Teacher Field Activity Supplement and Insect Fact Sheet for Aquatic Insects Found in Mountain Streams and Their Adaptations How to use a kick net Place the net downstream from your sample area (so that the specimens get washed into the net by the flow of water), disturb the substrate, turning over rocks and sediment, and take what you have collected to the white pan with stream water in it. The white background makes it easier to see the insects and the water encourages them to move. There is a kicknet in the SC LIFE Natural History Equipment Footlocker. You can also purchase your own kicknet from Carolina Biological for $29.15, I recommend the one with the guard on it as it helps keep the net from tearing. A white sampling pan also comes in the SC LIFE Natural History Equipment Footlocker. Or you can purchase your own from any photography store that carries developing trays. They come in a variety of sizes and prices. How to use a sieve - Use it only in sandy depositional areas such as pools. Scoop the top 2 inches of substrate into the sieve, then shake it in the water to remove all the sand, leaving the critters behind. Use a standard sieve size 5 or 10, meaning it has openings of 4mm and 2mm respectively. The cheapest sieves I found were plastic, sold in a set of 4 different sizes, and could be ordered from Bioquip. They sold for $58.45 and contain sieve sizes 5, 10, 60 and 230. You can also use a colander, but they probably won't last as long. Do not cast aside the rocks so easily Aquatic insects like to cling to objects (CLINGERS!) so be sure to inspect the rocks in the sample area, putting them back when you are done. Fill a white pan with water - Take what you collected either in the sieve of the kick net, dump it into a pan with stream water in it, and wait for a few minutes, keeping the pan still. The insects will begin to move around and you will be able to collect them easier. Also note the way they move, you can see several adaptations up close by doing this. Be careful of the jaws! Some of these aquatic insects have hefty jaws and they have no problem with biting, so be careful. Use forceps if possible, but be careful not to mangle the insect when you do. I recommend Bioquip's featherweight forceps as they are field and student proof. The SC LIFE Natural History Equipment Footlocker has 2 pair of these forceps in them; however, if you want to purchase your own from Bioquip, they are $4.40 a piece. Keeping the insects alive If you want to bring some aquatic insects back alive, collect water from the stream in a clean jar, place the specimens in it, transport it in a cooler. You can keep the sample in the fridge (not the freezer!) overnight, but I wouldn't recommend much longer than that. Preserving the insects In the short term, you can preserve the insects in rubbing alcohol. In the long term, use 70% ethyl alcohol (EtOH). 1
Collecting the abiotic data Instructions for using the ph, temperature, dissolved oxygen and turbidity tests are in the kit (in the SC LIFE Natural History Equipment Footlocker). Or purchase water quality kits available from several sources, although I recommend using the LaMotte Green test kits. To get the overall stream flow, you can use a timer, a nerf ball or orange, and a tape measure, however, this does not work for flow in the small microhabitats. When using the flow meter, do not forget to use the mathematical formula to get the flow rate. The number on the meter only gives the number of revolutions the propeller makes. Plural vs. Singular - Larvae is plural, larva is singular. Insect legs - Insect legs are only attached to the thorax (wings, if present, are also only attached to the thorax). If there are any leglike appendages located anywhere else on the body, these are not true legs. Slide Show Notes Slide 31 - larval salamanders have gills, the red arrow in the presentation is pointing to the gills. For more notes, see the following descriptions. 2
The order Trichoptera contain the caddisflies. These insects spend their juvenile life in the water, then emerge as winged adults. As juveniles, they resemble grubs or caterpillars. Many species make cases out of woody debris, sand, or even small rocks which they fasten together with silk they produce, (slide 12 - the red arrow is pointing to the sand tube held together by silk that this burrowing caddisfly made) They can also use silk to make a pupal case or to modify their existing case during metamorphosis. Immature Lepidoptera (butterflies and moths) also produce silk; in fact, Lepidoptera is closely related to Trichoptera. The order Ephemeroptera contain the mayflies. These insects also spend their juvenile life in the water, then emerge as winged adults. As juveniles, they can be identified by their three tails located at the end of their abdomen (sometimes, however, they can have only two). The most distinguishing characteristics of this order is where the gills are located, along the abdomen (see arrows); the gills can look like feathers or leaves (see red arrow in presentation). 3
