The purpose of this lab exercise is to become familiar with the external and internal anatomy/morphology of the Eastern Lubber Grasshopper, Romalea guttata (also known as R. microptera.
The Eastern Lubber Grasshopper is classified as:
Insects exhibit one of two types of metamorphosis. Those with gradual metamorphosis change from egg to nymph to adult. In these insects (grasshoppers, roaches, true bugs), the nymphs look like miniature adults without wings, usually living in the same environment and eating the same food. Insects with complete metamorphosis go from egg to larva to pupa to adult (larva = ghost, specter; pupa = doll). Larvae of these insects look very different from the adults, usually live in a totally different environment and eat different food. The pupa is a “resting” stage where much transformation takes place. Probably the example of complete metamorphosis with which most people are familiar is that of a caterpillar (larva) changing to a chrysalis (pupa) then to a butterfly (adult). Silkworms are the caterpillars of Bombyx mori, a species of moth. As many, but not all, moths do, they spin cocoons prior to molting to a pupa/chrysalis, and humans have discovered that it is possible to unwind the silk thread that makes up their cocoons and weave it into cloth.
Members of Order Orthoptera have gradual metamorphosis.
Their life cycles consist of eggs, nymphs (which resemble the adults, as
well as sharing the same habitat, food, etc.), and adults. The same is true
for roaches, such as the mother and her new babies pictured here.
Other members of family Acrididae include other types of grasshoppers,
including the American Grasshopper pictured here.
While this American Grasshopper has long wings and can fly, the lubber
grasshoppers have short, stubby wings (hence the species name,
microptera, micro = small) and cannot fly.
As its common name implies, the Eastern Lubber Grasshopper occurs in the eastern United States, more specifically the southeastern US.
Nymphs (young) are typically black with a red or yellow stripe down the center of their backs. Adults have one of a few typical color patterns (phases). Some are a dull yellowish (greenish-yellow) with black markings, others are more orangish with black markings, and yet others are black with red or yellow stripes. Any/all of these yellow-and-black or red-and-black color patterns serve as warning coloration (aposematism — apo = from, off, away; sema, semato = mark, sign, signal, seal), a type of defense mechanism that advertizes their bad taste to would-be predators. They can also startle predators by forcing air out of their abdominal spiracles to produce a hissing sound and by secreting a bad-smelling and bad-tasting liquid.
|Type of Front Wing||Type of Back Wing||Other Notes||Photo|
|(endo, ento = within, inner; gnatho = the jaw), mouthparts within the head, primarily wingless, simple metamorphosis, no longer considered to be insects|
|none||none||(proto = first, original; ura = the tail)|
|none||none||(coll = glue; embola = a bolt or wedge) — collophore on bottom of 1st abdominal segm., for water uptake + furcula = jumping organ on ventral abdomen|
|none||none||(diplo = double, two; ura = tail) — group name refers to presence of two filaments arising from the posterior end of the body|
|(ecto = outside, out, outer) ectognathous — mouthparts stick out from head|
|(a- = not, without; ptero = wing, feather) primarily wingless, simple metamorphosis|
|none||none||(micro = small; corypha = head, top) — body more cylindrical than silverfish, small head with large compound eyes, body covered with scales|
|none||none||(thysan = fringe) — somewhat flattened body, three taillike structures on posterior end, body often covered with scales|
|winged (a few are secondarily wingless)|
= out, outside) — gradual metamorphosis, wing pads develop externally,
young are called nymphs (naiads if aquatic) —
Ephemeroptera, Odonata, and Plecoptera, which have aquatic naiads,
are said to be hemimetabolous (hemi = half).
