American "superbat" (Antrozous pallidus) is immune against scorpion venom

The Pallid Bat (Antrozous pallidus). Photo: Courtesy by Connor Long (C)

A few weeks ago an article by  Bradley Hopp and co-workers presented a study of the Pallid Bat (Antrozous pallidus) using the Arizona Bark Scorpion (Centruroides sculpturatus Ewing, 1928) as prey. The Arizona Bark Scorpion is the most venomous scorpion in the US, and the researchers observed that the hunting bats were stung by their prey without any serious symptoms.

Systematic observations and experiments with injections of scorpion venom in the bats confirmed that The Pallid Bat is probably resistant to the venom of the bark scorpion. An altered sodium ion channel function may partly be the mechanism for this resistance.

Abstract:
The pallid bat (Antrozous pallidus), a gleaning bat found in the western United States and Mexico, hunts a wide variety of ground-dwelling prey, including scorpions. Anecdotal evidence suggests that the pallid bat is resistant to scorpion venom, but no systematic study has been performed. Here we show with behavioral measures and direct injection of venom that the pallid bat is resistant to venom of the Arizona bark scorpion, Centruroides sculpturatus. Our results show that the pallid bat is stung multiple times during a hunt without any noticeable effect on behavior. In addition, direct injection of venom at mouse LD50 concentrations (1.5 mg/kg) has no effect on bat behavior. At the highest concentration tested (10 mg/kg), three out of four bats showed no effects. One of the four bats showed a transient effect suggesting that additional studies are required to identify potential regional variation in venom tolerance. Scorpion venom is a cocktail of toxins, some of which activate voltagegated sodium ion channels, causing intense pain. Dorsal root ganglia (DRG) contain nociceptive neurons and are principal targets of scorpion venom toxins. To understand if mutations in specific ion channels contribute to venom resistance, a pallid bat DRG transcriptome was generated. As sodium channels are a major target of scorpion venom, we identified amino acid substitutions present in the pallid bat that may lead to venom resistance. Some of these substitutions are similar to corresponding amino acids in sodium channel isoforms responsible for reduced venom binding activity. The substitution found previously in the grasshopper mouse providing venom resistance to the bark scorpion is not present in the pallid bat, indicating a potentially novel mechanism for venom resistance in the bat that remains to be identified. Taken together, these results indicate that the pallid bat is resistant to venom of the bark scorpion and altered sodium ion channel function may partly underlie such resistance.

Reference:
Hopp BH, Arvidson RS, Adams ME, Razak KA. Arizona bark scorpion venom resistance in the pallid bat, Antrozous pallidus. PLoS One. 2017;12(8):e0183215. [Open Access]

Thanks to Matt Simon for informing me about this article.

Scorpion eating bats

Even though scorpions are notorious predators with a venomous sting, they also are prey for other predators including several vertebrate predators like reptiles, birds and mammals. Marc Holderied and co-workers have published an interesting study showing how the Hemprich's long-eared bat (Otonycteris hemprichii) prey on scorpions in Israel.

Interestingly, the bats didn't differ between potent species like Leiurus quinquestriatus and more harmless species like Scorpio maurus, and stings didn't change the bat's behavior and caused no sign of poisoning.

Abstract:
Over 70% of the droppings of the gleaning bat Otonycteris hemprichii can contain scorpion fragments. Yet, some scorpions found in its desert habitat possess venom of the highest known toxicity, rendering them a very dangerous prey. In this study, we describe how O. hemprichii catches and handles scorpions, quantify its flight and echolocation behaviour in the field, investigate what sensory modality it uses to detect scorpions, and test whether it selects scorpions according to their size or toxicity. We confirmed that O. hemprichi is a whispering bat (approx. 80 dB peSPL) with short, multi-harmonic calls. In a flight room we also confirmed that O. hemprichii detects scorpions by their walking noises. Amplitudes of such noises were measured and they reach the flying bat at or below the level of echoes of the loess substrate. Bats dropped straight onto moving scorpions and were stung frequently even straight in their face. Stings did not change the bats’ behaviour and caused no signs of poisoning. Scorpions were eaten including poison gland and stinger. Bats showed no preference neither for any of the scorpion species nor their size suggesting they are generalist predators with regard to scorpions.

Reference:
Holderied M, Korine C, Moritz T. Hemprich's long-eared bat (Otonycteris hemprichii) as a predator of scorpions: whispering echolocation, passive gleaning and prey selection. J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2010. Ahead of Print Nov 18. DOI: 10.1007/s00359-010-0608-3. [Subscription required for fulltext]