COLLECTING INSECTS
Entomology 116 – Insect Identification
| David L. Keith | Tiffany Heng-Moss |
| Professor of Entomology | Asst.Professor of Entomology |
Where and How to Collect Insects
Insects feed on the leaves, stems, roots, flowers and
fruit of many horticultural plants, producing directly visible damage or
symptoms. Examine plants closely. Look for holes in leaves or ragged leaves
near the ends of branches. Turn leaves
over to see for sure, especially if you spot any leaf discoloration or
stippling patterns. Also check for ant
activity – they often tend aphids or scale insects whose honeydew (sugary
excrement) they love. Look for holes in
stems – evidence of boring insect
activity and insect frass (excrement).
Plants damaged by soil insects or stem-borers may wilt in the heat of
day and recover somewhat in the evening when the sun goes down. Pull damaged plants and closely examine root
systems for signs of insect attack.
The best insect collecting is often in diverse
habitats. A vegetable or flower garden
or landscaped facility such as a park, arboretum or zoo will usually have
multiple plantings of many different types of plants. But make sure that you have permission to
collect first. Note that it is illegal
to collect in a federally sponsored facility or national park without a
collecting permit. Always be careful not
to damage plants when collecting. You
shouldn’t cause more damage to the plantings than do the pests themselves. Be reasonable and don’t hack off side
branches, limbs of trees or entire shrubs or flowers unless they are not
salvageable (dead or dying). When
collecting insects, don’t forget to dig
in soil. Most plants have a
characteristic group of “specialist” insects which feed on them. Other insects may be more general feeders,
attacking a large group of plants. Chop
into a dying tree or rotting log to discover some interesting specimens.
.
Insect Collecting Equipment
The basic equipment necessary for field collecting is an
insect net, one or more storage boxes, insect nets, pins, pinning blocks,
spreading boards, light and pitfall traps, killing jars, killing and preserving
chemicals, several vials of assorted sizes, plastic bags and assorted
containers. A collecting bag (roughly
14" x 18") made of canvas, muslin or other strong material is helpful
to carry equipment, plant cuttings and insects when out in the field. These supplies can be obtained by direct
order from one or more biological supply houses such as BioQuip (310-324-0620
or e-mail: bioquip@aol.com).
The Killing Jar
When
placed in the killing jar, insects often close their spiracles, but eventually
they must open them. The process may
take several minutes for smaller insects or up to a half hour or more for
larger specimens. Because large,
hard-bodied insects such as beetles die slowly and may damage other insects
placed in the same killing jar, you will need more than one jar. Also, you may break or lose one of your jars.
It is possible to make suitable killing jars with nearly
any jar used for jam or jelly and baby food jars are especially handy. Do not use plastic containers, because the
chemical killing agent may damage them. At least one large (i.e. pint or quart
size) jar would be helpful for larger specimens.
In
the bottom of each jar, place about 1 to 1 1/2 inches of absorbent material,
such as cotton, shredded newspaper, Plaster of Paris or wood fiber (sawdust).
If Plaster of Paris is used, pour it about 1 inch deep and allow it to dry for
at least 48 hours before use. With paper-or fiber-filled jars, cut a cardboard
circle just slightly larger than the inside diameter of the jar and push it
into the opening against the plaster in the bottom. Wrap the outside bottom
third of each jar with masking tape to prevent cuts in case the jar is broken.
Attach a label that says POISON to each jar and store the jars out of reach of
children (or irresponsible adults) until you are ready to go collecting.
The
killing jar is now ready to charge with a killing agent. Pour enough ethyl acetate (a tablespoon or
so) into the killing jar to thoroughly wet the dry, absorbent plaster. Use a bit more if the plaster will absorb
it. Pour off any excess into the
original container. Do not use too much
or you may “wet” and damage insects that you collect. Turn the lid on tightly
to prevent loss of fumes. As the killing jar is used, it will lose its strength
so the killing agent must be replenished from time to time. Tear up some strips of paper, crumple them
slightly and place them in each jar.
This will help to prevent insects from damaging one another.
Pinching the thorax of large butterflies or moths before
placing them in the killing jar will prevent them from flopping around and
damaging the wings. Squeeze them for 20-30 seconds between thumb and index
finger and put them in the killing jar. This procedure stuns the insects so
they do not flutter once inside the jar. Remove butterflies and moths from the
killing jar fairly soon so their wings do not become soaked with killing agent.
