Nicole Jones of Green Island School asks :-

What colour is spider blood?

Simon Pollard, an invertebrate zoologist at Canturbury Museum, responded.

All the living cells that make up our body and the body of a spider need a constant supply of oxygen to survive and this is pumped by a heart through blood vessels. In the case of people, a special protein called haemoglobin, which is stored inside red blood cells, carries oxygen molecules. Our blood is red because the haemoglobin molecule contains oxygenated iron. Spider blood or haemolymph, is blue because the oxygen-carrying protein haemocyanin contains oxygenated copper. Haemocyanin is not stored within blood cells, but instead floats freely in the haemolymph.

Spiders have a very simple heart, which is in their abdomen, and is little more than a tube with a couple of valves to make sure the blood flows in one direction. When muscles attached to the heart contract, the tube enlarges and it fills with fluid. The muscles then relax and blood is forced out of the heart and around the body of the spider. The heart beat generated by the contraction and relaxation of muscles varies depending on what the spider is doing. For example, a wolf spider has a resting heart beat of about 50 beats a minute, but this will increase to about a 180 beats per minute if it is running.

With a microscope, you can easily see the heart beating beneath the thin wall of the abdomen in light-coloured spiders. And a racing heart will be a tell-tale sign that the spider would like to be running away!