Review of diel rhythmic activities in physiological functions of scorpions


Correspondence: Michael R. Warburg, Department of Biology, Technion-Israel Institute of Technology, Haifa, 32 000, Israel.



In this study I review the subject of biological rhythms in scorpions. This will include only some of the diel rhythmic endogenous physiological functions and not the locomotory rhythmicity, which will be dealt separately. Most studies reported here were conducted on 13 scorpion species that were studied in 39 different studies. Most of these (66.7%) were studies on a single species (Heterometrus fulvipes). Being a scorpionid, it sits and waits near its burrow not being very active, especially the females. The fact that experimenting was carried out irrespective of species diversity, gender, ecological or physiological conditions, and was usually done on animals kept in captivity for some time before the experimenting had started, is a major drawback to this kind of study. Although the main conclusion appears to be that enzymes reached their peak activity at 20.00 h, there are some exceptions showing otherwise that need further study in order to explain them.


In this study I review diel rhythmic activity seen in some physiological (biochemical) functions in scorpions. I have discussed this subject only briefly in a previous review (Warburg & Polis 1990). The present review would not include a discussion of the subjects of “zeitgebers” or entrainments, or of locomotory rhythmicity. These will be discussed separately (Warburg, unpubl. data, 2013). Most studies reported here were conducted on 13 scorpion species in 39 studies (Table 1). Most of them (26) were conducted on a single species, Heterometrus fulvipes C L Koch, 1838.

Table 1. Scorpion species used in studies on physiological rhythms
Androctonus australis (Linnaeus, 1758)
Goyffon M. et al. (1975); Fleissner & Heinrichs (1982); Fleissner & Fleissner (1986)
Androconus mauretanicus (Pocock, 1902)
Goyffon M et al. (1975)
Buthus europaeus (Linnaeus, 1758)
Corteggi & Serfaty (1939)
Buthus occitanus (Amoreux, 1789)
Goyffon M et al. 1975
Euscorpius italicus (Herbst, 1800)
Dresco-Derouet (1961)
Euscorpius carpathicus Linnaeus, 1767
Dresco-Derouet (1961)
Euscorpius flavicaudis (DeGeer, 1778)
Carricaburu & Munoz-Cuevas (1986a)
Hadrurus arizonensis (Ewing, 1928)
Ziganow (1976)
Didymocentrus lesuerii Kraepelin, 1905
Carricaburu & Munoz-Cuevas (1986b, 1987)
Carricaburu et al. (1982)
Heterometrus fulvipes (C L Koch, 1838)
Reddy & Padmanabha Naidu (1977a,b)
Reddy et al. (1978)
Vasantha et al. (1977)
Chengal Raju et al. (1973)
Chengal Raju et al. (1976)
Devarajulu Naidu (1969)
Devarajulu Naidu & Padmanabha Naidu (1976)
Devarajulu Naidu & Padmanabha Naidu (1977)
Jayaram & Padmanabha Naidu (1979)
Jayaram et al. (1978)
Masthanaiah et al. (1977)
Masthanaiah et al. (1978)
Jayaram & Padmanabha Naidu (1980)
Masthanaiah et al. (1979)
Rao & Govidappa (1967)
Rao & Habibulla (1973)
Reddy & Naidu (1977a,b)
Raghavaiah et al. 1978a,b
Reddy et al. (1978)
Uthaman & Srinavasa Reddy (1979)
Uthaman & Srinavasa Reddy (1985)
Venkatachari & Muralikrishna Dass (1968)
Venkatachari & Naidu (1969)
Venkatachari (1971)
Venkateswara Rao & Govindappa 1967
Heterometrus swammerdami (E Simon, 1872)
Habibula (1971)
Rao & Habibulla (1973)
Heterometrus maurus Thorell, 1876
Corteggiani & Serfaty (1939)
Pandinus imperator (C L Koch, 1841)
Goyffon et al. 1975


Photic behavior


The photoreceptors are of great importance for entrainment of circadian rhythms in scorpions (Ramakrishna & Pampathi Rao 1971). This major subject will be dealt separately.

Auditory behavior

This aspect of behavioral rhythmicity was very little studied in scorpions. Nevertheless, it is of great importance for the animals once active outside their shelter (Ramakrishna & Pampathi Rao 1971).

Diel endogenous rhythm

Neurosecretory activity

Neurosecretory activity in scorpions was studied by Habibulla (1971), who studying Heterometrus swammerdami (E Simon, 1872), found that the brain contains in the cephalothoracic nerve mass lipoproteins as well as alanine, arginine and aspartic and glutamic acids. Rao and Habibulla (1973) correlated diurnal activity of neurosecretory cells (NSC) in the lateral cells of groups numbers 3, 4 and 5, with the circadian type of locomotory activity phase which took place between 18.00 h to about 24.00 h. Heinrichs and Fleissner (1987) found the efferent neurosecretory fibers supply the median eyes with circadian information.

