The arthropod collections allow the students to get a taste of the diversity of these creatures even in urban environments. We will attempt to identify each specimen collected to its genus and species; however, if they recognize the major classes of the insects then they will have achieved a good amount.
One of the arthropods classes we will study are the insects. The other classes such as the arachnids (spiders, ticks etc) and crustaceans (generally aquatics species such as the crabs) we will ignore for now.
The shear numbers of insect species is an indicator of how successful they have become. There are over 900,000 known species of insects versus 38,000 known vertebrate species. Representatives of these animals in almost any land climate zone except the Antarctic zones. They are small animals with three body parts head, thorax and abdomen six legs a pair of antennae. Most of them contain a double pair of wings (With the exception of the fly family which have one pair). Their body is supported by a tough exoskeleton. This tough outer skeleton is called the cuticle. The cuticle is composed of a layer of wax and chitin. These materials make the cuticle impermeable to water. It acts as a medieval suite of armor, protecting the insect from dilute acids, alkalis and organic solvents. Thus designing an insecticide is no simple matter.
The most complicated feature of insects is the mouth. There are a two basic variations in the structure and purpose of insect mouths. First is the very primitive mandibulate version used for crushing and chewing. The other is the haustellete version used for sucking.
Insects play an extremely valuable role in any ecosystem. The relationship between plants and insects is so close it is doubtful whether the evolution of the angiosperms could have proceeded without them. Plants and insects have evolved to the point where often one species of plant will be totally dependent upon a single species of insect to survive. Humans have become dependent upon these animals as well. We depend upon them to pollinate our fruits, vegetables and field crops. Mention could be made as well of the predatory and parasitic varieties that help to keep down the insects that could cause unfathomable damage to our agriculture.
The major classes of insects we expect to find
Has two pairs of wings. The fore wings are hardened to form a protective cover. The hind wings are membranous. Mouth parts are mandibulate. Larvae (also called grubs) usually eat the same food as their parents.
– Only has one pair of wings which are membranous. Mouth parts are designed for the food source they seek. Larvae (called maggots) prefer moist areas. Examples include the horse fly, house fly, crane flies mosquitoes, midges and the fruit fly (which we will use later in genetics)
or true bugs. These insects have two pairs of wings. The forewings are partly thickened the hind wings are membranous and fold over the body. Their young are nymphs in that they resemble adults. Examples include the water bug, bed bug and stink bug
- These are the bees, ants and wasps. Have two pairs of membranous wings. The forewings are much bigger than the hind wings. Wings are absent in ants unless for reproduction phase. Most varied of orders in terms of feeding. Bees gather pollen, some feed on nectar, others are predatory or parasitic. Larvae usually do not eat same type of food as adults
- Have no wings unless in the reproductive phases. Tend to be found in the wood and the ground and are social. Examples include Termites
Two pairs of wings of differing size and shape. Mouth parts are haustellete and specifically designed for siphoning. Generally feed off the nectar of flowers Larvae are called caterpillars and do not resemble adults. Examples are the moths and butterflies.
– Winged insects with gradual or simple metamorphosis. Examples of this call would be the grasshopper, crickets and cockroaches
- Have two pairs of membranous wings about equal in size. Mouth is designed for chewing. Examples of this class are the dragonflies and damselflies