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different natural histories and species names are used for filing and retrieving biological 
information (Gotelli, 2004). Because the specimens encountered in ecosystems do not 
come with species name tags, biologists have to use a variety of techniques for, a) 
delimiting (grouping specimens into species) (Wheeler & Meier, 2000), b) describing 
species (Winston, 1999), and c) identifying species (Walter & Winterton, 2007). 
Not surprisingly, the best techniques for these purposes vary from taxon to taxon. In 
addition, the best methods for species identification change over time. 
From an identification point of view, the most convenient taxa are those wherein 
species diversity is well understood (i.e., species delimitation and description are quite 
complete: birds, butterflies), species identification can be accomplished based on 
readily-accessible features (e.g. morphology, songs, etc.), and the relevant features 
for identification can be obtained without collecting or even disturbing the animals 
or plants. Fortunately, many vertebrate species fall into this category. On the other 
end of the scale are taxa where many/most species are neither delimited or described, 
and therefore not identifiable. Unfortunately, more than 90% of the world’s species 
(mostly invertebrates) fall into this category (Meier & Dikow, 2004; Odegaard, 2000). 
Intermediate along the spectrum of identification feasibility are taxa for which most 
species have been delimited and described by scientists, but identification is difficult for 
a variety of reasons. These include the lack of good identification tools (e.g. keys), the 
reliance on identification features that can only be used by a few taxonomic experts, and 
the use of identification features that are only visible during certain times of a species’ 
life cycle. Good examples are many insect species that can only be identified based on 
minute details of genitalia (Ang & Meier, 2010; Pont & Meier, 2002), species of plants 
that can only be identified when they happen to flower, and insects whose aquatic 
larval or nymphal stages are unidentifiable because identification tools only exist for 
adults (e.g. dragonflies, midges; Cranston et al., 2013). It is often the unidentifiable 
stages that are the most important, from an ecological and biomonitoring point of view 
(vegetative parts of plants, larval stages of insects). 
Identifying most species is a task that can currently only be performed by 
experts with extensive training in biology. Indeed, for many invertebrate groups 
there are only a handful of experts worldwide who can identify species (Gotelli, 
2004). This unfortunately means that many identification needs of society are not 
met. An alternative way of identifying species is through the use of so-called “DNA 
barcodes” (Hebert et al., 2003a; Meier et al., 2006, 2016; Meier, 2008). For animals, 
most biologists use a small piece of the cytochrome oxidase subunit 1 (COT) gene 
for species identification (“DNA barcode”; Hebert et al., 2003b). This particular gene 
sequence (barcode) is distinctly different between most species (Kwong et al., 2012a; 
Hajibabaei et al., 2007; Meier, 2008; but see Kwong et al., 2012b and Meier et al., 
2006). One advantage of using DNA barcodes is that it “democratises” the process of 
species identification. Instead of only having a handful of experts worldwide who can 
identify species in a particular group, DNA barcodes can be generated by thousands 
of laboratories around the world. In addition, the cost of obtaining DNA barcodes 
has been dropping rapidly so that the number of biologists with access to these kinds 
of data is also increasing rapidly (Wong et al., 2014; Meier et al., 2016). Barcoding 
