Can light with certain colors/wavelengths be used in scorpion control?

 

Scorpions are a health problem in many areas, and especially in Brazil. As mentioned in a previous post, this problem is increasing due to medical important species' expansion into urban habitats. In a recent study, Marina Costa Rodrigues and co-workers tested behavioral reactions in the medical important scorpion Tityus serrulatus Lutz & Mello, 1922 (Buthidae) to light with different colors and wavelengths. 

The authors tested which colors or wavelengths that either attracted or repulsed the scorpions in a test arena. One main finding of the experiments was that the scorpions showed an avoidance to green light and violet light. More studies is necessary to see if lights with these colors can be used in scorpion control to either repel scorpions or attract them into traps.

Abstract:
Scorpions cause 150k+ accidents per year in Brazil. Control of their populations involves manual collection and pesticides. Here we tested if light could be used to attract or repel the yellow scorpion Tityus serrulatus, the main responsible for accidents in the country. Based on previous studies on scorpion´s physiological and behavioral reactions to light, we tested wavelengths that correspond to red, green and violet, controlling temperature, absolute irradiance and electromagnetic stimuli. We built a ring arena divided into 5 parts and had the individuals freely walking in the presence of a light/control. We released the scorpions either away from the LED to test attraction or close to the LED to test repellency. Results showed avoidance to green light, and violet light on a smaller portion, that could be due to wavelengths, since those correspond to primary and secondary response peaks of the animal photoreceptors, due to the absolute irradiance of lights or both. These two wavelengths, therefore, have potential for scorpion control and deserve further investigations.

Reference:
Rodrigues MC, Murayama GP, Moriyama LT, Ximenes N, de Souza L, Willemart RH. Light, camera, action: Behavioral responses of the yellow scorpion Tityus serrulatus to different lights. Behavioural processes. 2025;228:105207. [Subscription required for full text]

A study of the fluorescent sensilla on the scorpion aculeus (stinger)

 

It is well-known that scorpions fluorescence under UV light. This also apply for the scorpion's stinger (aculeus), but previous studies has shown a lack of fluorescence in the distal aculeus. Graeme Lowe has recently published an article where he used SEM imaging to study UV fluorescence in the acuelus of many species.

He observed numerous brightly fluorescent punctae in the non-fluorescent distal aculeus. These punctae were identified as aculear sensilla coeloconica (ASC). The ASC probably have a chemoreceptive function.

The author suggests that the ASC are playing an important role in the sensory coordination of telson function when the scorpions are trying to sting their prey and inject venom.

Abstract:
The aculeus of the scorpion telson was studied by UV fluorescence microscopy. Numerous brightly fluorescent punctae were observed on the non-fluorescent distal aculeus, including the tip region. The punctae were identified as aculear sensilla coeloconica (ASC), and were connected to fluorescent canals running through the cuticle. ASC were present in both sexes, and in adults and immatures as early as the second instar juvenile, but were absent from the first instar. The distal aculeus was found to be encased in a thick, non-fluorescent dark exocuticle (DX), covering an underlying thin, fluorescent hyaline exocuticle (HX). Fluorescent ASC were recorded from 183 species belonging to 97 genera in 19 families, encompassing all major scorpion lineages. The number of ASC in the tip region, the width of ASC canals, and the depth of the tip region, all exhibited positive correlation and allometric scaling with respect to carapace length. Higher tip densities of ASC occurred in some buthids, and in Scorpionoidea. The ASC are probably ubiquitous across the Order Scorpiones, playing an essential role in the sensory coordination of telson function during prey envenomation.

Reference:
Lowe G. Star-studded stingers: fluorescent sensilla on the scorpion aculeus (Arachnida: Scorpiones). Euscorpius. 2024;2024(402):1-39. [Open Access]

Shelter size and scent are factors that have an impact on shelter selection in females of two scorpion species

 

Shelter selection and shelters are important for the survival of most scorpions. Some scorpion dig their own burrow, others use naturally existing ones like cracks and crevices in rocks and stones, depressions under stones and burrows made by other animals.

Janina Hladik and co-workers have recently published a study investigation shelter selection (with focus on shelter size and scent) in females of Euscorpius italicus (Herbst, 1800) (Euscorpiidae) and Mesobuthus gibbosus (C.L. Koch, 1839) (Buthidae).

Females of both E. italicus and M. eupeus favor larger over smaller shelters, while they do not show clear preferences for conspecific scents. An impairment experiment showed that the scorpions could not detect size nor scent properly when either their pectines or pedipalps were impaired.

