Insects have extraordinary species richness: over a million species have been identified, and even more await discovery and classification. Given their abundance and diversity, insects are excellent teaching tools for science classrooms. However, accurate insect identification can be especially challenging for beginning students. Accordingly, we have developed a dichotomous key that both precollege and university instructors and students can use efficiently to correctly identify 18 taxonomic orders of insects. Our key was developed to target insects most commonly encountered throughout the coastal southeastern United States, but it can easily be adapted to other regions. This key is novel in that it incorporates not only adult insects but also their immature stages. In addition, we included insects that are likely to be collected in all seasons, facilitating implementation in the classroom throughout the academic year.
Educators and students recognize that insects are ubiquitous animals that are ecologically essential as well as medically and economically important. At the K–16 level, insects are an excellent model organism to introduce students to biological conservation (Kishbaugh & Yocom, 2000; Snaddon et al., 2008), microscope use (Potter et al., 2001), biodiversity analyses (Richardson & Hali, 2008; Lampert & Morgan, 2015), forensic science (Carloye, 2003), and molecular techniques (Bordenstein et al., 2010). For educators, insects serve as a valuable tool because they are readily available and are not subject to the strict animal-use regulations associated with vertebrates. Yet, for non-entomologists, identification of insects can be a daunting task because of their staggering diversity and diminutive size.
There are millions of insect species that belong to at least 30 different orders (i.e., the rank below class and above family), making them the most abundant and species-rich animal group. The common names of many insect groups are associated with the name of the group's order: for example, flies are Diptera, beetles are Coleoptera, and earwigs are Dermaptera. Field guides and identification keys are readily available in print and online but require the user to be well versed in insect morphology. In addition, many keys are restricted to adult insect specimens (e.g., Borror & White, 1970). For a non-entomologist, distinguishing adult from immature specimens can be difficult. Adult insects are defined as individuals that have completed their last molt, are sexually mature, and have fully developed wings. This determination can be straightforward for butterfly or bee specimens but a challenge for insects that have incomplete (gradual) metamorphoses. For example, the wings of immature cockroaches may appear to be absent in young stages but will gradually increase in size after each molt. Finally, adult insects are readily available in summer and early fall months but can be difficult to collect in colder months. More easily recognized adult insects such as butterflies, dragonflies, and flies are rarely collected in winter. Thus, there is a need for a simple insect identification key that can be used by novice collectors during any season.
Students may be quick to observe a specimen, without closely studying it, and presume its identity on the basis of their limited experience. Identifications based on matching images obtained from the Internet or field guides can also be problematic. Pictorial keys (Milne et al., 1980; Eaton & Kaufman, 2007) are commonly used but rely on the ability of the user to match adult insects by general form or gestalt. Without careful examination of an insect, students run the risk of misidentifying their specimens, especially those that are mimics. Figure 1 clearly illustrates an example of the dilemma posed by mimics when a single image is used for the purpose of identification. Which specimen is the bee (order: Hymenoptera) and which is the fly (order: Diptera)?
In fall 2013, the Biology Department at Armstrong State University redesigned its first-semester introductory biology laboratory course (Principles of Biology I) to launch a new research-based curriculum that is adapted from the national “Discover the Microbes Within! The Wolbachia Project” (see http://discover.mbl.edu/). As a first step in the project, students collected insects from sites around campus and were given the task of identifying their specimens using an online tool employed in the original Wolbachia project (Bordenstein et al., 2010). Like similar classes at other universities, our introductory lab course has a high enrollment (up to 26 sections of 24 students each semester) and is taught by a staff of part-time and full-time instructors with a diverse array of educational training, most without any entomological experience. Even with appropriate training, an instructor must review enough background and insect morphology in class for introductory students to effectively implement existing keys. This may require more time than is available for lab exercises designed to be completed in one session.
Anecdotal evidence suggested that both students and instructors in our course were having problems with the identification process when the previously mentioned online key was used. This prompted us to have an entomologist review the accuracy of a subset of the insect identifications from students' end-of-semester PowerPoint presentations. Out of 69 insects reviewed from fall 2013, seven (10.1% error rate) had been misidentified (see Figure 2). Some of these insects had been erroneously classified as uncommonly encountered or rare orders, such as Strepsiptera, Thysanoptera, and Embioptera.
