Coral cuello negro
Micrurus obscurus

Only a single case of mild envenomation by a captive Micrurus obscurus specimen has been reported to date [1]. Reported symptoms include persistent, severe generalized pain in the joints, bones, and the tooth sockets [1]. The symptoms associated with more severe grades of envenomation for M. obscurus remain unknown because no snakebite accidents caused by this species have been recorded in Colombia’s National Public Health Surveillance System (SIVIGILA, Spanish acronym). 

The venom of M. obscurus is predominantly neurotoxic; the symptoms of envenomation by M. obscurus are, thus, likely to be like those that have been reported for envenomation by coralsnakes with venom having similar properties [2–4]. Local symptoms that are often observed following mild envenomation by coralsnakes include reddening of the skin (erythema), swelling, and muscle pain (myalgia) [5,6]. Local symptoms associated with moderate envenomation include severe reddening of the skin (perilesional erythema), as well as burning and aching (dysesthesia) [5,6]. Various systemic symptoms that can be observed following moderate envenomation include abnormal tingling sensation (paresthesia), drooping of the upper eyelid (palpebral ptosis), compromised ability to  speak, due to muscle weakness (dysarthria), and altered taste (dysgeusia) [5,6]. Following severe envenomation, patients can experience flaccid paralysis within 30 minutes of the bite, along with the production of excessive amounts of saliva (sialorrhea), paralysis of the neck muscles (“broken neck sign”), shortness of breath (dypsnea), and paralysis of the breathing muscles leading to ventilatory failure [5–7].​

Medical treatment is essential for ensuring patient safety following envenomation by Micrurus obscurus due to the rapidity with which serious symptoms can arise. After a bite by M. obscurus, the bitten limb should be immobilized, and the patient should be taken to a hospital as quickly as possible [8]. The application of ice, medicinal plants, or any other treatments to the site of the bite are not recommended given that many of these treatments have not been demonstrated as clinically effective and, more importantly, they can delay arrival to a hospital. 

The number of antivenom vials that should be administered depends on the grade of envenomation (mild, moderate, or severe) and the geographical origin of the accident should be considered [8]. In cases occurring in the Amazon or Orinoquia regions, 10 vials of INS antivenom may be required, [6]. These recommended dosages are the same for both children and adults, and the administration of antivenom should be performed exclusively by qualified medical practitioners [9]. 

In Colombia, M. obscurus occurs in the Amazon, Orinoquia, and the foothills of the Andes up to 620 m [10,13]. It has been documented in the following departments: Amazonas, Caquetá, Guaviare, Meta, Putumayo, Vaupés, and Vichada. The potential area of the distribution of M. obscurus in Colombia is 580328,79 km2 (Figure 1).

Figure 1. Geographic distribution of Micrurus obscurus in Colombia and its habitat suitability model. Based on bioclimatic variables, the habitat suitability model predicts the species' potential distribution in Colombia, identifying zones with suitable or unsuitable environmental conditions for its occurrence across the country. Values close to 1 indicate optimal environmental conditions (high probability of presence), while values close to 0 indicate unsuitable conditions (absence likely).​

Uncommon. This snake can occur in diverse habitats, including tropical rainforest, secondary growth, savanna, and gallery forest [10,11,14–16]. It has also been found in pastures and near human habitations, but it is most common in humid forested areas [10,15,17,18]. Both diurnal and nocturnal activity have been observed in this species outside of Colombia [19–21]. The numbers of Micrurus obscurus encountered in various >1 month-long herpetological surveys indicate that this species can be found on average once every month to few months in appropriate habitat with sufficient survey effort [15,18,22]. 

In Colombia, M. obscurus has been documented to prey on the royal marsh snake (Erythrolamprus reginae), reticulate worm snake (Amerotyphlops reticulatus), speckled worm lizard (Amphisbaena bassleri), banded cat-eyed snake (Leptodeira ashmeadii), and Atractus sp. [23,24]. Outside of Colombia, M. obscurus has been reported to prey on various snakes, including the collared ground snake (Atractus collaris), golden-lipped marsh snake (Erythrolamprus chrisostomus), pygmy marsh snake (Erythrolamprus pygmaeus), banded cat-eyed snake (Leptodeira annulata), annellated coral snake (Micrurus annellatus), reticulate worm snake (Amerotyphlops reticulatus), common lancehead (Bothrops atrox), and unidentified Atractus and Dipsas species [10,11,16,25]. They have also been reported to prey on the reticulated creek lizard (Arthrosaura reticulata), forest whiptail (Kentropyx pelviceps), and caecilians [16,25,26]. 

An unidentified scolopendrid centipede preyed on a small M. obscurus specimen from Peru [27]. When threatened, this species typically flees, but it has also been documented to move erratically, hide the head beneath the body, dorso-ventrally flatten the body, and engage in a tail display [22,28,29]. The resemblance of M. obscurus to M. isozonus in the Colombian Orinoquia might represent a case of Müllerian mimicry; however, this requires confirmation [10,11]. In Brazil, the ectoparasite Amblyomma rotundatum has been documented on M. obscurus [30]. Micrurus obscurus is oviparous, but information on the reproduction of Colombian populations is lacking. In Ecuador, a clutch of 7 eggs was laid by one female [25].

The scientific name of this species is derived from the Greek roots Mikros (small) and oura (tail) referring to the short tails, which is a general trait of species from the Micrurus genus. The specific epithet (obscurus) means dark, dusky, or shady in Latin, which likely alludes to the melanic coloration of many specimens of this species [11]. In Colombia, this species is often referred to by locals as coral. 

Table 1. Summary of important biological, venomic, epidemiological and medical traits.

★ Poor confidence: Confidence for this species is poor due to the lack of data and information on Colombian populations. Therefore, most of our knowledge comes from a few studies and populations outside the national territory. LD50: median lethal dose, MCD: minimum coagulant dose, MDD: minimum defibrinating dose, DEM: minimum edema-forming dose, DHM: minimum hemolytic Dose, PLA2: phospholipases A2, SVSP: serine proteases, SVMP: metalloproteinases, NGF: nerve growth factor, CRISP: cysteine-rich secretory protein, CTL: C-type lectin/lectin-like, DIS: disintegrins, KUN: Kunitz peptides, BPPs: bradykinin-potentiating peptides, VEFG: VEFG: vascular endothelial growth factor, 3FTx: three-finger toxins, LAAO: L-amino acid oxidases.