|membranous||membranous, smaller than front wings||(ephemer = for a day, temporary) — aquatic naiads, winged subimago, then adult; very short-lived as adults|
long & narrow
long & narrow
|(odonto = tooth) — have “teeth” on mandibles, aquatic naiads; chewing mp; long & slender|
|(gryll = cricket; blatta = cockroach) — rare, nocturnal insects found in cold places like the edges of glaciers|
|(phasmato = apparition, phantom) — chewing mp; look like sticks or leaves, & well-camouflaged|
|(ortho = straight) — jumping back legs; chewing mouthparts|
|(manti, mantid, mantis = a soothsayer, a kind of grasshopper) — chewing mp; front legs adapted for catching prey|
|(blatta = cockroach) — chewing mp; legs adapted for running|
|membranous; same size as front (or absent)||(iso = equal) — light-colored; no “waist”; chewing mp; small size; social with castes, winged reproductives;|
|shortened = brachypterous
leathery, called tegmina or elytra
|membranous; folded under front wings (or absent)||(derm = skin) — forceps-like cerci at end of abdomen|
|(embi = lively, long-lived) — small; tropical & subtropical; silk glands in basal segment of front tarsus|
|membranous||membranous, “bottom” area folded under at rest||(pleco = twine, twist, braid, twisted, folded) — aquatic naiads|
|membranous or none||membranous or none||(zoro = alive, living, pure, strong; a- = not, without) — only wingless ones known when order was named; tiny; gregarious;|
|membranous or none||membranous or none||(psoco = rub small) — indoor in books = booklice; outdoors = barklice; small & soft-bodied; order name from gnawing habits|
|none||none||(phthir = lice) — ectoparasites (mostly on birds or mammals)|
|half-leathery, half-membranous hemelytra;
“X” when folded
|membranous||(hemi = half) — piercing-sucking mp;|
|(homo = same, like, alike) — piercing-sucking mp|
|similar to each other (unlike true bugs), held rooflike or tentlike over body when at rest|
|2 larval instars with internal wing development followed by 3rd or 3rd & 4th instars that are quiescent (prepupa & pupa) & have external wing pads; adults with or without wings||(thysano = fringe) — metamorphosis intermediate between gradual and complete; pupa sometimes with cocoon; tiny size|
| (endo = within, inner) — complete metamorphosis,
wing pads develop internally until pupal stage, young called larvae
|membranous||membranous||(neuro = nerve, sinew, cord)
— named for wing veins; dobsonfly larvae are aquatic; many prey
on other insects
(Photo © D.B. Fankhauser)
|hard, shell-like elytra||membranous||(coleo = a sheath) — chewing mouthparts; largest order with ~40% of all insects|
|males winged, females wingless||males winged, females wingless||(strepsi = twisted, a turning or twisting) — tiny; males free-living; females parasitic on other insects, may be legless|
|membranous||membranous||(meco = long, length) — tip of male’s abdomen curls up, resembling shape of scorpion’s (photo is female); long, snout-like head|
|none||none||(siphon = tube, pipe) — pupa in cocoon; blood-sucking; jumping; small & flat|
|membranous||modified as halteres||(di = two) — adults with sponging, cutting-sponging, or piercing-sucking mp|
|membranous, hairy, may be scaly||membranous, hairy, may be scaly||(tricho = hair) — larvae are aquatic, making protective cases of silk + stones, bits of leaves, etc.|
|bright color due to scales||bright color due to scales||(lepido = a scale) — siphoning mp in adults, chewing in larvae (caterpillar)|
smaller than front
|(hymeno = a membrane) — have a “waist”; chewing mp; many can sting; many social in colonies; often black & yellow bodies|
First, a review of the locations of “generic” insect segments and appendages would be useful. In this diagram, the segment labeled as #8 would be the first abdominal segment (labeled below as “A1”) and, in grasshoppers only (not true for other kinds of insects), bears the tympana (sing. = tympanum), #9 would be the second abdominal segment (labeled as “A2”), and #10 through 14 would correspond to A3 through A7. The segment labeled as #15 would be A8, and in female insects, bears the first “half” of the ovipositor. The segment labeled as #16 would be A9 and in females, bears the second “half” of the ovipositor, while in males bears portions of the male genitalia. The segment labeled as #18 corresponds to A11 and bears the cerci (sing. = cercus) in both sexes, while #19 is A12 and bears the styli (sing. = stylus) in males. All of these structures are discussed below.