Abstract:
Shelter selection is an important task in an animal’s life. Concerning scorpions, little is known on the evaluation of potential shelters and the importance of chemosensation. To address these issues, we conducted a two-choice shelter test in rectangular open field arenas to identify properties rendering shelters attractive for female scorpions of the species E. italicus and M.  prey, aversive: rosemary oil). Contact with the shelters was video-recorded under red light for 13 h, including the whole night phase. Results revealed a preference for larger shelters, with conspecific scent having minor or no influence. Striking differences occurred with regard to prey and rosemary oil scents. Prey scent was more attractive to M. eupeus, while rosemary oil did not act as a repellent. E. italicus was not very attracted by prey scent, but was repelled by rosemary oil. These findings might reflect the different habitats, semi-arid vs. Mediterranean climates: prey and rosemary are scarce in the semi-arid climate (habitat of M. eupeus), whereas they are abundant in the Mediterranean climate (habitat of E. italicus). We carried out impairment experiments to identify the main sensory organs responsible for the above observations. These are the pectines and pedipalps which function as mechano- and chemosensors. Scorpions could not detect size nor scent properly when either their pectines or pedipalps were impaired.

Reference:
Hladik J, Bailer Y, Wolf H, Stemme T. Shelter selection in females of two scorpion species depends on shelter size and scent. J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2024. [Open Access]

Clustered setation on the pedipalps of buthid scorpions - morphology, taxonomic significance and a cleaning tool

 

The skin (exoskeleton) of scorpions has many different types of hairs (e.g. trichobothrias and setae). These have many functions, especially as sensory detectors of chemical substances and mechanical vibrations. For taxonomists they are also important morphological characters that can be used to identify taxa.

Trichobothriotaxy is already in great use in diagnosis  and description of many taxa (from species level to family level), but the usefulness of the setae (chaetotaxy) is less investigated. Graeme Lowe and Victoria Tang have now published a extensive study of chaetotaxy in scorpions with morphological descriptions of the different setation patterns in different taxa and the possible applications of these in taxonomy.

Interestingly, observations of Olivierus martensii (Karsch, 1879) (Buthidae) seem to indicate that this species uses setae clusters on pedipalps to brush the median ocelli (eyes) during sponge-bathing (cleaning behavior).

Abstract:
Chaetotaxy of the external pedipalp femur and distal ventral pedipalp movable finger was studied in 120 species, 69 genera and 17 families of scorpions. Setation was generally denser in the ‘Buthus’ group, a major arid-adapted buthid lineage distributed across Palearctic deserts. On the external femur, macrosetae formed a prominent cluster, the ‘distal external macrosetal cluster’ (DEMC); on the distal ventral movable finger they formed a dense patch, the ‘distal ventral macrosetal cluster’ (DVMC). In other buthids and non-buthids, the DEMC and DVMC were mostly absent, except in a few arid-adapted genera. Relative setation densities of DEMC and DVMC in different species depended strongly on size, being denser in larger species and sparser in smaller species, while absolute density varied only weakly with size (mean spacing of setae ~200 μm in DEMC, ~40 μm in DVMC). Ontogenetic variation followed similar trends. Multivariate morphometric analyses revealed taxonomic differences in setation patterns. The ‘Buthus’ group, other buthids, and non-buthids, were partially separable according to their spatial profiles of setation. In the ‘Buthus’ group, major genera were separable by spatial and density profiles of setation. In buthids, there were taxonomic differences in external femoral trichobothriotaxy. The ‘Buthus’ and Tityus’ groups were largely separable by proximodistal positioning of trichobothrium e1. Relative setation densities of DEMC and DVMC were positively correlated, in that species with dense DEMCs also tended to have dense DVMCs. In the buthid Olivierus martensii, DEMC and DVMC were observed to brush the median ocelli during sponge-bathing. In all examined buthids, the DEMC was located where it would contact the ipsilateral median ocellus during femoral articulation. Both DEMC and DVMC may assist in the ocular grooming of desert buthids, by removing sand and dust from surfaces of the median ocelli.

Reference:
Lowe G, Tang V. Clustered setation on the pedipalps of buthid scorpions (Scorpiones: Buthidae). Euscorpius. 2024(398):1-77. [Open Access]

Sensory structures in the aculeus part of the scorpion's tail

 

It is well known that scorpions can detect and use chemical cues and substrate vibrations thanks to chemosensitive hairs and other structures on the pectins and on part of the pedipalps. In a recent article, Melek Erdek and Ersen Yagmur describe and discuss potential sensory structures found in the scorpions' aculeus. Aculeus is the outer part of the telson where the stinger starts and it is covered with aculear peg sensilla and pore holes. 