If a killing jar is not available, freezing is another
way to kill insects. Simply place your specimens in a plastic bag (the Zip-Lock
kind is nice) or small jar and put them in the freezer for an hour or two. Do
not handle them again until they are thawed or legs and antennae may break. And don’t forget them in the freezer. Insects, like food, left too long in the
freezer for several days or weeks will desiccate and remain dry and stiff, even
when thawed. If pinned when dry, these
insects will break during handling and wings, especially of Lepidoptera, will
be impossible to spread. Remember that
specimen quality is an important consideration in grading insect collections.
Using the Relaxing Jar
We recognize that while insects should be pinned on the
same day they were collected, this is not always possible. So before pinning these specimens left in
the killing jar or freezer too long, to restore their flexibility, it is
necessary to “relax” them. By placing
them in a relaxing jar at high humidity for a few days we can restore their
flexibility enough to allow pinning without damage to the specimens.
Relaxing is always a risky process and, if carelessly
done, the specimens may be ruined.
A relaxing jar is easy to
make. Simply use another baby food or
larger jar as the relaxer. Place some absorbent material such as newspaper,
sand or cotton in the bottom and cut a blotting paper disk to fit tightly
inside. Moisten the material with water and add a drop or two of ethyl
acetate, phenol, Lysol or laundry beach
(Hi-Lex, Purex, Clorox) to prevent mold. Place insects on the paper,
close the jar tightly and let it sit for about 2-3 days. Check the jar. If the
insects are flexible, mount them immediately. If the specimens are still too
stiff, keep them in the relaxer for a few more days, but watch them carefully.
Insects will mold and decompose if held in the 
relaxer too long.
Using a Collecting Net
Aerial nets for collecting flying insects can be ordered
or made at home from a 4-foot length of doweling, about 4 feet of heavy wire
and a half yard or so of sheer nylon or orlon netting. Grooves are cut across one end of the handle,
then a one-half inch deep hole is bored on one side of the handle (in the
groove) three inches from the end. A second hole is bored one-half inch deep in
the opposite groove four inches from the end.
A four foot length of heavy wire is bent into a hoop and attached to the
handle by a 4-inch aluminum slip collar, which holds the wire hoop in place.
The
bag, once hemmed and attached to the hoop, is about one foot in diameter, two
to three feet long and tapered to a point. The bag is slipped onto the wire
hoop before it is attached to the handle.
A muslin or denim band is usually sewn over the hoop end of the bag to
make the net last longer. Sweeping or
beating nets are made like aerial nets. However, the net bag is constructed of
strong muslin material instead of the lighter netting. These heavier duty nets
are used to collect insects from grass, trees and shrubs by swinging the net
through heavy foliage. Thus, these nets
are sometimes referred to as “beating” or “sweeping” nets. The sweeping net is widely used to sample
insect populations in standing field crops such as alfalfa, wheat and
soybeans. As the surveyor walks through
the crop, the net is swung in an arc a specified number of times – e.g. 10, 20,
50, 100, etc. Done at several locations
over time in a field, and the results totaled, a reasonable assessment of the
pest population can be made, compared with economic thresholds and
management/control decisions made.
Other Collecting Equipment and How To Use It
Aspirator. The aspirator is a suction device for
collecting small insects which are difficult (or hazardous) to capture with the
fingers or with an insect net. Basically, it consists of a large glass or
plastic vial, a length of flexible rubber tubing, some rigid plastic or metal
tubing and a rubber stopper with 2 holes cut in it to receiving the tubing. A
small piece of cheesecloth or fine metal screen serves to seal the suction tube
on the inside so that insects are not sucked into the mouth. Bear in mind that if you collect ants, you
may not suck the ants through the fine mesh, but their defensive secretion
(formic acid) can give you a nasty mouthful, especially if the ants are large
and numerous. This experience is
guaranteed to clear your sinuses.
To make an aspirator, bend the two lengths of rigid
tubing and fit the tubes into a rubber stopper. The long tube should extend
down to within about one inch of the bottom of the vial when it is in proper
position. Attach the small piece of cheesecloth or metal screen to the short
piece of tubing with solder, glue or a rubber band. (This is to prevent you
from sucking several bugs or bits of dirt into your mouth when you are using
the aspirator.) Now attach the rubber
tube to the short piece of rigid tubing.