Observe the external
anatomy of your grasshopper. Note that an insect’s body is divided into
three main sections: head, 3-segmented thorax, and abdomen.
On your grasshopper, find all body parts identified in this illustration.
Draw your grasshopper, and label those body parts on your
drawing. Optionally, if available, view (and draw) pinned specimens of
other insects, and find these body parts on those insects, too (caution:
pinned insect specimens are very fragile and easily broken if not handled
Ladybird Beetle As mentioned above, a number of dangerous or distasteful insects exhibit red-and-black or yellow-and-black stripes as warning coloration (aposematism — apo = from, off, away; sema, semato = mark, sign, signal, seal) to warn of their bad taste, stingers, etc. to deter would-be predators. Both Monarchs and ladybird beetles (ladybugs) taste bad.
|Yellow Jacket Wasp Model||Flower Fly Mimic||Locust Borer Beetle Mimic|
Other edible, non-venomous insects have taken advantage of
those bright color patterns, using mimicry to make potential predators
think they, also, taste bad or are dangerous. For example, it’s a big
mistake to tangle with a yellow jacket, but Locust Borers and flower flies
are pretty benign. Yet, due to their mimicry, they’re probably a lot less
likely to be eaten.
Another, often-cited example is Viceroy butterflies mimicking Monarchs, which
are known to taste bad, but it turns out that Viceroys, too, may not taste
all that good.
|Female Javanese Leaf Insect||Female Greater Angle-wing Katydid||Dead Leaf Butterfly|
Other insects depend on not being seen (camouflage) to
protect themselves from predators. Our local North American Walkingstick is
a good example, as is its relative, the Javanese Leaf Insect. Many species
of katydids and several kinds of butterflies also closely resemble leaves.
This dead leaf butterfly has its head down and to the right. What looks
like the petiole (“stem”) of the leaf on the upper left is actually pointed
tips on the hind wings. Look carefully and you may be able to see several
of its legs and its antennae.
Owl Butterfly © M. K. Busching Now, suppose you’re an insectivore (an animal that eats insects), walking through the tropical rainforest at dusk looking for some supper. “Hmmm... it smells like an insect, so let’s go check it out. Eeek! There’s an owl out there, and it’s getting ready to eat ME! Just look how big its eyes are! Forget supper, I’ve gotta get outta here!”
Well, chalk one up for the Owl Butterfly. Owl Butterflies sit with their wings shut, and so are fairly well camouflaged in the dappled light of the rainforest. When disturbed/alarmed, they suddenly open their wings, displaying the large eyespots that looks a whole lot like owls’ eyes. The centers of the wings and the body add to the realism by appearing to be the beak of the owl.
Examine your grasshopper paying special attention to its color pattern. Pokeweed is reported to be on lubbers’ list of favorite foods, and they, like many other insects, are able to sequester/store the toxic chemicals from pokeweed and the other plants they consume somewhere in their bodies (the exoskeleton is a common site for such storage). What does your grasshopper’s coloration tell you about it — into which of the above-mentioned categories does it fall?
A more detailed discussion of each body region (head, thorax, and abdomen) and its characteristics and appendages follows.
The top of the head is the vertex. The frons is the “face” area, bounded by the antennae and the top of the mouthparts. The gena is the cheek region below the eye and above the top, side edges of the mouthparts. The ventral portion of the frons is known as the clypeus. Below and attached to the bottom of the clypeus is a heavy flap, the labrum, which functions as the upper “lip.” Behind the maxillae is the labium, serving as the lower “lip,” a complex structure formed by the fusion of the paired second maxillae. More information on the mouthparts is included below.