Abstract:
The scorpion telson is composed of a bulbous shaped base with two venom glands and an aculeus with two venom channels that open to the exterior. The cuticular surface of the aculeus is covered with aculear peg sensilla and pore holes. These sensillar pegs are located on the aculeus surface of the telson and function as contact chemoreceptors. Data on aculear peg sensilla are presented from both parvorders, four families, 15 genera and 15 species of extant scorpions. Although all aculear peg sensilla have a similar structure in all species and sexes in terms of their general morphology, their location and frequency on the surface of the aculeus cuticle varies. The shape of these sensilla is similar in all species, and the distribution density on the cuticle surface differs from species to species. The single slit sensilla were observed at various intervals and numbers in the aculeus-bulb connection area of the telson.

Reference:
Erdek M, Yagmur EA. A comprehensive evaluation of the aculear sensory structures in scorpions (Arachnida: Scorpiones). Arthropoda Selecta. 2024;33(3):355-74. [Open Access]

Thanks to Ersen for sending me their article!

Using chemical cues to avoid intraguild predators and to find potential mates

 

It is well known that scorpions can detect and use chemical cues thanks to chemosensitive hairs on the pectins and on part of the pedipalps. Chemical cues can be used to discover and seek out conspecifics for mating, but also to avoid conspecifics or other scorpions that want to eat you (cannibalism is well documented in scorpions, often larger individuals preying on smaller and larger females may also kill and eat potential suitors).

Welton Dionisio-da-Silva and co-workers published earlier this summer a study of the use of chemical cues in the two Brazilian scorpions Bothriurus rochai Mello-Leitão, 1932 (Bothriuridae) and Jaguajir rochae (Borelli, 1910) (Buthidae). They tested the behavioral response to chemical cues from a heterospecific scorpion, and the response of male individuals (B. rochai and J. rochae) to chemical cues from conspecific females.

The study showed that smaller individuals avoided sites with the "smell" of larges individuals, whiles larger predators preferred the sites with the "smell" of smaller scorpions. In addition, males of both species trailed the chemical cues of females. 

According to the authors, this is the first evidence of a scorpion species detecting and hunting a heterospecific scorpion through chemical cues.

Abstract:
Chemical perception is essential among arthropods for mate recognition, prey search, and predator avoidance, especially for solitary predators which are often aggressive. Such mechanisms may be intensified in environments like the Caatinga, a seasonally dry tropical forest in Brazil, characterized by low habitat complexity and high seasonal variation. Thus, we investigated chemical perception between two scorpion species from this environment, involved in intraguild competition. Experiments assessed their response to chemical cues from prey, predators, and potential mates. We use Y-mazes to test the time spent by the scorpions between Y-arms with or without a given substrate-borne chemical cue (site preference) and the number of active individuals during trials (presence of activity). Scorpions’ activity was not influenced by chemical stimuli, although they clearly exhibit site preferences. The smaller predators avoided sites with the larger species’ chemical cues, while the larger predators preferred sites with the smaller species’ cues. Additionally, both species trailed female chemical cues. These findings suggest a dual-oriented arms race where prey and predator modulate their behaviour to avoid and hunt heterospecifics, respectively. This study provides the first evidence of a scorpion using chemical cues to detect a heterospecific scorpion and highlights the importance of this trait in arachnids.

References:
Dionisio-da-Silva W, Araujo Rocha-da-Silva KL, Veloso HMG, DaSilva MB. Hide and seek: chemical cues drive site preference among potential mates and intraguild competitors. Biological Journal of the Linnean Society. 2024:blae058. [Subscription required for full text]

Thanks to Welton Dionisio-da-Silva for sending me their article!

 

More on the function of the pectines in scorpion navigation

 

There have been a lot of research on the morphology and the functions of the pectines, which is a unique organ found only in scorpions (Solifigae has a similar organ called malleoli or racquet (or racket) organs). Most of the research so far have focused on the "taste function" (the detection of chemical cues), but it also seems that the pectines have a "feeling function" (having mechanosensory abilities). Overall, the pectines help scorpions find food, navigate, avoid predators and find mates.

