[dentstudent (OP)]

I'm currently reading a book entitled "A world without bees" which gives a complete overview of the historical disappearances of bee colonies and the suspected reasons. One of the parasites discussed is the Varroa mite which sucks the blood of the bee. This raised a question that I'd never even considered, and that is the size of the veins and arteries inside a bee, and the blood cells therein, and how tiny they must be. So, how different is bee blood to human blood? Do they have the same kind of blood but with smaller "bits"? And what about the heart - how different is that to a human heart? Does it have 2 chambers, too? Does it "lub-dup"? And then of course there are all the other organs! I guess that I'm so used to considering these on a human scale, that it's almost inconceivable that it's possible to fit all that in to something as small as a bee!

[lyner]

Bees and other invertebrates are small enough not to need a blood circulation system to help with their respiration. They have a system of tiny tubes called spiracles which let air circulate around their cavities. The oxygen and CO2 just get in and out by diffusion. This is one thing that  limits the possible size that insects can attain. A proper circulatory blood system can bet the gases around much better but it would be overkill for such small creatures. You know how 'lazy' nature can be.

[chris]

Bees don't actually have blood cells. Insects instead have a structure called a haemocoel, which is effectively a bag of blood in their abdomen. The pulsations of the abdomen you see them making serve two purposes - 1) to move air in and out of the spiracles and 2) to move the haemocoel - this helps to maintain the gaseous diffusion gradient that brings in oxygen and rejects CO2.

Chris