Find all these parts on your grasshopper’s head, then draw in your lab
notebook and label them
Compound eyes — The compound eyes are composed of many, small,
hexagonal facets, called ommatidia (ommato = the eye). Each of these is a separate
“eye” and motion is detected by the interplay of light and dark across the
ommatidia. This photo is of the left compound eye on a female Chinese
Mantis. Her center
ocellus is also visible as a small brown “bump” to the left of the
The ommatidia are oriented such that their bottom ends come together and
often appear to
form a false pupil, visible through the compound eyes, as is seen in
this mantis’ eyes. Because the false pupil indicates location of the
bottom ends of the
ommatidia, down in the center, inside of the eyes, if you were really looking
at this guy in person, his false pupils would appear to change position as
you move your head. The false pupil helps the
insect to see better. Also, notice the three brown spots between his
antennae. These are individual eyes called ocelli (sing. = ocellus;
ocellus = a little eye)
which are discussed next.
Ocelli – Many, but not all, insects also have three individual
ocelli in between the compound eyes. This robber fly’s ocelli are
visible in the trough/valley between his/her compound eyes. Also, note the numerous facets of
the fly’s compound eyes.
This periodical cicada’s three ocelli are the three, small, brown spots
between the compound eyes.
Use a dissecting scope to observe your grasshopper’s eyes. Can you see the individual ommatidia? Also look carefully at the front of the vertex and the region where the vertex and the frons join. Does your grasshopper have ocelli?
Antennae (antenna = a sailyard) are modified appendages serving a sensory
function. Besides touch receptors, most insects also have chemoreceptors
(sense of smell) in/on their antennae. If available, observe and compare
antennae on various other types of insects.
|aristate||(arista = an awn, bristle)
— antenna often with 3 segments and having a filamentous arista
coming out of the side of the last/tip segment —
typical of many kinds of flies
These two little flies are mating (male on top). In this photo, their abdomens are off the picture to the left, and their heads are facing to the right. The antennae are yellow “lumps” off the fronts of their heads, and the aristae are the black filaments sticking out of them.
|capitate||(capit = the head) —
thinner antenna suddenly widening at the end into an enlarged, headlike
typical of butterflies, skippers, and a number of other types of insects
|clavate||(clava = a club) — antenna
gradually widening at the end into an enlarged or clublike tip —
|filiform||(fili = a thread) — the
whole antenna hairlike or threadlike, often longer in overall length —
typical of many types of insects
|flabellate||(flabella = a fan) — each
segment enlarged on one side into a platelike or leaflike projection,
giving the whole antenna the appearance of a fan —
|geniculate||(genicul = the elbow, knee)
— the basal segment is elongated, and the other segments held at an angle
to that segment, giving the antenna an overall elbowed appearance —
typical of ants, bees, and many other Hymenopterans
|lamellate||(lamell = a small plate) — a thinner antenna with a few of the tip segments enlarged into platelike or leaflike projections —
typical of Scarab beetles
|moniliform||(monil = a necklace, string
of beads) — each segment of the antenna rounded and beadlike —
This Milkweed Leaf Beetle’s antennae really are only half-way moniliform, and aren’t really rounded into totally bead-like shapes.
|pectinate||(pectin = a comb) — each
segment with one or two (bipectinate) lateral projections giving the
antenna an overall comblike appearance —
typical in some kinds of moths and a few other kinds of insects
|plumose||(plumo = a feather) — each
segment with numerous, filamentous projections, giving an overall
feathery appearance —
typical in male mosquitoes and some other kinds of insects
|serrate||(serrat = a saw) — antenna
with each segment pointed on one side, giving an overall appearance that
the antenna is toothed along the edge like a saw —
|setateous||(seta = a bristle) — the
whole antenna thin and bristlelike, shorter in length —
typical in dragonflies, damselflies, and cicadas
|stylate||(stylo = a pillar, stake,
column, a pointed instrument) — antenna often 3-segmented, with the tip
(not side) of the last segmented becoming/bearing a thin, threadlike
typical in some kinds of flies
Examine your grasshopper’s antennae. Based on this list and photos (above), which type of antennae does the grasshopper have? If not already part of your drawing of the grasshopper’s head, draw your grasshopper’s antennae. Include a label telling which kind of antennae these are.
