Direct Netting Techniques:
- A Short History of Netting:
It seems rather strange to us now that nets as we know them today took so long to develop as they seem second-nature to us and of 'common-sense' construction. However, in the early days of entomology the first 'popular' net was a cumbersome contraption known as the 'Clap Net'. This consisted of two poles, often between five and six feet in length, between which was attached a piece of muslin almost four feet tall by three feet wide. The net was used by holding a pole vertically in each hand and throwing them around the insect so that the poles met with a 'clap' on the opposite side. This left the insect surrounded by the muslin and whilst effective when it worked must have been ponderous to use and heavy to carry.
Another strange form of net which came to the fore, particularly with dipterists (fly fanciers) was the 'Scissors Net. This was shaped like a pair of scissors at the handle end but the blades where replaced by a diminutive bowl-shaped net on the lower blade and a flat 'lid' of net on the upper blade. By opening the 'scissors' and placing the 'blades' on either side of the insect it could then be caught by closing the scissors, the upper lid then knocking the insect into the lower net bowl and the lid closing and preventing the insects' escape.
Coming closer to home were the first 'sweep nets'. By this time, early 1900's, both the round net and the kite net had been developed and were constructed from brass tubing brazed to form a 'T' or 'Y' shaped handle and the net frame being made from soaked and bent bamboo - the net itself still being constructed from Muslin. As the interest of entomologists began to diversify into the more obscure insect groupings and away from the large and often gaudy butterflies and moths a need arose to be able to find insects living in dense vegetation. The nets then in use for catching butterflies were pressed into service by the expediency of substituting the muslin bags for ones constructed from canvas or hessian and doubling the thickness of the hem which went around the bamboo frame. This extra strengthening worked but the nets tended to break after one or two seasons.
Let us now have a look at a few of the more modern nets.
- Sweep Netting:
Sweep netting involves the use of a strong net for 'sweeping' through the low herbage, bushes, and even tree foliage, to dislodge the invertebrates resting or living there and to have them fall into the net bag. This all sounds very simple, but in practice there are a number of problems.
The first problem is mainly one of strength of construction. Lightly built cane-frame nets worked but their very lightness of construction caused many breakages as the net was forced through bramble thickets, was driven through dense grass tussocks or was thumped into bush and tree branches. Modern sweep nets tend to be made with metal rims, either spring steel or thick aluminium in order to cope with the physical stresses which this method can impose on the net frame.
The second problem is one of weight. Early sweep nets were light and modern ones, from the major manufacturers, come in both light-weight and much heavier construction patterns. Light weight nets are certainly easier to carry but to my mind are more tiring to use. This is due to the fact that they need to be 'pushed' through the herbage by muscular force - usually of the wrist and lower arm. This rapidly causes fatigue and necessitates frequent stoppages as well as being part of the reason for the development of blisters and chafed hands due to gripping the handle tightly to allow muscular force to be used to drive the net without it being wrenched from ones grasp. Heavier nets can be easier on the wrist as the net can be swung in an arc similar to a pendulum and the kinetic energy provided by this motion can be used to drive the net through the foliage thus lessening the amount of wrist and forearm muscle exertion required.
However, there are other considerations to take into account when purchasing, or even making, a sweep net for your own usage. The main one of these is the entrance to the net. Currently, two manufacturers hold the major portion of the sweep net market; these are Watkins & Doncaster (W&D) who distribute the heavier, all aluminium and steel net, and GB Nets (GBN) who distribute the lighter, aluminium-framed and wooden-handled net. The W&D net has its handle extended to run across the centre of the net opening to provide a rigid support for the spring-steel arms of the frame. This can, and does, get in the way of the operator and as a result many insect, especially those which can fly, escape before they can be tubed from inside the net. The GBN net has a rigid aluminium frame and this allows the operator to use a specific technique to prevent the escape of flying insects, this being: as soon as the net has stopped being driven through the vegetation it is placed over the operators head and shoulder(s) - this effectively sealing the entrance/exit for the insects. The operator can then push the apex of the net bag up and towards the light whereupon the flying insects will move towards the lightest spot and away from the operators face. This then allows the operator to tube the insects in the net at his/her own pace. This technique does have its own attendant problem as any experienced operator will have stories to tell. Should you have swept any bees, wasps or other large and stinging hymenoptera it can be very unnerving to suddenly and unexpectedly find them sharing a small space with you face, especially if they are flying towards you and are only a few inches away.
Another consideration is the shape of the net frame. A circular construction is often the easiest to achieve by the manufacturer and works well for general use being both strong and allowing for a large net size to maximise capture. However, some types of invertebrate, due to their very specificity of habitat usage, will never, or very rarely, be captured using one of these nets. For example: some families of small parasitic wasps live in very close proximity to the ground and at low levels within grass tussocks. Sweeping with a round framed net does not allow close enough contact with their habitat to result in their capture. But, if a net with flat sides to the frame is used (e.g. a triangular or hexagonal frame) then one of the flat sides can 'scrape' the ground and this close contact with the habitat niche will result in greater captures of the particular type of insect.
The final consideration for a sweep net is the construction of the
net bag. This may be made from cotton-sheeting, canvas, hessian or similar
material, or from a woven, man-made material (e.g. nylon, rayon, or
terylene). Cotton-sheeting provides a pleasant feel but when used in
damp or wet vegetation swiftly becomes too water-logged to be of any
use at all. Man-made material, depending upon thickness and openness
of weave can be less retentive of water in damp areas, is faster to
dry as it does not absorb water into its fibres, and can be longer/harder
wearing but usually does not feel as pleasant in use. The choice is
usually restricted by decisions made by a manufacturer but should you
have the necessary needlework skills these decisions can become your
won and can then be based upon personal preference or on the likely
conditions in which the net will be mainly used.
In use the sweep net should be swung backwards and forwards in an arc in front of the body as you walk through the grass and herbage. Every few paces the net should be examined for the catch and the insects or other invertebrates which are required for examination should be transferred to small glass or clear plastic tubes. Other creatures which are not required for examination should be carefully released! There is no excuse for wanton and unnecessary destruction or violent treatment of the animals which you catch. Sweep Nets should not be used in wet weather, particularly if they are fitted with canvas bags!! This is due to the fact that the bag will rapidly become waterlogged and as a consequence will soak all the captured invertebrates, rapidly turning them into something approaching a thick slurry at the bottom of the net. In most cases this will rapidly kill the insects as they suffocate with their spiracles filled with water and will almost certainly ruin any chances of obtaining recognisable specimens for retention.
Using sweep nets for the collection of invertebrates from bushes and trees requires a slightly different technique as the physical shock of hitting even small branches will prevent any rhythmical swing of the net. Try not to contact large branches and concentrate on sweeping the net through the smaller twigs where a better and smoother rhythm can be produced.
- Kite Netting:
A Kite Net is composed of a 'Y' shaped short handle, usually of brazed brass tubing, into the two open arms of which is inserted a frame of bent bamboo, or two aluminium rods connected by a piece of flexible plastic tubing. By unplugging one end of the frame the hem of a soft, tapering net bag, usually black netting, is threaded onto this frame, and once it is on, the frame is re-attached to the handle. The netting must be soft and non-abrasive in texture as this type of net is usually used for the capture of butterflies and moths. These animals have their wings and bodies covered with scales, much in the manner of roofing tiles on a pitched roof, and they are easily dislodged and rubbed off by course materials and rough handling. Without their scales the animals are difficult to identify and of little use in a reference collection - it should be noted here that the animals can, usually, be identified via genitalia dissection and, as a consequence, lack of scales should not prove a deterrent to identification when undertaking an invertebrate survey of a site.
Kite nets are used when one can see a specific insect, usually in flight, which one wishes to capture. The net should be swept up behind the insect and followed through on the stroke. As the stroke reaches its completion the net handle should be twisted to allow the long net bag to fold over the rim of the net frame. In this manner the insect will be enclosed in a closed off net bag and unable to escape. The insect should be extracted from the net by laying it on the ground and slipping a pill-box or collecting tube, depending upon the size of the insect, between the folded net and the frame and into the net bag. Once the insect has been caught in the pill-box or tube and the lid replaced the net can then be re-opened and the receptacle removed before venturing further.
The use of a kite net with some quarry can prove problematic. This includes the times when the insect is on the ground or is visiting a flower. When the insect is on the ground the net should be held with the handle in one hand and the tip of the net bag in the other. The net should then be brought down vertically over the insect whereupon the insect should fly vertically up into the outstretched net. This does sometimes work but one can not expect a 100% hit rate.
The problem of netting an insect from flowers is a more difficult one and one which is less likely to result in a satisfactory catch. A number of different approaches can be tried. The first duplicates the method used when an insect is on the ground as described above. This does however mean that you will have the plant inside the net along with the insect and this can cause damage to the insect and also impede your attempts at removing the insect from the net. The second method involves swinging the net from the side to just clip the top surface of the flower. Success here depends upon your accuracy with the net as well as the speed with which you can drive the net through the air - if the insect can take-off and accelerate in flight faster than you can move the net then you will miss it completely. If your accuracy is poor then you will find that you will chop the flower head from the plant and this may damage the insect beyond recognition. A third method is to frighten the insect into taking off from the flower and then netting it in the air above the plant - a risky procedure at the best of times.
- Kite Net Extensions on Beachcasters:
In some circumstances the very short handle which forms the base of the kite net, or even the longer handle of the round net, will be far too short for your purposes. One of these instances arises in March and early April when the day-flying moth, the Orange UnderWing Archiearis parthenias Linn., emerges. This moth flies around the tops of its larval foodplant, the Silver Birch tree, at heights of 12 to 30 feet in the spring sunshine. Consequently, to net it one needs a somewhat longer handle than normal. Recently, telescopic net handles have begun to appear on the market (see D. Henshaw in the Suppliers List in the Appendices), these being based upon the designs originally developed for angler's landing nets. Prior to this many different solutions have been used but one I have tried is taping a kite net to the top of a 15 foot long beachcaster fishing rod. This was distinctly unwieldy and such a contraption attracts a lot of attention from passers-by but it does work and it did the job, albeit with a bit of a wobble!
- Fly Nets:
Fly nets, or general nets, are usually round framed nets with a medium
to long handle and having a long, tapering net-bag of white terylene.
The small dark insects show-up better against the white net and the
terylene lasts a long time as it is a slippy material which gives it
a better chance of avoiding snagging on spiky vegetation.. The actual
frame size of the net may vary quite considerably depending upon taste
and the types of fly being sought. Net frames of 6 inches in diameter
up to 14 inches in diameter are readily available. The larger sizes
can be used for catching any insect on the wing and also as short term
sweep-nets in soft grasses, whilst the smaller sizes are used for catching
the smaller species of flies (e.g. picture-wing flies (Tephritidae)
within the close confines of hedges and thickets.
Surveying of ponds and other water courses for their invertebrate populations is, by its very nature, a wet and often muddy procedure. Means of extracting the creatures from their watery environment are needed and these can vary depending upon the types of life we are interested in capturing.
- Pond Nets:
For the larger life-forms, the device commonly called a 'pond-net' is the most suitable though this must have been designed for its specific usage and an ordinary /general net as described above will quickly break under the strains associated with 'pond dipping'.
A pond-net must be strong enough to deal with the combined weight water,
weed, animals and mud which is likely to be dredged out of the water
course. It requires a strong handle and the net itself must be made
of a material which will allow the water to drain quickly without allowing
the small animals to pass through the meshes.
One of the main problems with a pond-net is the very abrasive nature of the bottoms of water-courses; mud, sand or pebbles. As a consequence a better design incorporates a means of preventing the hem of the netting material from being abraded by the substrate. Nets incorporating this design feature can be purchased from GB Nets, Philip Harris Biological and from Watkins & Doncaster (see relevant addresses in the Suppliers listing in the Appendices).
Ancillary equipment needed will include a white tray, such as a photographic developing dish, into which the contents of the net may be deposited. This contents will then be searched through, by hand, for the various invertebrates living within it. Some clear water from the water body being investigated should be added to the white tray to allow the living organisms to swim away from the plant material and this often makes it easier to see them. A number of plastic tubes will also be required and into these specimens of the invertebrates caught can be transported back to the laboratory or to home for closer observation and possibly, for killing and preservation prior to identification.
In use the pond net should firstly be swept through the open water at the surface of the water body. The net should be moved backwards and forwards in a figure of eight motion turning the net at the end of each arc so that the open front of the net constantly faces the direction of movement - otherwise the animals caught in one arc will be swept out of the next on the following arc. This sweep of the net should include the actual surface of the water as many of the small animals live on the surface, supported by the surface tension. This net full should then be shaken out into the white tray for observation. Any animals required for further work should be placed into plastic tubes with a small piece of accompanying pond-weed to maintain a humid environment. Do not fill the tube with water - it rapidly depletes of oxygen due to bacterial action and then the animals will suffocate. Be careful not to place the tubes in the sunshine, they should be kept in the dark and preferably as cool as possible; keep them in canvas bag in the shade. The groups of animals most likely to be found include daphnia (water-fleas - a small crustacean), snails, pond-skaters, water-boatmen, whirligig beetles, diving beetles and both gnat and mosquito larvae.
The second sweep of the net should be addressed to the mid-water level including drives through pond-weed growth if such is present. This should obtain both free-swimming animals such as diving beetles, small fish, bloodworms, gnat larvae, mosquito larvae and water mites as well as those animals which are knocked out of the weed such as damselfly nymphs, dragonfly nymphs and beetle larvae.
The third and final sweep of the net should cover the lower water layers close to the bottom of the water body. If this substrate is of a hard nature such as compacted sand or pebbles then the net may scrape the bottom fairly vigorously however, if the bottom is composed of mud, then the net should only just scrape the surface of the substrate. If the mud layer is entered with the net a thick layer of black mud will line the inside of the net and will then be transferred to the white sorting tray. This will obscure any living creatures and make it very difficult to see what has been caught. Creatures found in this area will include leeches, worms, nematodes, fish, beetles, mayfly larvae, dragonfly larvae, damselfly larvae, snails and fish.
This regime of netting should be used around the water-body and particularly if different habitat niches can be readily identified from the bank (e.g. differing submerged water-plant communities, reed-beds, yellow-iris beds, open banks, rock cliffs, clay cliffs, etc.). Notes should be made, on the spot, as to the type of habitat each of the creatures caught appeared to occupy and these biological notes should eventually accompany any specimens retained for identification purposes or for eventual storage as voucher specimens.
- Small Sieves:
Some of the smaller water-bodies such as ditches, ephemeral ponds, or even rain-filled tractor ruts, motor-cycle tyre tracks and footprints can all provide interesting examples of living organisms which require water in their life-cycle. In fact many of these smaller water-bodies are essential for the reproduction of some animals which require periods of desiccation, as the water body dries out, for their eggs or pupae to mature. Obviously these areas of water are far too small to enable a standard pond-net to be used and it is in these tiny water bodies that the household tea-strainer, stainless-steel kitchen sieve or small aquarium net comes into its own. All of these devices can be pressed into service to provide a means of sampling these tiny pools for its animal life - it will be found that small or not these bodies can hold myriads of invertebrate life though most of them will have some form of flighted stage present in the life-cycle. These can include hosts of water beetles, diving beetles, whirligig beetles, water bugs, water scorpions, damselfly larvae, mayfly larvae, and mosquito and gnat larvae.
- Plankton Nets:
Very small invertebrates in the microscopic range (i.e. smaller than water-fleas (Daphnia) and Cyclops) need a special type of net to prevent them being lost through the meshes as they are in an ordinary pond net. The net is usually fairly small, normally less than 12 inches in diameter and the bag is made of bolting silk which has a very fine mesh. The net bag is between 1.5 feet and 3 feet in length, it tapers rapidly to its bottom extremity and at its end is not closed off as a normal net would be but is open to allow the attachment of a small plastic bottle. This plastic bottle is placed in the opening of the net and the net is either tied around the neck of the bottle with string or is fastened around the neck with strong rubber bands.
In use the net is drawn through the water at a sedate pace, and may pass around and between the vegetation. If the net is forced through the water too quickly the water pressure formed within the net will wash all of the collected plankton out of the bottle - the idea is to have the planktonic organisms collect in the bottle and to concentrate the numbers form a wide area of water. At the end of the sweep the contents of the bottle should be tipped into either other bottles or small stoppered plastic tubes for perusal under a microscope back at base. Again notes should be made of the types of habitat through which the net was passed and each sweep of the net should be addressed to specific habitat types. Creatures which may be found include: rotifers, desmids, diatoms, and many other forms of protozoa.
- Pond Dredging:
Whilst hand-nets of the types described above will probably provide the majority of the invertebrates for identification some animals tend to utilise deeper water and these can not be reached with the 3 to 6 feet of reach provided by a net handle. For these invertebrates it is necessary to make use of a either a dredge or a weed-drag.
A weed-drag is built like a small weighted anchor and is tied to a long length of rope. They can be constructed from pieces of steel bent and welded to form a cross or anchor shape. The drag is thrown out into the depths of the pond or lake, preferably to a bank of submerged plant growth which can be see from the bank, and it is allowed to sink. Once the drag has sunk to the bottom it is manually pulled back to the bank. On passing through the submerged weed-bed it will snag on the weeds and pull a largish clump back to the bank whence it can be transferred to a bucket and/or the white observation trays for examination. Different species of beetle and bug (e.g. diving beetles, water-boatmen, etc.) can be found in these deeper water weed-beds.
A pond-dredge is a small heavily weighted net with a bag of thick, strong material, which has a weighted, flat metal or wooden blade affixed along its bottom, front edge - a little like a very small trawling net used to catch bottom living fish in the sea. This, again, is cast out into the pond or lake and is slowly hauled back to the bank. The flat blade skims and scrapes the bottom of the pond or lake and traps the released organisms in the net bag. This can result in a thick mess of mud and stones which need to be carefully searched through on the bank or back at base. However, it can provide some of the more unusual deep water living invertebrates, particularly burrowing and tube-living worms.