When you are wandering through woods or fields, do you realize that you
are stepping on more insects than you ever see? The ground cover and
soil are inhabited by a vast assemblage of little animals that are
seldom seen by the casual collector. Because many of these animals are
exceedingly minute, they are difficult to see and collect by ordinary
methods.
Construction.--The most efficient method for collecting this fauna is by
the use of Berlese funnels, named after the Italian entomologist Berlese
(pronounced Bur-lazy), who first used them extensively. A Berlese funnel
is a very simple apparatus, consisting of a fairly long funnel,
suspended wide end up, with, a screen placed about a third of the way
down the funnel; heat is applied either around the upper portion or over
the top of the funnel, and a container of preservative, preferably 80
per cent ethyl alcohol, is placed at the small bottom opening. Leaf mold
or other material is placed on the screen, the heat source is turned on,
and soon the animals begin to leave the drying sample and migrate
downward, dropping into the preservative.
[Illustration: Fig. 7.--Diagrammatic cross section of a Berlese
funnel. The central figure shows an arrangement for a steam coil,
the lower left for an electric light.]
Fig. 7 illustrates a funnel that has proved very satisfactory; it is 15
inches from top to bottom, and the top has a diameter of 12 inches. The
bottom opening, seven-eighths inch in diameter, fits into the mouth of
the bottle containing the preservative. Three angled brackets or hangers
are soldered inside the funnel to provide a rest for the screen, which
is made of quarter-inch or eighth-inch mesh hardware cloth; the mesh
used depends upon the type of sample. A battery of several funnels in a
rack, fig. 8, will allow the collector to sample several kinds of
material at the same time.
If steam is used as a source of heat, the small copper lines that
conduct it act as a partial support for the funnel by encircling it
about halfway between the screen and the top; a piece of cloth is tied
tightly over the top of the funnel to prevent the upward escape of
animals. If an electric light is used for heating, it should be hung
directly over the center of the funnel, no cloth should be tied over the
top, and the light should have a reflector nearly as wide as the top of
the funnel.
[Illustration: Fig. 8.--Berlese funnel in position on rack. Each
funnel rests inside a double ring of copper tubing (visible at
extreme lower left), through which live steam flows. The steam
produces heat that dries out the sample of leaf mold in the funnel
and drives animals into a bottle of preservative below. Cotton or a
small rag is tamped between the end of the funnel and the mouth of
the bottle to prevent escape of specimens.]
Care must be taken not to heat the sample too rapidly. Otherwise, either
moisture will condense in the lower part of the funnel and trap many of
the animals working their way toward the bottom, or the heat will kill
many of the organisms before they have an opportunity to move out of the
sample. An application of heat sufficient to dry the sample in 4 or 5
days is usually satisfactory.
The Berlese funnel is extremely useful for collecting many groups of
beetles (particularly Staphylinidae), thrips, springtails, many groups
of parasitic Hymenoptera, ants, mites, pseudoscorpions, millipedes,
centipedes, and a wide range of other minute animals that live in soil,
surface cover, logs, or bark.
Collecting Berlese Samples.--Many different habitats and micro-habitats
provide good samples for the Berlese funnel. You will find that, for
general collecting, various types of ground cover are excellent; for
leaf mold samples, scrape off and discard the dry surface leaves and
scoop up the lower, rotted layers of leaves together with an inch or two
of the adjacent soil. You may encounter especially good samples where
leaves have blown in along the edge of a log. In such a situation, take
some of the log bark with the sample. Collect rotten log samples in
large hunks and break them up just before putting them in the funnel.
From either standing stumps or fallen logs in which the wood is still
too hard to break up, collect the loose bark, as it is often quite
productive. Frequently, if you roll a log over, you may find animal runs
under it; the debris and earth under and around these runs, together
with animal nests, frequently give unusual catches, such as larvae and
adults of fleas and rare ticks. Especially productive are samples taken
from the interior of a standing hollow tree; from the bottom of the
hollow you can scoop out a foot or more of fine, rotten, woody material
rich in rare insects.
Certain items placed in the funnel may produce distinctive and unusual
catches. Recently deserted birds' nests will give mites and, frequently,
rare beetles, flies, and their larvae; mature or overmature mushrooms
and bracket fungi are often rich in beetles, thrips, and maggots; bark
of living trees may produce unusual thrips, springtails, and psocids;
debris from aquatic habitats and from the wet edges of ponds and tiny
streams may be productive of rare aquatic and semiaquatic forms. Moss is
a good source of peculiar species of springtails, thrips, and beetles;
the moss should be rolled up carefully while being transported.
Handling Berlese Collections.--In the field, put samples of leaf mold or
other material in tightly woven cloth bags or strong paper bags for
transportation. It is convenient to have small paper bags for mushrooms,
nests, and other small items, and larger bags for ground cover, moss,
and the like. When collecting ground cover and similar material, put in
each bag enough of a sample so that it will not shake around loosely,
but do not pack it tightly. Be sure that samples do not overheat while
being transported.
Samples may be collected at any season. If collected during warm
weather, they should be taken to a laboratory and placed in the funnels
within a day or two; otherwise, considerable loss of population occurs
within the samples. If collected during cold weather, they may be kept
in cold storage for a week or two with little loss of fauna.
In putting material in the funnel, lay it carefully on the screen to a
depth of a few inches. Moss and sod should be placed upside down in a
single layer on the screen. In the case of dense material, pile the
sample chiefly around the sides of the funnel and leave an opening in
the middle, as shown in fig. 7. After the funnel is loaded, place it in
the rack, put the bottle of preservative under it, and apply the heat.
By substituting a different kind of collecting bottle at the bottom of
the funnel, you may obtain live material for rearing. The exact changes
necessary to obtain live material will depend upon your ingenuity and
the type of material you desire.