To use the device, just place the long tube beside a
small insect, put the rubber tube into your mouth and suck sharply. With a bit
of practice, you will find that this is an excellent way to collect smaller
insects with ease.
Light traps. Many types of insects are attracted
to light and can be captured there by hand. A light trap offers the advantage
that it will continue to trap specimens without being constantly watched by the
collector. Insects are quite sensitive
to different types of light; therefore, more of certain types can be captured
with “black” (or ultraviolet) light as opposed to the regular “white” light
given off by most standard light bulbs. The difference in attractiveness of the
two types of light is due to the wave lengths produced by the two kinds of
bulbs. Black light consists mainly of the shorter wave lengths which are more
attractive to night-flying moths, flies and beetles. White light bulbs
(producing mostly longer wave lengths) attract some moths and other insects,
but not as many as a black light. Simply
turning your home entry lights on or standing under a street light or in your
car headlights often produces many specimens, including many horticultural pest
insects. Many of the night-flying
cutworm moths can be captured when feeding on various flowers during evening
hours.
All
that is needed to make a simple light trap is a battery-operated lantern or an
automobile trouble light with a 100-watt or larger bulb, a large metal funnel
(you can also make one of plastic sheeting, but remember this is flammable) and
a wide mouth jar or a large tin fruit juice can. Hang the light outdoors away from the
buildings, in a sheltered place, near a power source, if needed and no more
than 4 feet off the ground. Construct a
wire framework to support the lantern or suspended bulb, funnel and trap can.
Make sure that the end of the collecting funnel is large enough to allow larger
insects to pass through. Place some crumpled newspaper in the bottom of the can
(about 2 inches deep) and lightly wet it with killing solution. Start the trap
at dusk and empty it in the morning. A
simpler trap setup is to prop up a white sheet to serve as a reflecting
surface, then to sit a lantern in front of it on a chair or stool. Collect the insects attracted to the sheet as
they land on the surface. Blacklights
are made in the same form as regular fluorescent tube lights and can be
operated in similar types of fixtures.
Do not look directly at the blacklight bulb, because ultraviolet light
can damage eyes. Night-flying insects
seem to be more often attracted to light traps placed in sheltered areas (i.e.
protected from wind by trees) than those in more open areas.
Pitfall
trap.
A pitfall trap will catch many ground beetles and other insects that
live on or in the soil. It consists of a trap can that is buried in the soil,
level with the rim so that insects attracted to it will fall in. Once inside,
it is difficult for them to get out. An attractive bait in the bottom will
increase the drawing power of the trap. Use pieces of spoiled fruit,
vegetables, excrement or meat. Cover the trap with a board placed on small
stones so insects can crawl under it and into the can. This arrangement will
protect the trap from wind and rain, but allow access to the insects you want
to catch. It will also help to hold insects inside the trap once they are
caught. Remove the insects that you catch each morning.
PRESERVING INSECTS
Hard-Bodied Insects
Since insects have a hard shell or exoskeleton and all of
the soft parts are on the inside, they tend to keep rather well after drying,
even for long periods of time. Only a small amount of maintenance is necessary
to keep them in good condition. Many
specimens in museums today are over one hundred years old and look just as they
did on the day they were collected.
Certain types of insects may fade, but others hold their colors
indefinitely. If you want to study
insects in the winter, you must work with collections of dead insects or with
living laboratory-reared material.
Remember that dead, pinned insects are very brittle and delicate. They must be handled very carefully and never
jarred, dropped or touched directly.
Specimens whose legs, antennae and wings are broken and lost are
essentially worthless. Also, damaged
specimens will not be graded as highly in your insect collection.
Soft-Bodied Insects
Many types of insects, including aphids, springtails,
thrips, mayflies or silverfish, are soft-bodied and cannot be pinned
successfully. The same is true of many
immature insects such as caterpillars, beetle and wasp larvae and others. If placed on pins, most soft-bodied insects
will shrivel or decompose. Such insects
must be preserved in liquids in rubber-stoppered glass vials. However, prior to preserving soft-bodied
specimens for the long term, their color must be “fixed” or they may fade in
some cases or blacken in others. The
“fixing” process prevents, reduces or delays color change.
