How do we explore insect biodiversity?
Finding them
Finding plant-inhabiting insects
- Try searching plants both by day and by night. Many species feed only at
night and hide by day.
- Look under leaves by getting down low and looking upwards. Keep an eye open for
fresh leaf damage.
- If you see the end of a branch drooping downwards, there is (or was) a tip-wilting bug sucking from the stem at the base of the drooping
portion.
- If you see little white balls of soap-sud-like froth on the plant, they are
probably made by spittle bugs (Hemiptera: Cercopidae and Aphrophoridae). Inside the froth
on the branch you will find the insect (often in the nymphal stage).
- Look for swollen stems and leaf bases caused by gall-forming insects.
- Check on flowers for nectar and pollen feeders. Check inside the flowers
(by taking them apart) for thrips (Thysanoptera).
- Open seed capsules and ripe fruit.
- By breaking open dead branches on shrubs and trees you will find a variety of
life including nesting ants, wood boring beetles, termites and various insects using cavities for shelter.
- Insects feeding in live wood are more difficult to locate but try search for exit
holes under bark or you might need to break open the live wood.
- Follow the activity of ants on the plant - they are often patrolling the plant
for honeydew producing bugs such as scale insects, aphids and
membracids.
- Dig into the soil to examine the root system of the plant and to find insects
feeding on the roots such as mealybugs, ground pearls, cycada nymphs.
Finding ground dwelling insects
- Look under rocks (always remember to return the rock to its original position
afterwards). Ground dwelling species often shelter under rocks and the best times to
search under rocks is when it is not too hot when the insects are using the underside of
the rock to warm up but the heat is not forcing them underground. Searching under rocks is
a particularly good way of finding ant nests.
- Set out pitfall traps. A cheap plastic coffee cup makes a good pitfall trap. Sink
it into the ground so that the rim is flush with the surface and fill it half way up with
a substance that will kill the insect when it falls in (e.g. soapy water) or kill and
preserve it (e.g. glycerol or propylene glycol). Cups with soapy water can only be left
for about three days before they need to be checked but cups with glycerol or propylene
glycol can be left for as long as a month (subject to flooding by rain - you can place a
hood over the up but this is no use if there is a heavy downpoar).
Finding leaf litter inhabiting insects
- Scrape away a patch of leaf litter to expose the soil beneath and search the soil
for movement. Pick up the insects you find with forceps and kill and store them in
ethanol.
- Sift the leaf litter through a coarse sieve (c 8-10 mm mesh size). Take the
sieved material and place in a Winkler Bag. Go here for
more info.
Finding subterranean insects
- Look under deaply embedded rocks.
- Dig holes, breaking open clods of soil to search for the insects.
- Mix together a sample of soil, sieve through course sieve and extract in
Winkler bag (see under leaf-inhabiting insects).
Finding insects that breed in carcasses.
- Looking on and under a dead animal on the ground can be very productive in terms
of finding insect families that you will find nowhere else. This is a stinky job and be
careful not to handle the dead animal with bare hands in case of disease.
- By putting out a freshly dead animal on the ground somewhere, you will be able to
track the succession of insects that feed on it. However, be aware that this carcass might
well get carried away by a scavenger and therefore it is usually necessary to place a
secure cage over the carcass.
Finding insects that breed in dung.
- Search through the dung and also dig in the soil beneath it. To prevent
being infected by some dreaded disease, don't handle the dung with bare hands (obvious
advice but just in case...).
Finding insects that live in freshwater.
- Look on the underside of submerged rocks for mayfly nymphs and caddis fly larvae
in their cases.
- In fast-flowing parts of a stream, check the tops of rocks for blackfly
(Simuliidae) larvae.
- Hold a net in the stream and disturb the rocks and gravel upstream of it -
insects get washed into the net.
- Sweep your butterfly net briskly through vegetation near the water so that
you dislodge the insects into the net.
Identifying them
Insects are such a diverse group of organisms that there is no one source you can rely
on to identify them. When you start out studying insects, you will be doing well if you
can just give it a family name.
The following sources will be useful to you for identifying the insects you find in
southern Africa:
-
This Biodiversity Explorer web site - if the insect is
common you might even get a species name. Alternatively, you should be able to work out
which order it belongs to and then follow suggested links.
-
Scholtz, C.H. & Holm, E. 1985. Insects of Southern Africa. Butterworths,
Durban.
This book keys out all southern African insects to family level and contains many
references to useful publications. However, be aware that it is geared for professionals
and to use the keys you will need a microscope.
-
Skaife, S.H. 1979. African Insect Life. C. Struik Publishers, Cape Town.
This book is a classic and contains superb photographs of selected species. It is
excellent for obtaining information on common species and is immensely readable. However,
it is not primarily an identification guide so you might well get frustrated trying to
identify your insect here.