Stagg et al. (2014) showed that undergraduate students performed better when using a printed dichotomous key, as compared with a web-based key, when trying to identify nonvascular plants. To simplify the identification process and decrease the overall error rate, we designed a dichotomous key that was integrated into our introductory course beginning in spring 2014. When using the key, students made a choice between paired couplets based on the physical characteristics of their insects, which were observed by eye or with a dissecting microscope. Students were required to document the features that contributed to the identification process for inclusion in a post-lab assignment and in their final presentation. Photographs were discouraged, and instructors emphasized to students the importance of drawing and labeling the details of their insects (see Dempsey & Betz, 2001; Landin, 2015). Students made careful observations of features they had previously paid only cursory notice. Subsequent analyses of students' identification slides (represented in Figure 3) determined that these instructions and use of the simplified key resulted in a 2.3% error rate (two misidentifications out of 88 identifications reviewed), a significant improvement when compared to that in the previous semester (Fisher's exact test, P = 0.0434).
Here, we present a dichotomous key with a brief tutorial exercise that can be used by students and educators who have little background in entomology. This key was specifically developed for insects found in coastal Georgia, but its use is not restricted to that region. This key is also unique in that it includes adult and immature specimens that can be found in terrestrial, aquatic, and subterranean (i.e., under logs and in the soil) environments, which are more protected from freezing temperatures. Therefore, this key can be used in classes that are offered year round.
Use of this dichotomous key requires that students make detailed observations and drawings of the insects they collect. After completing this activity, students will
Describe the ubiquity of insects and explain how their abundance is reflected by their morphological diversity
Demonstrate how to properly use a dissecting microscope
Draw and correctly label an insect specimen
Demonstrate how to use a dichotomous key to identify the taxonomic order of an insect
Prelaboratory Exercise for Students
Students review a short reading assignment and a PowerPoint presentation that provide background information about insects and their basic morphology. This information includes the fact that insects comprise a single class, albeit the largest, within the phylum Arthropoda. All insects have one pair of antennae, six legs, and three body regions (head, thorax, and abdomen). They are the only arthropods to have wings, but the number can vary (two or four) or be absent entirely. Only adult insects will possess fully developed wings: for example, butterflies have wings, but their larvae (caterpillars) lack them, and the wings of immature grasshoppers are reduced compared with those of an adult.
Students are given the following three questions to prepare them to use the dichotomous key in class. For this exercise, we recommend using images of actual specimens rather than stylized line drawings.
Identify and label each of the following parts of the insect in Figure 4:
Careful identification of mouthparts is essential for accurate classification. Some insects have specialized mandibles for chewing and shredding solid food, whereas others have long, tongue-like mouthparts for taking in liquids. Most insects also have finger-like accessory mouthparts (labial and maxillary palps) for food handling and tasting. If possible, the head of the insect can be separated from the rest of the body for better inspection of mouthparts and other appendages.
Look carefully at the head of the insect shown in Figure 5 and identify each of the following parts:
labial/maxillary palps (accessory mouthparts)
The mouthparts are indicated with an arrow in each of the following images (Figure 6). Next to the arrow, write your prediction of the diet (solid or liquid) of each insect based on the morphology of its mouthparts. Keep in mind that mouthparts can often be tucked far under the head.
Drawing & Examining Insects
Instructions provided to students:
Use a dissecting microscope to view the basic morphology of your specimen. Spend at least 30 minutes carefully drawing a top-and-bottom view of your insect, highlighting its distinguishing features.
Find the wings on your specimen. Insect wings and legs are located on the thorax of insects. While legs are ventrally (Latin venter; “belly”) located, wings are on the dorsal (Latin dorsum; “back”) surface. Wing texture can be transparent and membranous, leathery, or shield-like and rigid. In many insects, the forewings might completely cover and conceal the hindwings. In other insects, such as bees and wasps, the two pairs of wings are joined together by small hooks, giving the illusion that only one pair of wings is present. When looking at an insect, tease the wings apart with a pin or tweezers to see if a second set of wings is absent or just concealed.
Use the following dichotomous key to identify your specimen. A dichotomous key is a common tool used in biology to identify organisms. As the user moves through each step (couplet), the identification of the organism is gradually narrowed down. Start at number 1 and move through each couplet as instructed throughout the key. The numbers in parentheses indicate the previous couplet used and can enable students to work backward in the key if a mistake is made. Keep in mind that although this key covers the majority of insect groups, it is not fully comprehensive.