For
the long term, insects are preserved in ethyl alcohol, usually of about 70
percent concentration (70% alcohol, 30% water).
Isopropyl alcohol can also be used, but with less success. Over time, alcohol at lesser dilutions, i.e.
stronger solutions can cause colors of specimens to darken and bodies to
shrivel. Remember that alcohol is a
dehydrator -- it removes water. These
problems can be largely prevented in either of two ways. The best way is to “fix” the insect tissues
and color by killing the specimens in boiling water. For smaller specimens, simply dip them in
boiling water for about 30 seconds and then transfer them to 70 percent
alcohol. Use more extended periods for
large-bodied insects.
The most preferred method, often used for caterpillars
and other soft-bodied larvae, is to kill the insects in a special fixing
solution called K.A.A.D. mixture. This solution is made by mixing one part of
refined kerosene, two parts of glacial acetic acid (a weak acid), ten parts of
95 percent alcohol and one part of dioxane.
A good feature of the K.A.A.D. solution is that it causes soft-bodied
larvae to uncurl, distend and swell, expanding the tissues and making them
easier to examine and study. Leaving
specimens in the solution too long can cause the bodies to burst, however, so
watch them carefully. Small insects
should not remain in the solution for more than 30 minutes while larger ones,
such as a medium-sized caterpillar, might require 2 to 3 hours. After they are fixed
in the solution, they should be transferred to 70 percent alcohol in tightly
closed vials, with rubber stoppers.
Chemicals
can be purchased directly from biological supply houses. Also, grain (ethyl) alcohol is sold in liquor
stores in many states as “Everclear”, a
product that is 95% pure . Price will
vary depending on the level of state and federal taxes. Vodka is another option, but it is usually
sold at 40% strength. The 95% pure
alcohol, or ethanol can be easily diluted to 70% strength by working in units
to get the amount you need. To dilute
95% alcohol to 70%, use “about” (slightly less than/actually 2.8) 3 parts of
95% alcohol to 1 part distilled water.
Note that collection and specimen identification labels
must accompany insect specimens in each vial (labeling will be discussed in
detail later). With the insects in the
solution, top off the liquid to within 1/4" of the top of the vial. Wipe off the excess alcohol, then place an
insect pin against the interior of the vial, and push a rubber stopper deep
into the vial opening as the pin is simultaneously withdrawn. This procedure
“burps” the bottle, forcing surplus air out of the vial as a stream of tiny
bubbles, thus helping to ensure an airtight fit. Otherwise, the stopper may pop out --
especially if the stopper or inside vial rim were wetted by the alcohol. Because the body contents of a large specimen
may dilute the preservative, it is best to replace or top off the original
alcohol with fresh alcohol after a day or two.
After this special treatment, colors should not fade much. Over time,
the alcohol may evaporate, so it may be necessary to add a bit more from time
to time.
PINNING, MOUNTING AND DISPLAYING INSECTS
Temporary Storage Boxes
You will need a least one, but more likely two “Schmidt
Boxes”, a specially designed and constructed container for long term insect
storage. The lid is tightly fitted to
the box to help prevent entry of scavenger insects which feed on dead insect
specimens, into the box. Cigar boxes
make excellent containers for temporary storage of pinned insect
specimens. Line the bottom of cigar
boxes with styrofoam material, corkboard, balsa or cardboard to receive and
hold the insect pins. While cigar boxes are fine for temporary storage, they
are poor over long periods of time. For
extended storage and for display, tighter containers are essential. Add naphthalene crystals, placing them into a
small container in one corner of each display box to prevent damage to your
specimens.
Insect Pins
Special pins are needed to pin insects. They come in several sizes from 00 through 7,
the size of the pin increasing with each number. Number 3 insect pins are the best for most
purposes. Insect pins are purchased from
biological supply houses and can be found in some hobby stores. Never use common pins.
Pin Storage Rack
A 4-inch long section of 2" x 4" lumber with 6
one-half inch diameter drilled holes, each 3/4" deep, makes a handy pin
storage rack.
Pinning Block
Larger insects should be mounted using a wooden pinning
block, a simple piece of equipment. A
very small hole is bored almost through the bottom in the middle of each step.
