Venom Metering for Prey

For snakes it was found that venom was expended by coordination between various muscles controlling the jaw, fang, and venom gland (Harrison et al. 2008 ). These muscles that control the amount of venom expended are believed to be controlled by the central nervous system allowing for the snake to meter the amount of venom given (Gennaro et al. 2001). This could also be how many other species are able to meter venom for predatory use but has not been fully studied. Venom metering for predatory strikes has been linked to the size of the prey, the amount of struggle, and the type of the prey species.

Prairie Rattlesnakes (Crotalus viridis) were found to control the amount of venom given for different species. For mice it would bite and release to envonmate it, but for songbirds it was found to hold the prey. This is believed to reduce the risk of the songbird flying away and the rattlesnake losing its meal, but it also increases the prairie rattlesnakes risk for injury. To reduce this risk, the rattlesnake will increase the amount of venom given to immobilize the songbird before it can hurt it (Gennaro et al. 2001).

The wandering spider (Cupiennius salei) was found to be capable of injecting precise venom quantities in order to immobilize its meal. The wandering spider will inject less venom in insect species that are un-problematic and have less of a chance of escape. Stick insects and crickets are easily overcome, but beetles and blowflies have higher risks and are found to receive more venom because of it. In the case of blowflies it was found that they produce high frequent vibrations with their wings when trying to fly away, which cause the spider to give more venom so as not to lose its prey. Beetles were found to receive the highest amount of venom most likely due to their hard sclerotisation and chance of hurting the spider (Kuhn-Nentwig et al. 2002).

The Cottonmouth (Agkistrodon piscivorous) was found to regulate the amount of venom given due to the size of its prey. A study found that the cottonmouth would inject similar venom into mice and rats, but higher quantities into guinea pigs. This was also found in the Northern Pacific rattlesnake (Crotalus oreganus) between large and small mice. This show us that there is an intrinsic ability for the snake to control the amount of venom given (Gennaro et al. 2001).

Gennaro, J. Hayes, W. Herbert, S. Rehling, G. (2001) 'Factors that influence venom expenditure by viperid and other snakes during predatory and defensive contexts'. In Biology of the Vipers (ed. Schuett, G. Hoggren, M. Greene, H). Traverse City: Biological Sciences Press

Harrison, J. Hayes, W. Herbert, S. Wiley, H. (2008) 'Spitting versus biting: Differential Venom Gland Contraction Regulates Venom Expenditure in the Black-Necked Spitting Cobra: Naja nigricollis nigricollis'. Journal of Herpetology, Vol. 42, Iss. 3, Pgs. 453-460.

Kuhn-Nentwig, L. Nentwig, W. Wigger, E. (2002) 'The venom optimisation hypothesis: a spider injects large venom quantities only into difficult prey types'. Toxicon, Vol. 40, Iss. 6, Pgs. 749-752.