Tropidoclonion & the Scorpions

The dolomite glades of eastern Missouri host a variety of arachnid and reptile life beneath the slabs. I’m very familiar with scorpions of the genus Centruroides, but never have I experienced such a sheer abundance of them as in this glade. For any rock, there was probably around an 80% chance of a scorpion dwelling beneath, and at times there were even three or four scurrying around. In spite of their secretive habits, striped bark scorpions (C. vittatus) are excellent climbers and emerge during the night to forage on vegetation. During seasons of high caterpillar and grasshopper activity, they can more easily be found hunting above the ground, though in glades this behavior leaves them especially vulnerable to predation under moonlight.

Striped bark scorpion (Centruroides vittatus) [3]
Brown tarantula (Aphonopelma hentzi) ♀ [3]

Scorpions are certainly formidable predators, but they are not the most fearsome in this landscape. The most powerful due to sheer size are the brown tarantulas (Aphonopelma hentzi), of which we found five— three females, a thinner darker male, and a light-colored juvenile only a few centimeters in length. Except for the female pictured above, all other adults were positioned at the entrance to their webbed funnel entrances. In response to disturbance, they shuttled down to safety but could be lured out by stroking a blade of grass lightly against the sides of the tunnel to resemble prey. Brown tarantulas spend the majority of their lives as sedentary sit-and-wait predators. However, they are also quite capable of traveling great distances. During early summer to the beginning of winter, males wander upwards of a kilometer from their homes to locate a potential mate. These ‘migrations‘ are crucial for reproductive success but inevitably have a high mortality risk for these long-lived arachnids. It isn’t uncommon to find males that are emaciated from their journeys, which can last a few weeks before they establish themselves in a new refuge.

Juvenile brown tarantula (Aphonopelma hentzi) [3]
Northern black widow (Latrodectus variolus) ♀ [4]; when touched, it spun silk while exuding fluids
Striped bark scorpion (Centruroides vittatus) [3]
Weak-leaf yucca (Yucca cf. flaccida)
Bigfruit evening primrose (Oenothera macrocarpa)
Little brown skink (Scincella lateralis) [4]

Arthropods are not the only prey of tarantulas. Small lizards and snakes must also carefully navigate the moist soils to tuck themselves away but avoid cavities that are deceptively dark and quiet. This is exactly the case for snakes like centipede eaters and below, the lined snake (Tropidoclonion lineatum). I’ve always been captivated by miniaturized reptiles, whose diversity is often overlooked in comparison to larger and more flamboyant species. Small size brings quirky adaptations to highly specialized ecological habits. In the case of lined snakes, they feed almost exclusively on earthworms. Limited in gape, they must be purposeful when hunting worms. After following a worm’s scent, lined snakes will move their heads forward slowly until they practically touch the worm’s body. Then in a jolt, they will bite a midsection of the body and retract their heads, turning side to side to resist the worm’s muscular contractions. The snakes also tend to make reaching movements with their tails at the same time, and if a rigid object is found, they will grasp it for use as an anchor. Being so small, lined snakes may otherwise get overpowered and dragged by an earthworm!

In contrast to how consuming long prey items linearly like most snakes, Tropidoclonion folds the worms in two as they work their jaws around them. This method makes it difficult for the worm to squirm out of the snake’s mouth in any particular direction. If escape is imminent, lined snakes can sever the worm in place, ingesting whatever portion of the worm’s body they can get. Almost nothing about the ecology of lined snakes has been documented, but here I’ve summarized some fascinating aspects of their feeding behavior from a natural history paper from 1947. Only a few other papers that concern reproductive biology have since been published, despite 74 years having passed…

Lined snake (Tropidoclonion lineatum)
Purple coneflowers (Echinacea simulata or E. pallida)
Six-lined racerunner (Aspidoscelis sexlineatus) [4]
Sweet pea (Lathyrus latifolius or L. sylvestris)
Butterfly milkweed (Asclepias tuberosa)

Leave a Reply

%d bloggers like this:
close-alt close collapse comment ellipsis expand gallery heart lock menu next pinned previous reply search share star