|1.||Insect has fully developed wings……go to 2|
|1'.||Insect has reduced wings or no wings. If underdeveloped wings are present, they do not extend past the tip of the abdomen……go to 16|
|2(1).||One pair of well-developed wings (hindwings are reduced to tiny knobs located immediately behind the forewings)……Diptera (flies)|
|2'.||Two pairs of well-developed wings……go to 3|
|3(2).||Mouthparts are absent or much reduced and not functional, although accessory mouthparts (labial and maxillary palps) are often well developed……go to 4|
|3'||Mouthparts are visible and appear to be functional……go to 5|
|4(3).||Fine hairs cover the wings, which are held like a tent over the body……Trichoptera (caddisflies)|
|4'.||Bare wings are held flat against the abdomen……Plecoptera (stoneflies)|
|5(3).||Mouthparts are beak-like or tube-like for piercing, sucking, or siphoning liquids, but mandibles for chewing solids are absent……go to 6|
|5'.||Mouthparts with mandibles for chewing……go to 7|
|6(5).||Tube-like mouthparts are usually long and coiled. Wings are covered in microscopic overlapping scales that are powder-like……Lepidoptera (moths and butterflies)|
|6'.||Mouthparts are straight and beak-like, needle-like, or syringe-like. Wings lack scales……Hemiptera (true bugs)|
|7(5).||Forewings and hindwings have different textures. Forewings are rigid, thickened, leathery, or thin like parchment paper. Hindwings are transparent like cellophane……go to 8|
|7'.||Both forewings and hindwings are transparent like cellophane, though they can be clear or tinted……go to 12|
|8(7).||Terminal appendages on tip of abdomen form large pincers (see Figure 8C)……Dermaptera (earwigs)|
|8'.||Tip of abdomen lacks obvious pincers……go to 9|
|9(8).||Forewings are shield-like, lack visible veins, and form a straight line where they meet dorsally……Coleoptera (beetles)|
|9'.||Forewings are thick and leathery, and veins are visible……go to 10|
|10(9).||Body is flattened and head is mostly concealed from above by thorax (see Figure 8D)……Blattodea (cockroaches)|
|10'.||Body is not flattened and head is visible from above……go to 11|
|11(10).||Front legs are armed with spines and modified for prey capture……Mantodea (mantids)|
|11'.||Front legs are simple, but hind legs are enlarged and modified for jumping……Orthoptera (grasshoppers, katydids, and crickets)|
|12(7).||Wings with many crossing veins that form tiny cells throughout the wing (see Figure 7B)……go to 13|
|12'.||Wings with simple veins that occasionally cross to form just a few closed cells throughout wing (see Figure 7A)……go to 15|
|13(12).||Front wings are large and triangular, and hindwings are small and rounded. Tip of abdomen has two or three long whip-like filaments (see Figure 8B)……Ephemeroptera (mayflies)|
|13'.||Wings are similar in shape and size. Abdomen lacks long filaments……go to 14|
|14(13).||Antennae are reduced to tiny bristles……Odonata (dragonflies and damselflies)|
|14'.||Antennae are long and well developed……Neuroptera (lacewings and antlions)|
|15(12).||Front wings are usually larger than hindwings and may be connected by tiny hooks. A thin waist often separates the thorax from the abdomen. Eyes are large and are the prominent feature of the head……Hymenoptera (bees, wasps, ants, etc.)|
|15'.||Wings are similar in size and shape but are held flat and overlap the abdomen when at rest. There is no waist, and eyes are small……Isoptera* (termites)|
|16(1).||Segmented body lacks jointed legs (fleshy bumps and hairs may be present)……go to 17|
|16'.||Segmented body has 3 pairs of jointed legs on the thorax……go to 18|
|17(16).||Head is well developed, with visible mouthparts……Coleoptera (grubs)|
|17'.||Head is not well developed, and it is often hard to tell which end is which……Diptera (maggots)|
|18(16).||In addition to the jointed thoracic legs, specimen has several pairs of fleshy abdominal appendages……go to 19|
|18'.||Has jointed thoracic legs only. If other appendages (tails or pincers) are present, they are restricted to the very tip of the abdomen……go to 20|
|19(18).||Has up to five pairs of fleshy abdominal legs with microscopic hooks (crochets) at the tips for grasping leaves or branches……Lepidoptera (caterpillars)|
|19'.||Has more than five pairs of fleshy abdominal legs and lacks crochets……Hymenoptera (sawflies)|
|20(18).||Is aquatic, and mouthparts are modified into a long, hinged “mask” with toothed mandibles. When extended, the mouthparts can double the length of the head……go to 21|
|20'.||Is aquatic or terrestrial, and mouthparts are not as described above……go to 22|
|21(20).||Has three well-developed, long abdominal appendages (feathery or filamentous) that are 1/4 to 1/2 the length of the abdomen……Odonata (damselfly nymph)|
|21'.||Lacks abdominal appendages or, if present, they are much shorter than described above……Odonata (dragonfly nymph)|
|22(20).||Hind legs are large and modified for jumping……Orthoptera (grasshoppers, crickets, and katydids)|
|22'.||Hind legs are of similar size to the other two pairs and are not enlarged for jumping ……go to 23|
|23(22).||Abdomen with leg-like tails or pincers (see Figure 8A–D)……go to 24|
|23'.||Lacks obvious abdominal appendages or, if present, they are much reduced (and not as seen in Figure 8A–D)……go to 27|
|24(23).||Abdomen ending in large pincers (see Figure 8C)……Dermaptera (earwigs)|
|24'.||Abdomen with long hair-like or short leg-like appendages……go to 25|
