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Morphology of the Lubber Grasshopper
Morphology is the study of external form.The lubber grasshopper (Phylum Arthropoda, Class Insecta,
Order Orthoptera) is a useful specimen to demonstrate generalized morphology of insects. Knowledge
of the basic morphology will enable you to appreciate the many morphological specializations
exhibited by insects you will see later in this lab.
Use the descriptions and figures to locate underlined structures and label Figure III, p. 4.
EXOSKELETON AND BODY REGIONS
Note the hard, outer plates covering the insect. This is the exoskeleton which serves many functions
including muscle attachment, protection and water retention. Grooves called sutures can be seen
between the plates of the exoskeleton. These indicate internal projections of the exoskeleton for
muscle attachment. The exoskeleton may undergo sclerotization (hardening) and can be extremely
strong.
The body is divided into 3 regions: the head, the thorax and the abdomen. The head is specialized
for feeding and sensory functions. The thorax (3 segments) is specialized for locomotion and the
abdomen (11 segments) performs digestive, respiratory and reproductive functions.
THE HEAD (Refer to Figure I)
The head is a hardened capsule, attached to the thorax by a membranous neck, allowing movement.
Locate the underlined structures and regions on the head and label them on the figures.
Identify two large compound eyes and the two
antennae. Between the base of the antenna and the
compound eye is a much smaller ‘simple eye’, called
the lateral ocellus. Locate the lateral ocellus on each
side. There is also one median ocellus between the
antennal bases on the front of the head. (These ocelli
may be difficult to see). The region between the
antennae on the front of the head is called the frons.
The top of the head is the vertex. The prominent
horizontal suture across the middle of the front of the
‘face’ is called the epistomal suture. “Epistomal”
means “above the stoma” or “above the mouth”.
Immediately under the epistomal suture is a plate
called the clypeus and below this is the “upper lip”,
called the labrum. Directly behind the labrum are
the extremely hard mandibles, used for ripping and
macerating vegetation. Behind the mandibles are the
paired maxillae, each with an appendage called the
maxillary palp, and behind the maxilla is the
labium, which bears 2 labial palps. The maxilla and
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labium aid in tasting and manipulating food. The mandibles, maxillae and labium are easier to see
from a side view, rather than a front view.
THORAX (Refer to Figure II)
The thorax is divided into 3 segments: the prothorax (first), mesothorax (middle) and the
metathorax (last). The prothorax is completely covered by a large shield-like plate called the
pronotum. Each segment bears one pair of legs. The meso- and metathorax each bear
one pair of wings. The wings of the lubber are reduced; it is flightless. The metathoracic pair of wings
are folded and hidden beneath the mesothoracic pair.
Plates of the exoskeleton are named for their location (dorsal, ventral or lateral). Dorsal (‘on the top’)
plates are called tergites. Sternal (‘on the bottom’) plates are called sternites. Lateral (‘on the side’)
plates are called pleurites. Pleurites are only present on the thorax, while tergites and sternites are
present on both the thorax and the abdomen. Note the sutures in the pleurites, indicating inward
projections for muscle attachment for the large muscles which move the legs and wings.
Figure II – Plates of the Exoskeleton
LEGS
The insect leg is jointed (Arthro- poda) and consists of 5 segments: the base which connects to the
thorax is the coxa. The trochanter is the next segment which is very small and barely visible laterally.
Next is the long femur; note the enlarged femur on the 3rd pair of legs and relate this morphological
adaptation to the function of the 3rd pair of legs. The next long leg segment is the tibia. The last
segment is the tarsus which consists of 5 subsegments and a terminal claw.
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ABDOMEN
There are 11 abdominal segments (although in most more specialized insects this number is greatly
reduced). The last (11th) segment appears triangular and bears 2 small sensory appendages called
cerci. The 9th and 10th segments appear fused in part and may be difficult to distinguish as 2 separate
segments. The first segment is hidden under the short wings. By lifting the wings you will see an
opaque round membrane on each side of this first abdominal segment. This is the tympanum which
functions in hearing.
Recall that dorsal exoskeletal plates are called tergites and ventral plates are called sternites. Identify
these on the abdomen. On the lower edge of most of the tergites, near the sternites, locate small,
indented, sclerotized circles. These are spiracles, openings for air movement in and out. Between the
sternites and tergites observe the flexible membrane which allows the abdomen to expand and contract.
REPRODUCTION
The female can be identified by four, large heavily sclerotized projections which make up the
ovipositor. The ovipositor is used to make a hole in the ground for the eggs and to direct them into the
hole. The ovipositors of insects show enormous variation in form, depending on where the eggs
are laid. Some ovipositors are modified enabling them to inflict a painful sting (Order Hymenoptera bees, wasps and ants).
The male aedeagus (penis) is usually telescoped inside the abdomen and thus is normally not very
obvious. Examine a demonstration specimen in which the aedeagus is extended and notice its
complicated structure. These reproductive structures also show enormous variation among different
groups of insects and even differ from species to species. Therefore they are often used as important
taxonomic characters.
Generally (there are many variations) when insects copulate, the male transfers sperm through the
aedeagus into an internal pouch of the female. The female stores the sperm in another internal
chamber until she is ready to lay eggs. The eggs are fertilized by the stored sperm as the female lays
them. The ovipositor, as mentioned before, is highly specialized to prepare and place the eggs in the
location appropriate for that insect species.
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Figure III – Structures to Know on the Lubber Grasshopper
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