Mouthparts – There are four “types,” four layers, of mouthparts. These are listed here from front to back. The labrum is not considered to be an appendage, but the mandibles, maxillae, and labium are appendages of segments 2, 3, and 4, as shown in the diagram, above.
While chewing mouthparts are considered the “primitive” or “ancestral” form, in many other types of insects, including true bugs, butterflies, etc., the same four structures are present, but may be highly modified for other diets and methods of feeding. Some of these types are listed below.
Carefully remove each mouthpart from at least one side (left or right – both is OK, too) of the head/mouth by using a forceps to pull it out from the base in order to observe it more closely. As you remove each part, first examine it carefully to see how it fits and to better view the remaining mouthparts. Then, after each is removed, use a dissecting scope to get a better idea of what that mouthpart looks like. Draw that mouthpart, labeling its sub-parts (for example, the palpi. Once you familiarize yourself with the mouthparts of the grasshopper, also view and draw the mouthparts of any other insects that may be available. In addition to chewing mouthparts, also look for insect specimens with other types of mouthparts.
|mandibulate, chewing||grasshoppers, roaches, mantises,
this is thought to be the most primitive form from which all the others are derived
|piercing-sucking, haustellate||mosquitoes, true bugs, cicadas,
these can pierce the host tissue (plant or animal) and suck up fluids; may secrete digestive enzymes, first, to liquify solid food;
in true bugs and cicadas, the mouthparts are collectively called a beak or proboscis
if needed, flies will first secrete digestive enzymes to liquify their food, then all food, in a liquid form, is sponged up by the mouthparts
these cut a host’s skin, then sponge up the blood that comes out (this one wouldn’t hold still long enough for a mouth picture)
|proboscis, siphoning||butterflies and moths
mouthparts are called a proboscis and function like a soda straw
bees need to chew on honeycomb to shape it, and also lap up nectar/honey; “scissor-like” mandibles can be seen at the base/bottom of the head, on the left, while the long tongue sticking out is used to lap up honey
The thorax includes 3 body segments: the prothorax, mesothorax, and metathorax. Each of these segments bears a pair of legs. Additionally, the meso- and metathorax frequently each bear a pair of wings (which are not considered to be appendages).
Each thoracic segment has a sclerotized (hardened; sclero = hard) dorsal portion, the notum, (nota, notum = the back) — specifically pronotum, mesonotum, and metanotum — and a sclerotized ventral portion, the sternum, (stern = breast, breastbone) joined by a lateral membranous area.
Compare the flexibility of the thorax versus the abdomen. Why do you suppose this is? (Hint: To where do you think the muscles used in walking attach?)
The parts of an insect leg are named such that the locations of these
parts roughly correspond to the locations of the parts of the human leg.
The small segment that attaches to the body is the coxa (coxa
= hip), followed by another small segment, the trochanter
(trocho = wheel, disk — in reference to the ball at the top of the
femur in humans), then the larger femur (femur = thigh), the
tibia (tibia = flute, the shin bone) and finally, the series
of smaller segments farthest from the body are the tarsi
(tarsus = the ankle).
On the ventral surfaces of the tarsi, note the whitish (or at least, lighter
colored) tarsal pads. These “suction cups” are controlled by hydraulic
pressure within the animal’s body and serve to cling to objects. Also note
the tarsal claws on the last segment. Different insect species have
from two to five tarsal segments per leg and some have differing numbers of
tarsi on the pro-, meso-, and metathoracic legs.
|cursorial: running||cockroaches, tiger beetles
(curso = run, a runner)
|fossorial: digging||mole cricket, cicada nymphs
(-fossor = a digger)
As can barely be seen on these cicada skins, the front legs of cicada nymphs are modified for digging.
