Bees are fascinating creatures that play a vital role in pollinating plants and producing honey. Given their small size, many people wonder if bees even have blood or a circulatory system. In this article, we’ll explore the anatomy of bees to find out if they have blood and how their circulatory system works.
Do Bees Have Blood?
Yes, bees do have blood and a circulatory system. However, there are some key differences between insect blood and the blood found in vertebrates like humans:
- Insect blood is called hemolymph.
- It does not contain red blood cells or hemoglobin and is not used to transport oxygen.
- Hemolymph circulates in an open system rather than a closed system of veins and arteries.
- It contains plasma and hemocytes but does not clot.
So in short, bees have a liquid circulating fluid called hemolymph that functions like blood, but lacks some key components found in vertebrate blood.
Anatomy of a Bee’s Circulatory System
A bee has an open circulatory system that is much simpler than the closed circulatory system found in humans and other vertebrates. Here are the key anatomical structures involved in a bee’s circulation:
- Heart: Bees have a long tube-like heart that runs the length of their body. It has segments and openings for hemolymph to enter.
- Hemocoel: This cavity fills most of the bee’s body and contains the hemolymph.
- Ostia: Valve openings along the heart that allow hemolymph in.
- Arteries: Bees do not have distinct arteries. The heart pumps hemolymph into the main body cavity.
- Veins: Bees lack veins to return blood. Hemolymph circulates passively around the body.
- Hemocytes: Cellular elements in the hemolymph that function like white blood cells.
Diagram of a Bee’s Circulatory System
Here is a diagram of the simple circulatory system found in bees:
Image source: Mariana Ruiz Villareal
As you can see, it is an open system with the hemolymph free flowing through the hemocoel cavity and not contained in blood vessels like veins and arteries.
How Does a Bee’s Circulatory System Work?
A bee’s circulatory system functions to distribute nutrients, hormones, and other substances around the body. Here is how circulation works:
- Hemolymph fills the hemocoel cavity and surrounds the organs.
- Segmented heart pumps hemolymph from rear to front.
- As hemolymph passes through the heart, ostia allow entry into heart tubules.
- Hemolymph exits heart into hemocoel cavity again.
- Free flow and pressure gradients circulate hemolymph around body.
- Wastes diffuse back into hemolymph from tissues.
- Hemocytes phagocytize bacteria and other pathogens.
This form of circulation allows for:
- Transport of nutrients from digestive system.
- Distribution of hormones from endocrine glands.
- Removal of metabolic waste like lactic acid.
- Immune defense via circulating hemocytes.
In summary, the bee heart pumps hemolymph through the hemocoel cavity to deliver nutrients and other essential substances throughout the body.
What is Bee Hemolymph Made of?
Bee hemolymph contains plasma and hemocytes but lacks the specialized carrier cells found in vertebrate blood. Here are the main components:
| Component | Description |
|---|---|
| Plasma | Fluid portion that transports metabolites and hormones. |
| Hemocytes | Various cell types that phagocytize invaders. |
| Proteins | Transport proteins, clotting factors, antimicrobial peptides. |
| Sugars | Mainly trehalose which stores carbohydrates. |
| Salts | Ions like Na+, K+, Ca2+, Mg2+. |
| Water | Up to 70% of hemolymph volume. |
The plasma portion of hemolymph has a composition somewhat similar to blood plasma. But specialized cells like red blood cells and antibodies are not present since insects lack an adaptive immune system.
Hemolymph Hemocyte Cells
There are 5-6 types of hemocytes, or blood cells, found in bee hemolymph:
- Prohemocytes – Immature cells that can differentiate into other cell types.
- Plasmatocytes – Most abundant cells that phagocytize invaders.
- Granulocytes – Contain prophenoloxidase enzymes involved in clotting.
- Oenocytoids – Produce phenoloxidase enzymes.
- Spherule cells – Function not well understood.
- Coagulocytes – Help hemolymph coagulate.
These hemocyte cells give bee hemolymph some immune function and clotting ability. However, hemolymph does not contain an adaptive immune system or deliver oxygen like vertebrate blood.
Do Bees Lose Hemolymph When They Sting?
When a honey bee stings, it is effectively committing suicide because its stinger becomes lodged in the victim’s skin. When the bee tries to pull away, it rips out part of its own abdomen including digestive and circulatory organs. This massive abdominal wound causes extensive hemolymph loss and death usually follows within minutes to hours.
Bee Stinger Anatomy
Here is what happens inside a bee’s abdomen when it stings:
- The stinger is modified from reproductive structures (ovipositor).
- It contains a venom gland and venom sac.
- Muscles pump venom through a canal and out the stinger tip.
- Barbs on the stinger anchor it in victim’s skin.
- When bee tries to pull away, it rips out sting apparatus and nearby organs.
This massive abdominal wound damages the digestive tract, ruptures the honey stomach, and causes catastrophic hemolymph loss. Without the ability to circulate hemolymph, the bee dies shortly after stinging.
Do Other Insects Have Hemolymph?
Yes, hemolymph is found in all arthropods – the phylum that contains insects and crustaceans. Any creature with an exoskeleton rather than an internal vertebrate skeleton relies on hemolymph for internal circulation. This includes:
- All insect groups like flies, ants, beetles, butterflies, etc.
- Spiders, scorpions, ticks, and mites.
- Centipedes and millipedes.
- Crustaceans like lobsters, crabs, shrimp.
The exact composition of hemolymph varies somewhat between species. But in general, arthropod hemolymph contains plasma, hemocytes, sugars, salts, and proteins. It functions to deliver nutrients and hormones but does not transport oxygen or utilize specialized carrier cells like vertebrate blood.
Major Differences Between Insect Hemolymph and Vertebrate Blood
| Hemolymph | Vertebrate Blood |
|---|---|
| – Does not contain hemoglobin | – Rich in hemoglobin within RBCs |
| – Does not transport oxygen | – Transports oxygen via RBCs |
| – Circulates in open system | – Contained in closed system of veins & arteries |
| – No distinct lungs or breathing | – Oxygenates via lungs or gills |
| – No white/red blood cell distinction | – Many specialized blood cell types |
In summary, the primary distinctions are the lack of oxygen transport and specialized blood cells like erythrocytes and leukocytes in insect hemolymph.
Conclusion
To summarize, bees do have a circulating fluid called hemolymph that is analogous to blood. However, hemolymph has different properties and composition compared to vertebrate blood. The main points are:
- Bees have an open circulatory system with a segmented heart.
- Hemolymph contains plasma, hemocytes, sugars, and salts.
- It circulates nutrients and hormones but does not carry oxygen.
- Hemolymph loss is what kills a bee after stinging.
- All insects and arthropods rely on hemolymph for circulation.
So in short – yes bees do have “blood”, but it’s a different substance than the blood found in vertebrates. This circulatory fluid called hemolymph is essential for transporting nutrients and immune cells throughout a bee’s body to keep it alive.