Hannah Peeples and Douglas Gaffin recently published a study investigating the role of the peg sensilla on scorpion pectines for mechanosensory responses. This is a very technical paper, but as far as I can tell the main conclusion is that pectines use mechanosensory stimuli to navigate in its activity area, to find home to its shelter and to retrieve dropped insect prey.

Abstract:
Scorpions possess midventral touch/taste organs called pectines, which may be important for learning the nuances of the substrate during navigation as well as the detection of pheromones, spermatophores, and food. The pectines possess thousands of minute structures called peg sensilla that are responsive to both chemicals and mechanical deflection of the peg shaft. While much is known about the chemical responsiveness of the pegs, very little is known about their mechanosensory properties. Here we ask if the peg mechanosensory response is “all-or-nothing” or graded depending on the intensity of stimulation. We made electrophysiological recordings of neural activity from individual peg sensilla while deflecting the peg to elicit apparent mechanosensory responses. Our records show the presence of a rapid firing (.100 Hz), quickly adapting waveform that is indicative of a mechanoreceptor and appears to be independent of previously identified chemo-responsive cells. We tested mechanosensory response dynamics in two ways. The first test focused on a shorter-duration touch versus a longer-duration touch, while the second focused on a smaller deflection versus a larger deflection. Both pairs of stimulations (short vs long touch; small vs large touch) produced repeatable and statistically distinct responses in terms of spiking frequency. These results indicate the mechanosensory responses of peg sensilla are graded, which sheds light on the textural resolvability of the pectines and informs models of the type of information that scorpions obtain while assessing surfaces in their environment.

Reference:
Peeples HM, Gaffin DD. An assessment of the mechanosensory responses of peg sensilla on scorpion pectines. The Journal of Arachnology. 2024;52(1):1-8.

Thanks to Matt Simon for informing me about this article and for providing insight about the article!

Early Devonian scorpions also had pectines

 

Pectines are one of the body structures that are unique for scorpions. This comb-like structure is found on the underside of the opisthosoma of scorpions and is a sensory organ for detecting both chemical and mechanical stimuli. 

In a recent short note, Jason Dunlop and co-workers report about a cuticle fragment from a pectinal tooth from a Early Devonian scorpion. This fossil indicates that some scorpions had developed anatomically modern pectinal teeth at least 395 million years ago and that they probably had a similar function as the pectines in today's scorpions.

Abstract:
A cuticle fragment found in an Early Devonian (Emsian) macerate from the Strathpeffer–Struie outlier in the Northern Highlands of Scotland represents the isolated pectinal tooth of a scorpion. This remarkable find includes a distinctive field of small projections in rounded sockets consistent with the peg sensilla of extant scorpions. This is the oldest evidence for the presence of these characteristic sensory organs, which in modern scorpions play an important role in chemo- and mechanoreception. The fossil indicates that some scorpions had developed anatomically modern pectinal teeth at least 395 million years ago, suggesting that the pectines of these early scorpions played a similar role, physiologically and behaviorally, to those of living species.

Reference:
Dunlop JA, Wellman CH, Prendini L, Shear WA. A pectinal tooth with peg sensilla from an Early Devonian scorpion. The Journal of Arachnology. 2023;51(3):255-7, 3. [Subscription required for full text]

Thanks to Matt Simon for informing me about this article!

"Smelling" the enemy triggers anti-predator behavior in Ananteris mauryi

 

Fear is a powerful agent both in humans and animals and has an impact on behavior. For scorpions, the fear of being eaten by a predator (e.g. another scorpion) should promote behavior to avoid this happening. Matheus Feitosa and co--workers have recently publish an study on Ananteris mauryi Lourenço, 1982 (Buthidae) abilities to detect chemical cues left by its predator Tityus pusillus Pocock, 1893 (Buthidae) in the substrate when exploring new sites, and if this results in behavioral responses to avoid the risk of encounters and predation.

Their study confirms that Ananteris mauryi seems to be able to taste/smell its enemy Tityus pusillus because it tended to avoid substrates with chemical traces of T. pusillus. In addition, the taste/smell of its enemy also triggered anti-prdator behaviors like tail wagging.