|25(24).||Three long abdominal tails and body covered in microscopic, silvery scales. Common house pest (see Figure 8A)……Thysanura (silverfish)|
|25'.||Two short abdominal appendages……go to 26|
|26(25).||Abdominal appendage is often forked and tucked under the body. Head is easily visible. Common soil inhabitant that is often so small that it is barely visible with the naked eye……Collembola* (springtails)|
|26'.||Abdominal appendages are not forked. Body is flattened and head is mostly concealed from above by thorax (see Figure 8D)……Blattodea (cockroaches)|
|27(23).||Mouthparts are beak-like or tube-like for piercing, sucking, or siphoning liquids, but mandibles for chewing solids are absent……go to 28|
|27'.||Mouthparts have mandibles for chewing……go to 29|
|28(27).||Commonly a parasite of dogs and cats. Body is flattened laterally (compressed on sides)……Siphonaptera (fleas)|
|28'.||Not typically a parasite found on animals. If body is flat, it is flattened dorsoventrally (compressed top to bottom). ……Hemiptera (bugs)|
|29(27).||Has long antennae…….go to 30|
|29'.||Antennae are highly reduced. Often are active and colorful or have white and gray C-shaped bodies……Coleoptera (grubs)|
|30(29).||Antennae are long but are strongly bent or “elbowed” in the middle. Color is often black or red……Hymenoptera (ants)|
|30'.||Antennae resemble straight chains of beads. Body is white and ant-like……Isoptera* (termites)|
* The classifications of the orders Isoptera and Collembola are currently undergoing revision (on the basis of molecular evidence), but the common names “termites” and “springtails,” respectively, should remain unchanged.
Because insects are the most diverse group of animals, their identification can be challenging to inexperienced investigators. Current guides and keys have limited overall use because they often rely on sophisticated terminology or focus only on adult insects. We have developed a simplified taxonomic key that can be used by novices to identify mature and immature insects to the level of order. In fact, implementation of this key in an introductory biology lab resulted in a significant decrease in student misidentifications of their insects when compared to the use of a free online key. Our key is based on morphological traits (e.g., sucking vs. chewing mouthparts, wing number, and wing development) that students, instructors, or enthusiasts can readily characterize using a dissecting microscope. Embedded in the key are example images to illustrate the few traits that are more challenging for a novice to ascertain, such as wing venation patterns. Although the insect key is not comprehensive, it covers those orders most commonly encountered in the southeastern United States, and it can be used for most other regions in North America. It does not include all insect groups (i.e., immature stages of insects that are mostly associated with lotic environments such as mountain creeks or rivers), but this key can easily be adapted to include couplets for specific groups of insects that are more regionally common. This key does incorporate insects that are frequently encountered in retention ponds around campuses and schoolyards. Coupled with the basic tutorial provided in the prelab assignment, this key is an educational tool that is adaptable for introductory college courses and K–12 schools. In a survey of seventh-grade life-science educators in Georgia, <5% of instructors had formal training in university-level entomology coursework (cited in Matthews et al., 1997). Thus, the simplicity of the key and the prelab tutorial allow both students and instructors without any formal training to successfully identify insects. When given ahead of time, the prelab reading and assignment can enable beginning students to come to class prepared to identify their specimens after a brief lecture and discussion. For younger K–8 students, the prelab reading and assignment could be adapted easily into an in-class lecture and discussion. Because many insects are challenging to identify, it is a good idea to encourage students to use the Internet, field guides, or consultation with a professional to confirm the identifications that they make using the key. Most significantly, students will make important observations of insect morphology while using the key and, in doing so, will learn about the features of insects that make them the most diverse and abundant group of animals. If the question is “To key or not to key,” we think the answer is a resounding “To key!”
Support for this work was provided in part by the National Science Foundation's TUES Program (award no. DUE-1245077). Additional support was provided by the Biology Department, the College of Science and Technology, and Armstrong State University. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation, the Department of Biology, the College of Science and Technology, and Armstrong State University. We thank Bil Leidersdorf for providing the photographs in the figures, and our introductory biology laboratory students and instructors for their valuable feedback. We also thank Drs. Robert Woodruff (Emeritus Taxonomist, Florida State Collection of Arthropods) and Ian Stocks (Entomologist, Division of Plant Industry, Florida Department of Agriculture and Consumer Services) for their helpful review of the dichotomous key.