Centipedes, millipedes, and insects
The Class Chilopoda
This taxonomic class includes 20 families and more than 2500 species of centipedes, all terrestrial.
Most centipedes are small, but a few can attain a length of up to 10 inches (25 cm). Centipedes have
bodies are made up of a chain of many (up to 177) flattened segments. With the exception of the
segment behind the head and the last body segment, each segment has a single pair of appendages
(legs). The appendages of the first body segment have been modified to form large, poisonous fangs
that are used to capture prey. The bite of a large centipede, however, can be painful to an adult and
dangerous to a small child.
Scutigera (centipede):
The Class Diplopoda
Millipedes comprise this class containing some 8000 species. Bodies of members of this class are
made up of numerous segments. Millipedes lack poisonous fangs and do not bite. Predators are
discouraged by the millipede's rolling into a defensive ball. Production of poisonous or foul-smelling
substances also serve to dissuade any would be predators. Most millipedes are apt burrowing
herbivores or scavengers.
Tachypodoiulus (millipede):
The Class Insecta
Insects are the largest group, with probably over one million identified and named species (and
undoubtedly a greater number as yet unknown to us). Insects live in almost all terrestrial and
freshwater habitats, with a few species living in the oceans. Many insects have some thoracic
appendages modified for flight. Insects are important as pollinators for flowering plants, as well as for
the damage they do annually to crops, and the diseases they transmit (malaria, some forms of
encephalitis, Dengue Fever, the West Nile virus, etc.)
Anatomy of the insect body:
Insects display a wide variation in body styles, although there seems to be a size limit on the insect-
style of body organization. Common features shared by most living insects include:
- body composed of three tagmata:
- head
- thorax
- abdomen
- one pair of relatively large compound eyes
- usually three ocelli located on the head
- one pair of antennae on the head
- mouthparts consisting of a labrum, a pair of mandibles, a pair of maxillae, a labium, and a tonguelike
hypopharynx
- two pairs of wings derived from outgrowths of the body wall
- three pairs of walking legs
Insects have a complete, complex digestive system. They exchange gases through a tracheal system,
with external openings called spiracles dividing into finely branched tubules that carry gases directly to
metabolizing tissues. Aquatic forms may exchange gases through the body wall or may have various
kinds of gills. Excretion of nitrogenous waste takes place via Malpighian tubules. The nervous
system of insects is complex, including a number of ganglia and a ventral, double nerve cord. Sense
organs are complex and acute. In addition to ocelli and compound eyes, some insects are quite
sensitive to sounds, and their chemoreceptive abilities are excellent.
Mouthparts of insects:
lr – labrum
md – mandibles
mx – maxillae
lb – labium (another pair of maxillae grown together)
There are generally two growth patterns:
- Insects with incomplete metamorphosis - Hemimetabolous – from fertilized eggs develop nymphs,
which are without wings, and they live in different environment then the adult individuals. They molt
few times till they reach adult phenotype. Dragon flies, cockroaches, crickets and locusts, mantis, lice,
termites, heteroptera
- Insects with complete metamorphosis – Holometabolous – from fertilized egg develop larva. It
molts few times and after this it reaches other stage – pupa, where it changes into adult individual.
After development pupa breaks and adult individual – imago is created. Beetles, hymenoptera (bees,
hornets, bumblebees, wasp, ants ), diptera (flies, mosquitoes), fleas, butterflies,
Insects are very valuable to us. While insects eat our food, feed on our blood and skin, contaminate
our dwellings, and transmit diseases, we could not exist if they were not here. Insects are a vital part
of our ecosystem, functioning in:
- pollination of many flowering plants
- decomposition of organic materials
- recycling of carbon, nitrogen, and other essential nutrients
- control of populations of harmful invertebrate species (including other insects)
- direct production of certain foods like honey
- manufacture of useful products such as silk and shellac
Main sources: On-Line Biology Book, Michael J. Farabee; Encyclopedia of Life (www.eol.org)