Vasantha et al. (1977) found that the neurohormones modulate enzyme activity. Enzyme activity in the ventral nerve chord shows diurnal rhythmicity maximum at 16.00 h and at 04.00 h. Similar diurnal rhythmicity was seen in the spontaneous electrical activity of the central nervous system.

Uthaman and Srinavasa Reddy (1980) studying Heterometrus fulvipes found that neural factors regulate oxygen consumption rhythm in isolated hepatopancreatic tissue of the scorpion. In a later study Uthaman and Srinavasa Reddy (1985) found the rhythmic changes in the activity of neurosecretory cells of the scorpion to be bimodal, peaking both at 12.00 h and at 24.00 h. These two peaks lie 6 h in advance of the locomotory peaks. Similarly, Fleissner (1983) studying the buthid Androctonus australis (Linnaeus, 1758) described the pacemaker in central nervous system.

Carricaburu and Muñoz-Cuevas (1986a,b) described the periodic electrical waves, observing them only at night when they mark the activity of the sub-esophageal pacemaker. The signal travels through the optic nerve by nervous rather than hormonal stimulus. Therefore, the visual pacemaker is located in the supra-esophageal ganglion. The second pacemaker lies in the sub-esophageal ganglion and sends axons to the legs (Habibulla 1971). Later Habibulla (2004) found the maximal brain serotonin to occurs at 24.00 h and minimum at 04.00 h.

Diel enzyme activity effect on circulation

Heart beat

Devarajulu Naidu (1969) studying H. fulvipes found rhythmic activity in the heartbeat, showing that it originated in the seventh ganglion with the heartbeat commencing in the posterior part of the heart.

Devarajulu Naidu and Padmanabha Naidu (1976) described the diurnal activity in the heartbeat of the scorpion, which peaks at 20.00 h (heartbeat of 65 beats/min), and is lowest at 08.00 h (heartbeat of 45 beats/min). Moreover, each of the spontaneous volleys of bursts of the cardiac ganglion corresponded to contraction of the heart muscle. Inhibitory effect of cholinesterase was shown to follow a circadian rhythm with maximum activity of the enzyme at 20.00 h and minimum at 08.00 h. In 1974 they suggested that the heartbeat is neurogenic as evidenced by the presence of a cardiac ganglion with its spontaneous rhythmic burst activity.

Heartbeat and glycogen

Jayaram et al. (1978) described the circadian rhythmicity in phosphorylase activity and glycogen content in the heart muscle of the scorpion peaking at 20.00 h and low at 08.00 h Jayaram and Padmanabha Naidu (1979) found that females had a significant lower heartbeat and higher carbohydrate levels than males, which showed higher phosphorylase, succinate (SDH), lactate (LDH) and dehydrogenases activities.

Heart beat and cholinesterase

Cholinesterase (ChE) is a family of enzymes that catalyze the hydrolysis of choline esters chiefly at nerve terminals, where it hydrolyzes and inactivates acetylcholine into choline and acetic acid. This is a reaction necessary to allow a cholinergic neuron to return to its resting state after activation. It is also called acetylcholinesterase (ACh) of the neurotransmitter.

Venkatachari and Muralikrishna Dass (1968) described diel rhythm of ChE activity peaking about 16.00 h with lowest peak at 04.00 h. ChE peaked at the maximum rate of heartbeat (Naidu 1969, Venkatachari & Naidu 1969). Venkatachari (1971) analyzed the spontaneous electrical activity in various regions of the nerve cord and peripheral nerve. They demonstrated a rhythmic activity pattern with a minimum at 04.00 h and a maximum at 16.00 h. These peaks occur at a later time than those of the ventral cord; a biochemical basis for diurnal rhythm is the activity of ChE. Corteggi & Serfaty (1939) suggested the neurohumoral function of acetylcholine (ACh) in Buthus europaeues (Linnaeus 1758), and Heterometrus maurus (Thorell, 1876) seems to control diurnal rhythms in the heartbeat. ChE and glucose content of heart muscle activity have shown a rhythmic activity (Devarajulu Naidu & Padmanabhanaidu 1974). Devarajulu Naidu and Padmanabha Naidu (1977) showed that concentrations of ACh type or cardio-accelerating substance was higher in the sub-esophageal (41.3 μg/g wet wt) and least in the meso-somatic region (14.2 μg/g).

Reddy Chandra Sekara et al. (1978) described the rhythmicity of muscular activity in the scorpion's appendages with ACh activity peaking at 20.00 h and was minimal at 08.00 h.

Carricaburu et al. (1982) found that the inhibitor Carabryl, an anticholinesteraseic drug, increased the amplitude and frequency of the spontaneous electrical activity of the scorpion nervous system.


A dehydrogenase (DHO) is an enzyme that oxidizes a substrate by a reduction reaction. This enzyme catalyzes the removal of hydrogen from a substrate, and the transfer of the hydrogen to an acceptor in an oxidation-reduction reaction.

