Snakes vs crayfish: How snakes snack on crunchy crustaceans

When imagining the tasty treats a snake might seek, we typically might think of mammals, amphibians, or fish. While these soft-bodied animals may be popular prey choices amongst snakes, a few special groups prey upon crunchier animals, such as crayfish. The shell on a crayfish provides some unique challenges for a hungry snake- shells cannot be easily manipulated to fit in tight spaces, and the hardness of some shells may make it difficult to break larger shells. The unique body plan and behavior of snakes can restrict the prey that are available to them- without limbs, it is difficult to manipulate prey items and prey capture is often limited by the gape size of a snake’s mouth.

To better understand how feeding performance may be affected by anatomical form and prey type, Gripshover & Jayne (2021) compared the maximal mouth gape, size of captured prey, and how prey affected snake behavior in two species known to eat crustaceans. The first species, Regina septemvittata, primarily feeds on soft-shelled crayfish, whereas the second species, Liodytes alleni, can eat hard-shelled crayfish. These species each evolved this dietary specialization for crustaceans independently.

Figure 1. (From Gripshover & Jayne, 2021). Computed tomography scans of R. septemvittata (A) and L. alleni (B) along with the relative contributions of maximal gape area by various parts of the skull. SW: skull width, QD: quadrate, LJ: lower jaw, and SI: skin and lower jaw intermandibular ligament.

The authors measured the maximal mouth gape area in each of the species to compare to the relative area of the prey items as well as the mass of the prey items (see Figure 1). They collected the stomach contents to record prey characteristics, and they measured the time it took snakes to successfully capture, handle, and swallow prey.

While L. alleni had a larger maximal mouth gape, R. septemvittata consumed larger relative prey, using a higher fraction of their maximal mouth gape capacity. Prey handling differed between the types of prey and between the two snake species (see Figure 2). In L. alleni, which uses the body to restrain prey, as the relative area of the prey increased, restraint behaviors increased. This led to faster and more successful prey capture events compared to R. septemvittata. L. alleni handled the soft-shelled crayfish faster than hard-shelled crayfish, suggesting that the type of prey affects the handling time. While R. septemvittata did not restrain prey, they used a rare behavior in breaking a prey item into smaller pieces to consume. This behavior allows for predation on prey items that are too large to fit the maximal mouth gape area and may be especially beneficial in certain life stages. For example, there are very few small crayfish around the time of year that juvenile snakes hatch. But the ability to bite off just the limbs of a large crayfish allows juvenile snakes to get the food that they need before they reach the size needed to consume whole prey.   

Figure 2. (from Gripshover & Jayne, 2021). Lack of limbs does not prevent some snakes from restraining prey. L. alleni can restrain prey by manipulating the body into a series of shapes. A. U- loop shape with a soft-shelled crayfish. B. Pinning a hard-shelled crayfish. C. Coiling a soft-shelled crayfish.

The authors comparisons of predation in these two snake species uncover interesting relationships between anatomy, behaviors, and ecology. There are so many factors that go into the predator-prey relationship, including the anatomical forms of both predator and prey, escape and defense behaviors of the prey, attack and restraint behaviors of the predator, the availability of prey, and the environment in which these interactions take place. We see very different approaches in how each of the species successfully captures a challenging prey item. Going forward, we will continue to learn more about how different species accomplish challenging feats and through this, we will better understand the larger patterns of variation in a phylogeny!

Amanda M. Palecek-McClung is a PhD student at Clemson University. She studies functional morphology, biomechanics, and adhesion mechanisms in fish and other vertebrates. You can find more about her at ampalecek.weebly.com or contact her at apalece@g.clemson.edu.

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