Collecting
can be as simple as picking up stray ants and placing them in a glass jar or as
complicated as completing an exhaustive survey of all species present in an area
and estimating their relative abundances. The methods used will depend on the
final purpose of the collections. For taxonomic studies, long series from a single
nest which contain all castes (workers, including majors and minors, and if present,
queens and males) is desirable to allow the determination of variation within
species. For ecological studies, the most important factor is collecting identifiable
samples of as many of the different species present as possible. Unfortunately,
these methods are not always compatible, with the taxonomist sometimes overlooking
species in favour of those groups currently under study and while the ecologist
often collects only a limited number of specimens of each species, thus reducing
their value for taxonomic investigations.
To collect as wide a range of species as possible, several methods must be used.
These include hand collecting, using baits as attractants, ground litter sampling,
and the use of pitfall traps. For a general overview of collecting methods, see
Upton (1992).
Hand collecting consists of searching for ants everywhere they are likely to occur.
This includes on the ground, under rocks, logs or other objects on the ground,
in rotten wood on the ground or on trees, in vegetation, on tree trunks and under
bark. When possible, collections should be made from nests or foraging columns
and at least 20 to 25 individuals collected. This will assure that all individuals
are of the same species and
increase their value in detailed studies. Since some species are largely nocturnal
collecting should be done at night as well as during the day. Specimens are collected
using an aspirator (often called a pooter), forceps or a fine, moistened paint
brush, or with fingers if the ants are known not to sting (unless, of course,
the collector enjoys pain). Individuals are placed in plastic or glass tubes (1.5
- 3.0 ml capacity for small ants, 5 - 8 ml for larger ants) containing 75% to
95% ethanol. Plastic tubes with secure tops are better than glass because they
are lighter and do not break as easily if mishandled.
Baits can be used to attract and concentrate foragers. This often increases the number
of individuals collected and will sometimes attract species that would be difficult
to locate otherwise. Sugars and meats or oils will attract different species and
both should be utilised. Honey is a good sugar source while tuna or cat food are
readily available and inexpensive meat sources. These baits can be placed either
on the ground or on the trunks of trees or large shrubs. When placed on the ground
baits should be situated on small paper cards or other flat, light-coloured surfaces,
or in test tubes or vials. This makes it easier to spot ants and to capture them
before they can escape into the surrounding leaf litter.
Many ants are small and forage primarily in the layer of leaves and other debris on
the ground. Hand collecting these species can be difficult. One of the most successful
ways to locate these small, cryptic foragers is to collect the leaf litter in
which they are foraging and extract the ants from it. This is most commonly done
by placing leaf litter on a screen above a large funnel, often with a heat source
above the leaf litter (a Berlese funnel). As the leaf litter dries from above,
ants (and other animals) move downward and eventually fall out the bottom and
are collected in alcohol placed below the funnel. This method works especially
well in rain forests and wet sclerophyll areas. A method to improve the catch
when using a funnel is to sift the leaf litter through a coarse screen before
placing it above the funnel. This will concentrate the litter and remove larger
leaves and twigs. It will also allow more litter to be sampled when using a limited
number of funnels.
The pitfall trap is another commonly used tool for collecting ants. A pitfall trap
can be any small container placed in the ground with the top level with the surrounding
surface and filled with a preservative. Ants are collected when they fall into
the trap while foraging. The diameter of the traps can vary from about 18 mm to
10 cm and the number used can vary from a few to several hundred. The size of
the traps used is influenced largely by personal preference (although larger sizes
are generally better) while the number will be determined by the study being undertaken.
The preservative used is usually ethylene glycol or propylene glycol, as alcohol
will evaporate quickly and the traps will dry out. If specimens will not be needed
for long-term storage, automobile anti-freeze can be used successfully, although
the dyes used may discolour some specimens. One advantage of pitfall traps is
that they can be used to collect over a period of time with minimal maintenance
and effort. One disadvantage is that some species are not collected as they either
avoid the traps or do not commonly encounter them while foraging. For further
discussion on the use of pitfall traps, especially in ecological studies, see
Greenslade (1973), Andersen (1991), Abensperg-Traun and Stevens (1995) and Borgelt
and New (2005, 2006).
When possible, members of a single nest or foraging column should be kept together.
This will assist later when determining the amount of variation within a species
and helps associate workers with queens and males (when present). Similarly, pitfall
or bulk-collected material should be labelled so that extra care can be taken
to determine if several similar species are present or if there is only a single,
variable species. One commonly used method to associate members of a single collection
is to assign it a sequential number. Using this system is helpful because it reduces
the time needed to label individual tubes in the field, can be used to cross reference
field notes with specimens, provides information on which individuals are from
the same nest or foraging column, and can be used to associate specimens stored
on pins and in alcohol (see
Specimen Preparation).