Rao and Govidappa (1967) found conspicuous differences in the dehydrogenase activity during the day and night. Increased dehydrogenase activity at night correlates with increased locomotory activity of the scorpion. Both dehydrogenases and esterases exhibited diurnal rhythmic activity (Reddy Chandra Sekara & Naidu, 1977a). DHO (lactate, succinate, malate) activity in leg, pedipalpal and heart muscles peaked at night (Venkateswara Rao & Govidappa 1967).

Masthanaiah et al. (1977) described the rhythmic variations in the isocitrate dehydrogenase (an enzyme vital to the citric acid cycle) activity in the scorpion muscle and hepatopancreatic tissues. It peaked at night at 20.00 h and was lowest at 08.00 h.


Phosphorylases are enzymes that catalyze the addition of a phosphate group from an inorganic phosphate (phosphate + hydrogen) to an acceptor. Jayaram and Padmanabha Naidu (1979) found that females had significantly lower heartbeat and higher carbohydrate levels than males, which had higher phosphorylases, SDH, LDH and DHO activities. Chengal Raju et al. (1976) have shown phosphorylase activity peaked at 20.00 h and was lowest at 08.00 h. Jayaram et al. (1978) described the circadian rhythmicity in phosphorylase activity and glycogen content in the heart muscle of the scorpion found peaking at 20.00 h and was lowest at 08.00 h. Jayaram and Padmanabha Naidu (1979) found significantly lower heartbeat and higher carbohydrate levels in females. However, males had higher phosphorylases, SDH, LDH and dehydrogenases activities. Likewise, rhythmic activity has been described in levels of both blood glucose and heart muscles as well as in levels of hepatopancreatic glycogen (Chengal Raju et al. 1973). The circadian rhythms in blood glucose peaked at 20.00 h, becoming lowest between 04.00 and 08.00 h, whereas liver glycogen peaked at 08.00 h and was lowest at 20.00 h. Chengal Raju et al. (1978) found hemolymph glucose and hepatopancreatic glycogen differ between genders: the first is 25.6% higher and the second 22.8% lower in males than females. Phosphorylases activity was higher in males.


Jayaram and Padmanabha Naidu (1980) found that accelerated heartbeat caused glucose depletion, whereas phosphorylase increased with increasing heart beat.

Masthanaiah et al. (1978) found a diel rhythmic activity of lipase in the scorpion peaking at 20.00 h with a minimum at 8.00AM. Lipase is a hydrolyzing enzyme that hydrolyzes esters of high molecular weight into fatty acids and glycerol.

Diurnal rhythmic activity of alkaline and acid phosphatase peaked at night at 20.00 h with minimum at 08.00 h (Reddy Chandra Sekara & Naidu, 1977b). They found activity peaked in all three tissues (heart, muscle and nerves).

Enzyme activity and its effect on respiration

This was studied in Euscorpius italicus (Herbst, 1800) and E. carpathicus (Linnaeus, 1767) by Dresco-Derouet (1961), who found a peak at 20.00 h.

The oxygen consumption of isolated muscles was studied by Uthaman and Srinivasa Reddy (1979). They found two bimodal peaks at 08.00 h and at 20.00 h.


There are several main problems with the research done so far on the physiological aspects of circadian rhythm. These are:

  1. The research was carried out irrespective of species diversity, gender, ecological or physiological conditions, and was usually done on animals kept in captivity for some time before the experimenting had started.
  2. Several experiments were conducted on single animals kept in the arena others used for groups (of 10 or 20 animals) (Ramakrishna & Pampathi Rao 1971). Thus, metabolism of the animal may be affected by both ambient conditions or by internal factors such as oogenesis, vitellogenesis and embryogenesis, each of which has an effect on metabolism of the female scorpion (Warburg 2012).
  3. Moreover, most experiments (66.7%) were conducted largely on a single scorpionid species H. fulvipes. Being a scorpionid, it by nature sits and waits for its prey; thus it does not show much activity (especially females). Such inactivity affects metabolic processes and is therefore not a good indicator of any cyclic events in the body.

One major problem is the fact that there are various reports on an unexplained delay in neurosecretory activity peaking at 18.00 h to about 24.00 h (Rao & Habibula 1973), or showing a bimodal activity peaking at either 16.00 h or 04.00 h (Vasantha et al. 1977), or at 12.00 h and at 24.00 h (Uthaman & Srinivasa Reddy 1985; Habibulla 2004). Similarly, cholinesterase activity peaks about 16.00 h (Venkatachari & Muralikrishna Dass 1968; Venkatachari 1971). All these need further studies in order to be explain them.

In conclusion, it is important to study enzymatic parameters in more than a single animal species and more than single individuals. It would be best to know the age, gender and gonad situation of the animals. It is essential to know whether the animals had food available to them ad libitum. In addition, it is essential to allow for behavioral aspects affecting physiology such as burrowing activity, nocturnal activity and mating behavior.