A simpler pinning block can be made by drilling three holes—1, 3/4, and 1/2
inch deep—into a small wooden block. Proper use of a pinning block will result
in an attractive collection with the insect, collection and identification
labels in uniform position. Note the
dimensions of a pinning block in the drawing below.
Spreading Board
Mounting butterflies and moths is a special technique
that requires a spreading board to do an attractive job. The spreading board is
usually made of soft pine with a piece of balsa or cork underneath the center
groove to receive insect pins. An acceptable spreading board can be made from
balsa wood or cardboard strips, 2 heavy paper clasps, four corks and four
common pins. Spreading boards can also
be ordered from biological supply houses and hobby stores.
Pinning Insects
When working with your collection, be sure to follow
these instructions precisely and routinely.
Improperly pinned insects in your collection will be discounted. The rationale and main goal in developing and
using proper procedures in pinning insects is to effectively expose and display
critical details of insect structure -- the taxonomic characters which
are used by insect classification experts (taxonomists) to key and identify
insects.
The proper way to pin an insect depends on the type of
insect that you have collected. Remember that soft-bodied insects such as
caterpillars, mayflies, silverfish and some others cannot be pinned. The following diagram illustrates the proper
way to pin various orders of insects.
Note that the pin is usually just slightly to the right of the midline
of the insect. Specimens should also be level and squarely mounted on the pin
as shown. The use of a pinning block
will help in obtaining proper height and positioning.
First,
place the pin in the insect thorax in the proper position on the top step of
the pinning block, pushing it in so that the top of the insect is quite close
to the pin head. Then, remove the pin
from the top step, reverse it and place the head of the pin in the lowest step
of the pinning block. Push it down as
far as it will go. This will result in positioning each insect about one-fourth
inch from the pin head. The middle step
on the block is to position the collection label. The lowest step is used to position the
insect identification label.
Very small insects (less than 3/16 inch) should either be
pinned with minuten nadeln (German for “tiny needles”), or glued on
their right sides to tiny paper triangles. The latter procedure is called pointing. When pointing, first push a regular insect
pin (No. 2 or 3) through the butt end of the triangle. Level the triangle by pushing the pin through
the hole in the highest step of your pinning block. Bend the tip of the paper triangle slightly
downward with a forceps and touch it to a tiny drop of glue or clear fingernail
polish. Pick up the small insect
carefully with forceps and mount it by touching it on its thorax (right side)
to the drop of glue. Adjust the insect
so that it remains squarely in position, then allow the glue to dry.
When
using minuten, be very careful because they stick to the fingers and can
easily be transferred to the mouth, nose or eyes simply by rubbing. The figure below indicates how minuten
are used and the final position of the insect specimen.
Pinning and Spreading Butterflies and Moths
These insects must be done correctly or else their
appearance will detract from the overall quality of your collection. This is an area where many beginning
entomology students get off on the wrong foot, because they collect the
insects, but don’t get them pinned right away.
In some cases it may be necessary to store them temporarily until they
can be pinned.
Insects with large wings, such as butterflies, moths and
dragonflies, can be temporarily stored and dried in paper triangles until you
have time to relax, pin and spread them.
rite the collection data on the outside of the triangle so that you have
when you are ready to mount and label the specimen. Then place the freshly collected, pinched
and killed insect inside the triangle with the wings held together above the
body. Store them like files in an insect
storage box with a tight fitting lid and add naphthalene crystals if the
specimens will be stored for an extended period. Working with fresh specimens is much
easier. Before trying to pin them, the
specimens must be relaxed, as described earlier.
When pinning and spreading a butterfly or moth, before
you begin to work, cut several thin strips of paper about 1/4" wide and
8"-10" long. Once these are
ready, pick up the insect by the thorax and carefully push a pin through the
middle of the thorax. Adjust the
position of the butterfly on the pin and make sure that it is level, both on
the sides and in both front and back.
Place the pin into the hole in the tallest step of the pinning block,
being careful not to damage the fragile wings.
Adjust the width of the groove in the spreading board to be just
slightly wider than the body of the butterfly.