Abstract:
Fear level and intraguild predation are factors that act together to directly influence animal behavior, population dynamics, and community structure. These factors trigger stress, which promotes behavioral, morphological, physiological, and demographic changes, especially in the prey. Some invertebrates, such as scorpions, are known to have a refined chemoreception system to perceive both prey and predators. Therefore, we investigated the ability of an intraguild prey, the scorpion Ananteris mauryi Lourenço, 1982, to detect chemical traces of its predator, the scorpion Tityus pusillus Pocock, 1893. Our goal was to verify whether A. mauryi exhibits antipredator behavior induced exclusively by chemical cues from its predator. Ananteris mauryi specimens were subjected to two experimental treatments: one with and one without traces of T. pusillus. The results showed that A. mauryi tended to avoid substrates with chemical traces of T. pusillus, confirming its capacity for chemical detection. As a result of this perception, changes in behavioral frequencies were triggered, generating an antipredator behavioral repertoire. These findings were supported by behavioral changes, such as tail wagging, which is performed exclusively by scorpions in the presence of a predator and at imminent risk of predation.

Reference:
Feitosa MLB, Dionisio-da-Silva W, Lira A, Teles-Pontes WJ. Fear as an enemy? Behavioral changes of Ananteris mauryi Lourenço, 1982 (Scorpiones: Buthidae) are triggered by chemical cues from an intraguild predator. Can J Zool. 2022;100:488-93 [Subscription required for full text]

Thanks to Andre Lira for sending me his articles!

How does Paruroctonus utahensis find its way home

 

Finding the way home is an important skill for burrowing scorpions like Paruroctonus utahensis (Williams, 1968) (Vaejovidae). There have been some indications that scorpions use a view-based navigational process termed "Navigation by Scene Familiarity", which has been seen in bees and ants. Douglas Gaffin and co-workers have recently published a study where they investigate if scorpions may be guided by tastes and touches acquired via their mid-ventral pectines, instead of or in addition to vision.

The authors have named this form of homing "The Navigation by Chemotextural Familiarity Hypothesis (NCFH)". In their study they find evidence of learning walks during burrowing in Paruroctonus utahensis and they conclude that these putative learning walks, together with recently reported path integration in scorpions, may provide the crucial home-directed information requisite for NCFH. 

Abstract:
The navigation by chemo-textural familiarity hypothesis (NCFH) suggests that scorpions use their midventral pectines to gather
chemical and textural information near their burrows and use this information as they subsequently return home. For NCFH to be viable, animals must somehow acquire home-directed ‘tastes’ of the substrate, such as through path integration (PI) and/or learning walks. We conducted laboratory behavioral trials using desert grassland scorpions (Paruroctonus utahensis). Animals reliably formed burrows in small mounds of sand we provided in the middle of circular, sandlined behavioral arenas. We processed overnight infrared video recordings with a MATLAB script that tracked animal movements at 1–2 s intervals. In all, we analyzed the movements of 23 animals, representing nearly 1500 h of video recording. We found that once animals established their home burrows, they immediately made one to several short, looping excursions away from and back to their burrows before walking greater distances. We also observed similar excursions when animals made burrows in level sand in the middle of the arena (i.e. no mound provided). These putative learning walks, together with recently reported PI in scorpions, may provide the crucial home-directed information requisite for NCFH.

Reference:
Gaffin DD, Munoz MG, Hoefnagels MH. Evidence of learning walks related to scorpion home burrow navigation. J Exp Biol. 2022;225:jeb243947. [Open Access]

Are trichobothria really necessary in scorpion prey capture?

It is a well known fact that the scorpion trichobothria on their pedipalps are very important in how the scorpions sense their environment. They use these small hairs to detect vibrations in the air and in the substrate, but direct behavioral studies on the use of trichobothria and natural prey capture are scarce.

Gabriel Pimenta Murayama and Rodrigo Hirata Willemart have recently published an interresting  study where they tested if the trichobothria are important in prey capture in Tityus serrulatus Lutz & Mello, 1922 (Buthidae). I must admit I assumed the answer was yes, but surprisingly their results suggested that the trichobothria of T. serrulatus was not essential to capture terrestrial prey.

It is important to remember that scorpions do have other types of sensory hairs (sensilla) on different parts of their body and these may play a role in detecting prey in the scorpions vicinity.

