Do Bees Have Kidneys?
Do bees have kidneys? An interesting question. In order to answer the question, we must first understand what kidneys are, what they do, and where they are found.
What are kidneys and do bees have them?
Kidneys are organs found in vertebrates. In vertebrates, they fulfil a number of roles:
- Kidneys are responsible for the excretion of a number of waste products from the body by creating urine – this is done in the main functional unit of the kidney, the nephron;
- Kidneys secrete some hormones – most notably erythropoietin (which stimulates production of red blood cells in response to lower body oxygen levels) and calcitriol (which is the active form of vitamin D and promotes absorption of calcium in the intestine);
- Kidneys play a critical role in blood pressure management via the ‘renin-angiotensin’ system;
- Kidneys help maintain acid-base balance in the body;
- Kidneys
are part of the system that maintains hydration and water-salt balance.
However, can we say that bees have kidneys?
Bees are insect invertebrates, and do not have kidneys. However, they have an internal system which performs the role of kidneys.
This system is called the Malpighian tubule system. This system fulfils both excretory and water regulatory functions for bees.
What is the Malpighian system, and where is it found?
You may have seen the page on this website about bee hearts.
If you have, you will know that, like all insects, bees have a body cavity containing a substance known as hemolymph, within which are their organs.
The Malpighian system is a system of highly convoluted tubules that is found within the abdomen of bees. The tubules are bathed in the hemolymph and connect into the bees’ alimentary canal.
How does the Malpighian system work in bees?
Waste products and electrolytes (urea, amino acids, potassium, sodium) pass from the hemolymph into the tubules along with water.
This ‘pre-urine’ passes down the tubules into the alimentary canal, where it merges with digested food. Uric acid precipitates out, while potassium and sodium are reabsorbed along with water.
The uric acid continues along the alimentary canal and is then excreted in the faeces (bee poop). So, the uric acid excretion is a similar function to the passing of urine in mammals, while the passage of electrolytes and water into the tubules together with their appropriate reabsorption later is the bees’ water balance function.
How many Malpighian tubules does honey bee have?
In honey bee larvae, the number of tubules is 4, whereas in adults there are 100 tubules1.
Do all bee species have the same number of Malpighian tubules?
The simple answer to this question is – no!
It has been observed (for example, in Barbosa-Costa et al1 that not only are the number of Malpighian tubules in larvae and adult bees is variable, it also varies between species.
Barbosa-Costa et al found that in stingless bee species, the number of Malpighian tubules varies considerably: some groups have four to eight tubules in the larvae and seventy to ninety in adults; while other groups have four tubules in larvae and only twenty to forty tubules in adult bees.
Reference:
1. Barbosa-Costa, K., Kerr, W.E. & Carvalho-Zilse, G.A. Number of Malpighian Tubules in Larvae and Adults of Stingless Bees (Hymenoptera: Apidae) from Amazonia. Neotrop Entomol 41, 42–45 (2012). https://doi.org/10.1007/s13744-011-0017-5
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