Llaneran Coral snake
Micrurus isozonus

There are no published cases of envenomation by Micrurus isozonus, and no records of snakebite accidents caused by this species have been recorded in Colombia’s National Public Health Surveillance System (SIVIGILA, Spanish acronym). Information on the composition of its venom is also lacking. The symptoms of envenomation by M. isozonus are likely similar to those observed in cases of envenomation by other Micrurus species. 

The symptoms of bites by Micrurus include various local and systemic symptoms depending on the grade of envenomation. Mild envenomation results in exclusively local symptoms, including redness of the skin (erythema), mild local pain that may radiate to the entire limb, and swelling (edema). Muscle pain (myalgia) and muscle twitching (i.e., fasciculation) are also possible [1,2]. Moderate envenomation results in more severe redness of the skin, and pain, as well as burning, stabbing, or stinging sensation (dysesthesia), prickling sensations (paresthesia), drooping of the upper eyelid (palpebral ptosis), weakening of the muscles used to produce speech (dysarthria), and altered taste (dysgeusia) [1,2]. Severe envenomation can cause flaccid paralysis within the first 30 minutes of the bite, excessive salivation (sialorrhea), severe dysarthria, paralysis of the flexor muscles of the neck (“broken neck sign”), and shortness of breath (dypsnea) [1–3].

Life-threatening symptoms can appear rapidly after envenomation by M. isozonus. Rapid medical attention, especially antivenom therapy, is thus essential for ensuring the safety of patients bit by this snake [4]. The first action that should be taken after a bite by M. isozonus is to immobilize the bitten limb [5]. Any local treatments that delay arrival to a medical facility, including those lacking any clinically demonstrated efficacy (e.g., the use of ice, medicinal plants, or oils on the site of the bite) should be avoided. 

Upon arrival at a medical facility, the antivenom treatment regimen should be administered once envenomation is confirmed (mild, moderate, or severe), and the geographical origin of the accident should be considered [2]. In cases occurring in the Andean, Caribbean, and Pacific regions, five vials of INS antivenom may be required, while for cases in the Amazon or Orinoquía regions, 10 vials are needed [2,3]. These antivenom dosages are the same for both children and adults [7], and the application of antivenom should only be performed by qualified medical personnel [1,6]. 

In Colombia, M. isozonus occurs in the Trans-Andean region, throughout the Orinoquia, and in the foothills of the Andes up to 500 m [11]. It has been documented in the following departments: Arauca, Bolívar, Casanare, Meta, and Vichada [11–14] (Figure 1).

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Figure 1. Geographic distribution of Micrurus ancoralis 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 fossorial snake can be found in diverse habitats, including tropical deciduous forest, tropical thorn woodland, savanna, and gallery forest, but appears to be most common in semi-arid and seasonally dry regions [11,12,15,16]. It can also be found in disturbed habitats, such as pasture, secondary growth, and suburban areas [11,13]. Micrurus isozonus is surface-active in the morning, evening, or at night, but some populations in Venezuela appear to be chiefly nocturnal in their movements [17–20]. Although it is considered common throughout its range in Venezuela, it might be less common and widespread in Colombia based on the few numbers of localities from which it has been collected [8,12]. Given its apparent preference for semiarid habitats, M. isozonus could potentially colonize more humid areas at higher altitudes that have been aridified by human activities. 

In Colombia, M. isozonus has been documented to prey on Erythrolamprus bizona [13]. Outside of Colombia, M. isozonus has been reported to prey on lizards and snakes, including microteiids (Bachia spp.), watersnakes (Helicops sp.), blindsnakes (Leptotyphlops sp.), and Boddaert’s tropical racer (Mastigodryas boddaerti) [11,13,18]. No records of predation on M. isozonus have yet been reported. When threatened and unable to flee, M. isozonus often raises and curls its tail; it is also capable of vigorously defending itself [11,21,22]. Micrurus isozonus resembles M. obscurus in the Colombian Orinoquia, and whether this represents a case of Müllerian mimicry requires confirmation [11,13]. 

Unidentified nematodes have been reported in the intestines of this snake, and unidentified ticks have been observed on the infracephalic scales [13]. M. isozonus is oviparous, and no information on its reproduction is available for Colombian populations. In Venezuela, a 68-cm long female laid a clutch of 6 eggs, averaging 26.1 × 10.7 mm in size, on April 27 shortly before the start of the wet season [13,23]. Reproductive activity in M. isozonus is likely tied to the distribution of moisture throughout the year, with mating occurring in the dry season and oviposition before the beginning of the wet season [13,18]. More work is needed to clarify many aspects of the natural history of this poorly known snake in Colombia.

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 is derived from two Greek roots: isos (equal) and zone (belt), which allude to the approximately equal length of the black and white rings [11,13]. In Colombia, this species is often referred to as coral or coral llanera [15].

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

★ Poorly Reliable: 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: vascular endothelial growth factor; 3FTx: three-finger toxins; LAAO: L-amino acid oxidases.​