Abstract:
Many arachnids rely on substrate-borne vibrations and air displacement to detect prey. Air-flow stimuli may be detected by long setae called trichobothria, which occur on scorpion pedipalps, but seldom have their functions been addressed in these animals. We tested the hypothesis that trichobothria on scorpion pedipalps are important for capturing terrestrial prey in the scorpion Tityus serrulatus. We predicted that scorpions with trichobothria experimentally removed would be less successful in capturing terrestrial prey than the control groups. We also predicted that scorpions without trichobothria would have a higher number of capture attempts, that the latency to detect prey and to the first capture attempts would be higher, and the number of times that scorpions oriented their body towards the prey would be lower. We used an experimental subject and a cricket in an arena with a paper sheet as substrate. We did not find differences in the measured variables between the groups. Other sensory organs, such as basitarsal compound slit sensilla and tarsal hairs would enable scorpions to detect prey by substrate-borne vibrations, compensating for the lack of trichobothria. Our results suggest that the trichobothria of T. serrulatus may not be essential to capture terrestrial prey.

Reference:
Murayama GP, Willemart RH. Are trichobothria used in terrestrial prey capture by the yellow scorpion Tityus serrulatus Lutz & Mello, 1922 (Buthidae)? Arachnology. 2019;18(3):287-90.

Scorpions can actually smell their enemies

It has been known for a long time that scorpions can smell (detect chemical substances) with their pectines and pedipalpal fingers. Zia Nisani and Raul Curiel report for the first time that scorpions are also able to smell the presence of potential predators. In a research trial they were able to show that individuals of Hadrurus arizonensis (Ewing, 1928) (Caraboctonidae) changed behavior in the presence of odor from a potential predator. The advantages of such an ability is of course quite obvious.

Abstract:
Sensory ecology studies show that reception and utilization of information from the environment is a crucial life process. Scorpions possess a weapon that can be used against predators, but it remains unknown whether scorpions’ decision to use it is influenced by chemical cues from predators. We investigated the influence of predators’ odors on stinging behavior of Hadrurus arizonensis (Ewing, 1928) by stimulating them to sting under two conditions: in the presence of an odor from a potential rodent predator (Rattus norvegicus) and in the absence of such an odor. It took fewer probes to elicit a response when predator scent was present, and it resulted in more wet stings than the non-scented treatments. Finally, the smaller scorpions were more reactive than the larger ones. The variances in stinging behavior suggest that the detection of predator odors by H. arizonensis elevates its response in potentially threatening circumstances.

Reference:
Nisani Z, Curiel R. Antipredator responses of Hadrurus arizonensis (Scorpiones: Caraboctonidae) to chemosensory cue from a mammalian predator. J Arachnol. 2019;47:389-91. [Open Access]

A major study of the scorpions' lateral eyes

Scorpions have two types of visual organs (usually called eyes): the median and the lateral eyes. Most scorpions have a single pair of median eyes (except for a few troglomorphic species), but the number of pairs of lateral eyes varies very much between the different scorpion taxa and even within some species.

Loria and Prendini have now published a comparative study of variation in the lateral eyes of scorpions based on examinations of a broad range of taxa. The main conclusions of the study can be found in the abstract below.

Abstract:
Scorpions possess two types of visual organs, the median and lateral eyes. Both eyes consist of simple ocelli with biconvex lenses that differ in structure and function. There is little variation in the number of median ocelli across the order. Except for a few troglomorphic species in which the median ocelli are absent, all scorpions possess a single pair. In contrast, the number of pairs of lateral ocelli varies from zero to five across Scorpiones and may vary within species. No attempt has been made to homologize lateral ocelli across the order, and their utility in scorpion systematics has been questioned, due to the variation in number. A recent study examined the number of lateral ocelli among various Asian Buthidae C.L. Koch, 1837 and proposed a ‘‘five-eye model’’ for the family. This model has not been examined more broadly within Buthidae, however, nor compared with the patterns of variation observed among other scorpion families. An eyespot, referred to as an accessory lateral eye, situated ventral or posteroventral to the lateral ocelli, has also been reported in some scorpions. Analysis of its structure suggests it serves a nonvisual function. We present the first comparative study of variation in the lateral ocelli across the order Scorpiones, based on examination of a broad range of exemplar species, representing all families, 160 genera (78%), 196 species (9%), and up to 12 individuals per species. We propose a six-ocellus model for Recent scorpions with four accessory ocelli observed in various taxa, homologize the individual ocelli, and correct erroneous counts in the recent literature. We also investigate the presence of the eyespot across scorpions and discover that it is more widespread than previously recognized. Future work should investigate the genetic and developmental mechanisms underlying the formation of the lateral ocelli to test the hypotheses proposed here.

Reference:
Loria SF, Prendini L. Homology of the Lateral Eyes of Scorpiones: A Six-Ocellus Model. PLoS One. 2014;9(12):e112913. [Free full text]

Thanks to Matt Simon for informing me about this article!