Why do caterpillars have yellow blood?
Like human blood, bug blood carries nutrients and hormones to the insect's cells. The greenish or yellowish color of insect blood comes from the pigments of the plants the bug eats.
The reason insect blood is usually yellowish or greenish (not red) is that insects do not have red blood cells. Unlike blood, haemolymph does not flow through blood vessels like veins, arteries and capillaries. Instead it fills the insect's main body cavity and is pushed around by its heart.
If you are in an emergency situation with poisoned caterpillars, click on this sentence NOW. This green fluid is close to the same color as a caterpillar's hemolymph (blood). It is easy to tell the difference. Hemolymph dries to a dark color, nearly black, in less than five minutes.
Technically, caterpillars do not have "blood" per se, but they have hemolymph, which is similar to blood in that it is pumped throughout their bodies by heart-like nodes.
mosquito have yellow colour blood but it bleeds red colour blood ?
Sea cucumbers have yellow blood due to a high concentration of a yellow vanadium-based pigment called vanabin. Some members of the phylum Annelida (segmented worms and leeches) have a greenish respiratory pigment called chlorocruorin.
Jaundice occurs when there is too much bilirubin (a yellow pigment) in the blood—a condition called hyperbilirubinemia. (See also Overview of Liver Disease.
The blood of butterflies and other insects is a colorless, clear liquid tasked only with delivering nutrients to tissues and carrying away waste.
If we're talking proportions, the majority of your blood—55 per cent to be exact—is actually kind of yellow. That's because, while red blood cells give blood its rosy colour, they're only one part of the picture. In fact, blood is made up of four components: red blood cells, white blood cells, platelets and plasma.
Your butterflies will expel a red liquid called meconium. This is a completely natural occurrence. Meconium is the leftover part of the caterpillar that was not needed to make the butterfly. This is stored in the intestine of the butterfly and expelled after the butterfly emerges.
Do caterpillars poop or pee?
The larval life stage - the caterpillar - does all of the eating, and caterpillars almost continually defecate. Interestingly, when there enough caterpillars eating in the same place, their defecation is audible.
Those yellowish or greenish liquid coming out of caterpillars is the blood (hemolymph) and protein present inside their body just like us. Our blood is red in colour and our body is formed of muscles and bones. Caterpillars don't have bones but they do have muscles.

This liquid is the leftover part of the caterpillar that was not needed to make the butterfly which is stored in the intestine of the butterfly and expelled after the butterfly emerges.
As a butterfly emerges, it will hold onto the paper in a vertical position while stretching its wings to full size. Don't be alarmed if you see a red liquid, which may look like blood, coming from the tail of the butterfly. This is called Meconium. It's a waste product left over from the butterfly's metamorphosis.
Caterpillars have a different type of blood from humans, known as haemolymph. It carries important nutrients and vitamins to the caterpillar's muscles and organs. It is likely therefore that it also carries the toxins the caterpillar has taken from its plant host, and therefore would also be poisonous.