The order Plecoptera contain the stoneflies. These insects also spend their juvenile life in the water, then emerge as an adult. As juveniles, they can be identified by their two tails located at the end of their abdomen. The most distinguishing characteristics of this order is where the gills are located, along the thorax (see arrows); the gills can look like feathers or leaves (see red arrows in presentation). To distinguish Plecoptera from Ephemeroptera, remember that Plecoptera have their gills in their armpits, while Ephemeroptera have their gills on their abdomen. The order Odonata contain the dragonflies (see dotted arrow) and damselflies (see solid arrow). These insects also spend their juvenile life in the water, then emerge as winged adults. Both Damselflies and Dragonflies have a mouth with an articulated, extension arm that may cover face like a basket (see red arrow on dragonfly larvae slide in the presentation), or be flat against bottom of head, but they usually have teeth along the mandibles. In Dragonflies, the tip of the abdomen have triangular-shaped spines (see dashed arrow), while Damselflies have three leaf-like gills at the tip of their abdomen (see dotted arrow here and red arrow on damselfly larvae slide in the presentation). You can also see the wing pads (what will eventually become the wings) in the dragonfly slide in the presentation, the yellow arrow). 4
The order Diptera contain the flies. Some Diptera larvae are aquatic. They look like worms, though some may have distinct head capsules and some may not, and others may have false legs, but no Diptera larvae have true legs. The order Hemiptera contain the true bugs. Both juvenile and adult forms can be aquatic. The adults have three pair of legs and two pair of wings, the first pair having a partial leathery covering on the top half, while being membranous on the bottom half. They fold the second pair across their back forming an X shape (see dotted arrows). They also have a beak-like mouthpart (looks like a straw), which begins at the top of their head (see solid arrow). Juveniles look like adults, however, they do not have wings. Although, when the juveniles are about to change into their adult form, you may see wings pads (like the picture in of the dragonfly larva in the presentation) which will eventually become the wings. 5
The order Neuroptera contain the alderflies, dobsonflies, fishflies, snakeflies, lacewings, and antlions. Some of these insects spend their juvenile life in the water, then emerge as winged adults. Males and females can have mandibles which are usually sickle-shaped, the males being larger in size (see arrow and red arrow in presentation). Recently, Dobsonflies, Fishflies, Hellgrammites, and Alderflies were placed in a new order Megaloptera; however, for simplicity we have kept them in their original order Neuroptera. The order Coleoptera includes the beetles. Again, both adults and larval forms can be aquatic. The adults have three pair of legs, two pair of wings (the first of which has evolved into a hard covering called the elytra which protects the second pair), and variable mouthparts. The elytra comes together and forms a line down the middle of the back (see dotted arrows, red arrows in the presentation), compared to other orders whose wings overlap. Previously, students have described the antennae as looking like stacked balls, but they, too, are highly variable in size and shape. Beetle larvae look like worms with head capsules (see dashed arrow, red arrows in presentation) and true legs (found on the thorax) (see solid arrows, red arrows in presentation). 6
You might find pupae of different aquatic insects, sometimes within a case, sometimes with only a silken cocoon around it. These insects are holometabolists, which means they change completely from larval to the adult stage during metamorphosis (Diptera, Coleoptera, Neuroptera, and Trichoptera). Other insects are hemimetabolists which means they do not have a metamorphosis, but change gradually into an adult with each molt (shedding of the exoskeleton) (Ephemeroptera, Plecoptera, Hemiptera, and Odonata) or isometabolists which means they do not change at all, the young look exactly like the adults (rather like humans). 7
Examples of Graphs Aquatic Insect Orders in Different Habitats 18 16 14 run pool riffle number of insects per order 12 10 8 6 4 2 0 Coleoptera Diptera Ephemeroptera Hemiptera Neuroptera Odonata aquatic insect orders Plecoptera Trichoptera Unknown Aquatic Insect Adaptations in Three Microhabitats 18 16 14 run pool riffle number of insects per adaptation 12 10 8 6 4 2 0 skaters divers swimmers clingers sprawlers climbers burrowers Unknown adaptation 8
References Borror, Donald J., Charles A. Triplehorn, and Norman F. Johnson. 1989. An Introduction to the Study of Insects. Harcourt Brace College Publishers, New York. Lehmkuhl, Dennis M. How to Know the Aquatic Insects. 1979. WCB/McGraw-Hill, Boston. Merritt, Richard.W. and Kenneth W. Cummins. 1978. An Introduction to the Aquatic Insects of North America. Kendal Hunt Publishing Company, Dubuque, Iowa. Image References Folsom, Justus Watson. 1922. Entomology with Special References to its Ecological Aspects. 3rd Edition. P. Blakiston s Son & Co, Philadelphia. Miall, L.C. 1895. The Natural History of Aquatic Insects. McMillan and Co, New York. Osborn, Herbert. 1916. Agricultural Entomology. Lea and Febeger, Philadelphia. Ross, Herbert H. 1963. How to Collect and Preserve Insects. Circular 39. Natural History Survey Division, Urbana, Illinois. Wellhouse, Walter Housley. 1926. How Insects Live: An Elementary Entomology. McMillan and Co, New York. 9