|gressorial: walking (vs cursorial = running)||grasshopper front legs, milkweed leaf beetle
(gress = walk, walking)
|natatorial: swimming||diving water beetle, giant water
(natan = swimming)
Notice how especially the hind leg on this giant water bug is broad and oar-like for swimming. The front legs, by the way, are raptorial.
|raptorial: grasping prey||mantis, water strider
(raptor = seize, plunder, a plunderer)
Notice how “Mom Mantis” can fold her tarsi back out of the way to protect them while manipulating her prey/food.
|saltatorial: jumping||grasshopper, katydid, camel cricket,
(salta = leap, dance)
This delicate little lady is a tree cricket.
|scansorial: climbing||Harlequin Beetle
(scansor = climb) elongated joints with large tarsal claws; female Harlequins’ legs are a bit shorter than those of the male; when mating, the male must have front legs that are long enough to reach around the female and grab hold of the tree trunk.
|Honey bees’ legs are highly specialized for a number of important functions related to gathering pollen. See below for a labeled and annotated illustration.|
|pulvillus (pulvilli), a type of tarsal pad||Many flies (Order Diptera) have a pair of pads attached at the bases of the tarsal claws. In this fly, they are visible as the pair of white pads on the end of each foot.|
|fruit fly male sex comb||Male fruit flies have a black sex comb on their first prothoracic tarsal segment. These are used to grab the female’s abdomen and/or wings as part of their courtship prior to copulation.|
|suction disc on predaceous diving beetles||Not visible in this picture, but male diving beetles (Dytiscidae) have large “suction discs” on their front tarsi. These are used to hold onto the smooth, shiny elytra of the female during mating. Also notice that the hind legs (one sticking up in the photo) are flattened and fringed with hairs to serve as “oars,” enabling the beetles to swim. Note the air bubble (most of which is under the elytra and not visible), portions of which are visible, giving the body a silvery color.|
|tympanum on katydids
|Katydids and crickets that sing have a tympanum (tympanum = a drum) on the tibiae of their front legs. This organ enables them to hear. In this photo, this katydid nymph’s tympanum is the brown spot just below her front “knee.”|
Examine and draw your grasshopper’s legs. How are the grasshopper’s three pairs of legs similar, and how are they different? How many tarsi does a lubber have on each of its legs (make sure your drawing is accurate)?
As time and specimens allow, observe legs on a variety of pinned insects. Look for and draw legs from as many of the following categories as are available to examine.
If available in lab or later, while your class is on a field hike, observe a live insect walking. Note that it moves its legs in sets of three (front and back on one side and middle of opposite side) so that it is always resting on a tripod (the most sturdy and secure base of support).
Insect wings are modified in a number of ways, as listed in this table.
|apterous||(a- = not, without)
This refers to any insect in which wings are lacking. Again, this occurs in insects in many groups where close relatives have full-length wings, and in that case, such insects would be called secondarily apterous. In other insect groups, such as whole orders whose members have never had wings, they are said to be primarily apterous.
|brachypterous||(brachy = short)
This refers to an insect that has short wings — it occurs in insects in many groups where close relatives have full-length wings. Since “brachypterous” refers to the length of the wings, it may be combined with other terms such as elytra or tegmina.
(photograph of female Australian Walkingstick © M. K. Busching, retired Curator of Invertebrates at the Cincinnati Zoo)
(elytr = a sheath, cover)
the hardened forewings characteristic of Order Coleoptera
|halteres||flies, mosquitoes, crane flies
(halter = a leaping weight) hind wings modified as knob-like balancing structures — characteristic of Order Diptera, and since they are often tiny and not easily visible, dipterans appear to have only two wings
(hemi = half)
wings whose close (proximal) portion is leathery and whose farther (distal) portion is membranous, and which are held such that they form an “X” over the insect’s back — characteristic of Order Hemiptera
|membranous||honey bees, dragonflies
membranous wings are typical of a wide variety of insects
|pictured wings||typical especially in some types of
flies (Diptera) which have spots or bands on their wings — also true of
some types of dragonflies
Picture-wing flies often use their wings in a signaling display as part of their courtship ritual.