Remove the pinned insect from the pinning block and push the pin into
the slot of your spreading board until the bases of the wings are just level
with the top of the two side pieces. On
some spreading boards this may require the use of a pin pliers, a tool that
allows you to place pressure on the lower part of the pin, so that it will more
easily penetrate the cork or balsa wood strip.
With the fingers this is difficult or in some cases not possible.
Slip a paper strip between the wings (if they are
upright) and use it to force the wings on one side down into position. Pin the
ends of the paper down to hold the wings loosely in place. Do the same with the
wings on the other side, also pinning the ends of the paper down.
Now take another insect pin or needle and slip the point
through the leading edge of the right forewing (there is a strong vein just at
the front edge of each wing) near its attachment to the thorax. Be careful not
to tear the wing. Loosen the forward end of the paper strip and gradually bring
the forewing up into final position. Pin the wing down with a paper strip.
Repeat this procedure with the forewing on the other side. Using the same
technique bring both hindwings into proper position and fasten all four wings
firmly with the paper strips.
Note carefully that the rear edge of the two forewings
should make a perfectly straight line across the back. The hindwings should
be pinned so that the rear edge is held just slightly away from the abdomen.
Position antennae with pins and if the abdomen has drooped, prop it up with
pins so that it dries in a natural position.
Allow specimens to dry for several days before you remove
the pins. Drying “freezes” the wing muscles of the insect in position. Rushing the drying process somewhat by
placing specimens in an oven at 125EF. for about an hour will work, but may result in the
wingtips curling upward and spoiling the insect's appearance. Be very careful if you attempt this. Using wider (3/4 inch) paper strips to hold
the wings down will help to prevent distortion.
Please see the illustrations below and movie clips for further detail on
pinning lepidopterans.
Large-bodied moths like Cecropia should be cut
open on the underside of the abdomen and the contents removed with a cotton
swab. The body cavity should be filled with cotton so that the specimen looks
natural from above. If this is not done, the fatty material in the abdomen will
decompose, releasing oils which may discolor and ruin the specimen.
Labeling Insects
A collection has little value unless each insect is
properly and accurately labeled. Labeling must be done as soon as possible
after collecting, pinning and mounting or vital information may be lost. Note that many insects in museums today stand
as living documents of biological diversity.
Their precise collection locations, habitats, and data on plants on
which they were found is important documentation. Many of these habitats have been or are being
altered and in some cases destroyed.
Many plant and animal species, once common and together in biological
ecosystems, are now endangered or in some cases are already gone. It is essential that the presence of insects,
plants and other creatures be documented for future generations.
Make your labels with your computer and print them
off. Trim labels with a sharp paper
cutter so the edges make nice, clean, and flat rectangles. Two labels should be placed on the pin below
each insect specimen. Both labels should
be of the same size and lined up parallel to the length of the body of the
insect (not cross-wise). The insect
head should be at the left and the label should read from left to right. However, in the case of "pointed" specimens, the labels
should be parallel to the length of the point.
The top label should have the county and state in which the insect was
collected, the collection date and the name of the collector. The lower label
should show the Order name of the insect. Many entomologists place another
label beneath the collection label which gives the host plant, habitat or other
pertinent information, however, this label is not required for ENT116. Print
the information on the labels as neatly as you can. Neatness, accuracy and
quality are important.
Insect Label Data
Collection (First) Label:
Locality:
Lincoln, NE
Date: 09/26/03
Collector:
D. L. Keith, Coll.
The above label was reduced
(below) to a font size of 6.
Lincoln, NE
09/26/03
D.
L. Keith, Coll.
Second Label:
Order Name:
Orthoptera
Family Name: Acrididae (10 specimens identified to
family)
Organizing Your Insect Collection in Schmidt Boxes
Do not pin vials of insects in Schmidt boxes! These often come loose, roll around and
damage insect specimens. Keep your vials
in a plastic bag with some tissue or styrofoam “popcorn” to cushion them and
prevent breakage. Otherwise, use strong
rubber bands to hold vials together.
Place only neatly pinned and labeled specimens in collection boxes. Organize them into sections by taxonomic
grouping (i.e. Order) and position and space all labels neatly on the pin, so
that the specimens are arranged in neat rows.
Place a large label below and in the center of each order group. Order labels should be about 2" long,
1/2" wide and neatly printed with black lettering. Neatness in pinning, mounting and displaying
insects is important.
