimens in it the alcohol may have to be changed a number of times to ensure proper preservation.
The next step is to sort the specimens into groups and begin to identify and study them. Small vials (2 to 3 drams in size) are ideal for storing sorted insects. Screw capped vials with plastic inner seals or neoprene/rubber stoppered vials work well. (Corks should not be used as they inevitably allow the alcohol to evaporate.) The sorted insects are preserved in 70% alcohol so they will not become brittle. A label of the location, collection date and name of collector is included in each of the vials with the name of the specimen if it has been identified.
Alcohol is a good all purpose preservative for most aquatic insects, although there are many, some extremely vile, concoctions that have been devised for particular groups. Ethyl alcohol (ethanol) seems to be a better bug preserver than isopropyl (proponal). (Note: All alcohols should be used in a well ventilated area to avoid inhaling the fumes. Methanol should NOT be used for health issues.) All alcohols cause colours to fade which makes it less than perfect for some groups such as adult dragonflies and damselflies. Also, adult mosquitoes and moths have their wings covered in scales which will wash off in alcohol so these groups should never be placed in liquid. For these groups pinning is a better way of preserving the specimens. The captured specimens are placed in a killing jar (This is an air tight jar that has absorbent material in the bottom with a small amount of ethyl acetate (finger nail polish remover) poured on it.) until they die. Another killing option is to place the insect sample in a freezer over night to kill them. Once killed the insects are sorted and an insect pin is placed through the thorax using a pinning block and then is placed (positioned if needed) on a styrofoam board until dry. A label is attached to the pinned specimen for reference.
No matter what method of preservation used the collections should be examined periodically to ensure the alcohol has not evaporated from the vials and that pinned specimens have not be infested with dermestid beetles which can reduce a pinned collection to dust in short order.
Taxonomic Rearing: A very worthwhile and rewarding activity is the "rearing" of immature insects. Only a small percentage of aquatic insects in the province can be identified to species in the larval stage so they have to be associated with the adult stage to be identified.
For this procedure mature larvae, or pupae, are collected and kept alive in a container of water; (one specimen/container). Rearing containers can be simple as plastic beverage cups with a loose fitting lid or pill bottles to more elaborate trays with mesh sided cages and aerators to provide oxygen and current to the larvae. Each group of aquatic insects requires different rearing conditions to successfully complete their life cycles. For some groups the larvae may need to be fed. With luck the larva will develop to maturity and the adult insect will emerge. The larval and pupal skins and the adult stage can then be preserved together and become a valuable record of the association as in the image to the left which has the larval and pupal skins along with the reared adult male.
Identifying many aquatic insects can be done with the unaided eye or a simple 10X hand lens. However, for most identifications lower than order or family some form of low powered microscope is very useful. A stereoscopic dissecting microscope capable of magnifications of 7 to 40 times is ideal for this type of work. (Microscopes are also great things to climb and perch on!!!) For most groups no elaborate specimen preparation is needed but other groups require special dissections and mounting on microscope slides to study them under high magnifications with the aid of a compound microscope.
Order and some family level identifications are relatively easy to do with some practise and a good guidebook. However, the majority of genus and species identifications require a great deal of experience and often a substantial library to do with accuracy.