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 Body
Systems
Bug bodies are very different to our bodies. Bugs eat, excrete, breathe, and
sense their world as we do, but in very different ways.
Skeleton
Bugs have their skeletons on the outside of their bodies. The hard, segmented
cover is called an exoskeleton. Made of chitin, it is strong but also light and
flexible. The exoskeleton provides support and protection, and has evolved into
many shapes, textures and colours. It is covered in a thin layer of wax, which
waterproofs the animal and stops it losing water from its body. The segments
are joined together by soft tissue to allow movement.
Digestion
You have a mouth that delivers chewed food to your stomach and intestines. Bugs
have a long and tube-like digestive tract, often made up of three sections,
each with different functions. Food travels from the mouthparts down the
digestive tract, with most of the ‘chewing’ done in the first section or
‘foregut’.
Circulation
You have a ‘closed blood’ system. Your heart pumps blood through arteries and
veins around your body. Bugs have an ‘open blood’ system in which a single tube
with a series of pumps—or hearts—moves blood in one direction along
its length. Blood ‘washes’ over the organs and returns along the tube.
Excretion
Your blood is cleaned of wastes as it is pumped through your kidneys. Bugs have
malpighian tubules that float around inside the body cavity, extracting waste
products from the blood that washes over them.
Respiration
You have a nose that leads to two large air sacs—your lungs. Insects and
most spiders breathe through a series of openings, called spiracles, which are
situated along their bodies. The air travels down tubes, delivering oxygen to
all parts of the insect’s body. The spiracles can also be sealed, allowing the
insect to stay dry, or to prevent moisture loss in hot conditions. Most spiders
also breathe through spiracles. A few spiders have simple lungs called ‘book
lungs’.
Nervous System
You have a brain that is connected to your spinal cord along your back. Your
brain controls the activities throughout your body. Bugs have a nerve cord on
their underside with ‘mini-brains’, or ganglia, along its length. These
mini-brains can work independently. If an insect loses its head, it does not
die immediately but eventually starves to death because it can’t eat.
digestion:
The breakdown of food into smaller particles (by the action of enzymes) that can be absorbed by the body.
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