|scale-covered wings||butterflies, moths
wings that, underneath, are membranous, but they are covered with scales, which may be brightly colored — characteristic of order Leipdoptera;
some members of Order Trichoptera (caddisflies) also have scales on their wings
This photo shows a Cecropia Moth, a very large, local moth, and a close-up of a portion of one of her wings, showing the scales.
|tegmina||grasshoppers, katydids, crickets,
cockroaches, walkingsticks, mantises
(tegm = a cover)
the leathery forewings found in Phasmidae, Orthoptera, Mantodea, and Blattaria
In some species of insects, the wings of the males and females
differ. In katydids and crickets, the tegmina of the males are broader and
rounder and include a stridulatory area consisting of a file on one one wing
and scraper on the other. These are rubbed together to produce sound. The
tegmina of the females lack those organs, and may be thinner and more pointed,
posteriorly, than those of the males. In this photograph, a female tree
cricket is on the left, and a male on the right.
In Monarch butterflies, the males have a small scent gland,
near one of the veins on their hind wings, while the females do not have
this structure. In this photograph, the hind wings on top are from a female,
while the set of hind wings, below, is from a male.
As time and specimens allow, view and draw a variety of wings found on different types of (pinned) insects, looking for as many of the types listed above as are available. Which type(s) of wings does your grasshopper have?
The abdomen clearly shows its segmentation. Each segment has a sclerotized dorsal portion, here called the tergum, (terg = back;) and a sclerotized ventral sternum (stern = breast, breastbone), again joined by a lateral membranous area. (Note: you will also see the words “tergite” and “sternite” used.)
Spiracles (spiracl = an air hole) occur along
the sides of the abdomen, between the edges of the sternites and tergites.
They are located in small, sclerotized regions, one pair per segment.
Look closely to see the opening of the spiracle in each segment and the lid-like structure that controls the aperture of the spiracle. In hot, dry weather insects can close their spiracles to help avoid water loss (unless they need to take in more oxygen). Observe the structure of the spiracles under the dissecting scope.
One abdominal structure that is unique to grasshoppers is the tympanum (tympanum = a drum). In general, those types of insects which produce sound also have some structure which allows them to hear sound. In grasshoppers, this auditory structure consists of a pair of tympana located on the sides of the first abdominal segment. True to their name, these detect sound by vibrating like a drum head.
Make sure to include the tympanum and spiracles on your grasshopper illustration.
Male Lubber Grasshopper, Posterior Tip of Abdomen
Female Lubber Grasshopper, Posterior Tip of Abdomen
Finally! Now you get to figure out whether your grasshopper is a male or female. Examine these photographs and compare them with your grasshopper to determine which you have. Also, look for, draw, and label the structures listed below.
Determine your grasshopper’s sex. Draw and label pictures of the “back ends” of both sexes (so you can remember who’s who). Examine and compare the ventral side of the subgenital plate of a male and female grasshopper. How large and distinguishable is/isn’t the subgenital plate? Is there a difference between males and females?
Longitudinal Cuts To expose the internal structures, if not done already, first remove the wings and legs. Then carefully make two shallow, longitudinal (front to back) cuts through the dorsal (back) body wall of the abdomen and thorax about ⅛ in. (3 mm) to either side of the midline. Carefully remove the dorsal piece (save) — caution: the heart and aorta are right underneath and may “stick to” the piece you are removing. Pin the sides open onto the dissecting tray to better expose what is inside.
Silkworm Heart, Close-up
Heart and Aorta This may come off with the top flap or it may stay on the inside. It is a dorsal tube along the midline and lies on a thin, muscular sheet which may come off with the tergum. Blood is pushed from posterior to anterior and out into the head cavity. The blood flows from there back through the body, thus this is an open circulatory system (make a sketch in your notebook of the blood flow pattern). In some insects, such as a last instar (“mature”) silkworm caterpillar (examine if available), it is possible to see the heart beating. In the silkworm photographs, above, the heart/aorta is the darker gray line up the center of the back.