-
If you are really serious about needing an authorative name for your mystery insect, you
might try having it identified by a professional in which case go to the list of local
specialists. However, be aware that you will probably be charged for the
identification and that specialists are not always able to find the time to do these
miscellaneous types of identifications. Also, it is important that you send the specialist
the specimens properly preserved and above all with proper labelling.
Collecting them
For an excellent book on insect collecting get:
Upton, M.S. 1991. Methods for collecting, preserving, and studying insects and allied
forms. The Australian Entomological Society Miscellaneous Publication No. 3, Brisbane.
Killing them
The easiest way to kill insects is to freeze them for about 24 hours. Alternatively,
make a killing bottle: put some tissue paper or cotton wool into a glass bottle and add a
little ethyl acetate (used as nail polish remover). Make sure there is some loose tissue
paper in the bottle for the insects to cling to - otherwise they tend to damage each
other. With practice, you will find out how much ethyl acetate is needed and how often the
bottle needs to be replenished with it. Some entomologists use cynide killing bottles but
this is dangerous stuff and not to be recommended.
Mounting them
This is quite a complicated subject which I can't deal with in too much detail here.
For more information, see the links below. However, let's make a summary of the main
mounting methods:
- Non-mounting of soft-bodied insects. Soft-bodied insects such as larvae should be
stored in 80% ethanol. You can also store adult insects in ethanol but this is usually not
a good idea for hairy insects, such as bees and flies, and scaly insects (the moths and
butterflies). Small insects such as fleas and lice can be kept indefinitely in ethanol
until they are mounted on slides.
- Direct pinning of specimens with insect pins. For beetles it should be through
the right-hand elytron so that the pin come out between the mid and hind legs. For
grasshoppers and crickets, it should be through the right posterior quarter of the
prothorax. For moths, butterflies, bees, wasps and flies, stick the pin throught the
centre of the specimen. If the insect has wings, set out both wings on a mounting board if
it is a moth, butterfly, cicada or neuropteran, making sure that the hind margin of the
front wings is perpendicular to the long axis of the body. Looking side-on, the wings
should not droop but be horizontal. Use a plentiful supply of pins and strips of smooth
tracing paper to keep them in place on the mounting board. For grasshoppers and crickets,
set out the left wings.
- Double pinning with minuten pins. Insects such as small flies can be mounted be
pinning them with a tiny insect pin called a minuten and then sticking the minuten through
a strip of dense foam which is then pinned through with a large insect pin.
- Point-mounting. An Insect such as an ant or small wasp can be glued to the tip of
an elongate triangular carboard point which is then attached to a normal sized insect pin.
- Card-mounting. Insect such as small beetles can be glued to a small rectangular
piece of cardboard which is then attached to a normal sized insect pin.
- Microscope slide mounting. Insects such as lice, fleas and scale insects
(Hemiptera), usually need to be mounted on microscope slides so that they can be
identified under a compound microscope.
Labelling them
It is very important to label your specimens accurately and with the essential
information. For pinned specimens, fix the label to the pin. For specimens preserved in
ethanol, place the label in the bottle with the specimen (don't stick it to the outside).
The following information is essential: country, province, precise locality, latitude
and longitude, date collected, and collector's name. It is also a good idea to include
whatever biological information you can on where you collected the insect (e.g.
'under rock in garden', or 'at light, West Coast Strandveld'). When you have collected a
lot of insects, it is a good idea to mass produce labels using a Word Processor and
a laser printer or an inkjet printer containing permadri ink (difficult to get hold of).
Laser printed labels aren't perfect as the toner can dissolve in ethanol if certain
organic solvents (leached from the specimen) are present. To make tiny insect labels on
the laser printer: (1) make columns 1.5 cm wide with 0.1 cm gap between each column; (2)
use a font size of somewhere from 3.8 to 5 point; (3) keep labels to no more than 6 lines
long. If you need more, make a second label to pin below the first; (4) print the labels
on acid-free card of about 120 g/m2.
Storing them in a collection
If you really get serious about collecting insects, you might eventually want to
purchase a wooden cabinet with glass-topped drawers at vast price. However, in the
beginning you can do well with a large flat plastic container bought from the
supermarket and with some sort of compressed foam or polystyrene stuck to the base. These
containers are good because they prevent pests such as museum beetles from getting in but
be careful not to put still-drying specimens in there because the moisture build up can
result in the specimens getting covered in fungus.
For
information on caring for a large collection, see S.A. Museum Entomology Collections
Manual (M. Cochrane)
Keeping them live
In order to keep insects alive, you need to keep them suplied with the right food.
Herbivorous insect larvae can be quite successfully reared in empty plastic coke bottles
that have been cut off at the base.
Links to collecting insects
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