Male Lubber Grasshopper Digestive System
The parts are listed below from front to back. Note: the digestive systems of many insects are somewhat- to highly-modified from this general plan.
Compare your grasshopper with one of the opposite sex being dissected by your classmates to observe the reproductive systems of both sexes.
This is a fine network of tracheal tubes bring oxygen
directly to the
tissues, thus in most insects, the blood does not function in carrying
oxygen and has no hemoglobin (some have hemocyanin which is also based on
porphyrin, but with copper in the center, and that gives their blood a blue
or greenish color). The respiratory system appears as
silvery-white threads of various diameters.
As in the first photo, small tracheal tubes extend from the spiracles
into the body and unite with one of the two (left and right) longitudinal
tracheal trunks that extend the length of the body (Also in the photo,
port-hole-looking structure is the inside of the tympanum.).
The second photo is a close-up view of one of the incoming trachea tubes. Notice the barely-visible rings around that tracheal tube to support it, similar in function to the rings that support our trachea and help to keep it open.
From the longiudinal tracheal trunks, many smaller tracheal tubes branch off to deliver air to all the body organs.
As in this third photo, make a wet mount of and observe a portion of a
tracheal tube under the microscope to see the thickened rings of tissue
(analogous to the rings you can feel in your own throat or some vacuum
cleaner hoses) which strengthen it.
All muscles lie within the exoskeleton and attach to it to pull it in some direction (as in our bodies, muscles can only contract and pull — muscles cannot push). Muscle tissue is probably most visible in the thorax where it controls walking and flight. Interestingly, there are no muscles in insect wings. Flight is controlled by changing the shape of the thorax, the sclerotized sides of which act like fulcrum points under the wings. Vertical muscles pull the notum down, so the wings, stretched across the fulcrum points, go up like a teeter-totter. Then, longitudinal muscles pull the segment together, front-to-back, which causes the notum to buckle upwards, and that, in turn, causes the wings, still stretched across the fulcrum points, to go down. There are several other sets of muscles involved in angling the wings for lift and steering, and the actual path of the wings is a figure-eight. Many insect movements are also brought about by hydraulic pressure: by forcing blood/body fluids into certain areas, movement is brought about.
Carefully remove (or pull to one side) the digestive, reproductive, and respiratory systems. Under them, you should see a thin muscle sheet. Gently remove that muscle sheet. Examine, draw, and label pictures of the nervous system.
As in the photo below, the nervous system (NS) lies on the ventral surface of the body covered by that thin muscle sheet. The NS is a yellowish-white, double, ventral cord running between small ganglia of nerves in each segment. This NS is very primitive with each segmental ganglion exercising much control over “its” segment. As can be seen in this photo (and hopefully, in your grasshopper), the ventral nerve “cord” actually consists of two parallel nerve cords.
Notice, as in the following photo, that the thoracic ganglia are larger than those in the abdomen. Why do you think this is? Notice that anterior to the “last” large thoracic ganglion, the two strands/halves of the nerve cord split and separately continue anteriorly.
Also, to the sides of the nerve cord, where the nerve cord starts to split, in the anterior portion of the thorax, there are grape-like clusters of small, rounded, “knobby” structures that are the salivary glands.
In the lower head, there is a subesophageal ganglion. Then the double cord splits and goes around either side of the esophagus, meeting at the supraesophageal ganglion (brain) which controls eyes, antennae, etc. In the following photo (and its enlargement, below), one of the circumesophageal connectives is barely visible.
Note that whereas the vertebrate NS is dorsal and a hollow infolding of ectoderm tissue, the arthropod NS is ventral, solid, and mesodermal in origin. Although most insect behavior is instinctive, some learning ability is present. Supposedly, roaches can be taught to run a simple “Y” maze.
Make sure you have all of the following in your lab notebook: