Jackie Billotte is a Ph.D. student at Colorado State University researching tarantulas and tarantula conservation, in partnership with the Butterfly Pavilion. Her advisors are Dr. Ruth Hufbauer and Dr. Richard Reading.
It’s tough being a male!
Male tarantulas have a much shorter lifespan than females. Once they reach sexual maturity, some males become so focused on mating that they stop eating. With the extra energy required to find mates and produce sperm packets, this can lead to starvation. Plus, they are at greater risk of predation while they are traveling the prairie looking for females. If a male does make it through mating season, it will be impossible to survive its next molt (the shedding of the exoskeleton). When males mature, their anatomy changes and they develop bulbs on their pedipalps (appendages used to transfer sperm to females). This change means certain death for male tarantulas after reaching sexual maturity.
Small, silk covered holes dot the ground of Heartland Ranch Nature Preserve, owned by the Southern Plains Land Trust (SPLT). During the day, you might not think much of these holes or even notice them. Once the sun sets, however, there is a good chance that the hairy, eight-legged residents will make themselves known. Numerous Aphonapelma hentzi tarantulas, commonly known as Oklahoma brown tarantulas, call Heartland Ranch and the surrounding area, their home. Being a 4”+ spider means first impressions are tough. There is, however, far more to love about tarantulas then there is to fear.
For as infamous as tarantulas are, surprisingly little is known about their private lives. In part, this is due to the reclusive nature of tarantulas, who would prefer to stay hidden in their burrows away from the prying eyes of curious humans. Learning about any species requires observation. That is no small feat when the animal you are trying to learn about is an expert at remaining incognito. Which leads us back to the small, silk covered burrows scattered around the prairie.
If you want to know more about an animal, look at where it makes its home. In the case of A. hentzi, that home is in a rough neighborhood. Life on the prairie can be tough. Temperatures can vary widely throughout the year and are often accompanied by intense winds that last for days. Water is scarce, and when it does rain it can easily flood. There are also the neighbors to worry about. Tarantulas, especially young tarantulas, are easy prey for the birds, lizards, and larger arthropods that live beside them.
It would seem with so many dangers, the cards are stacked against a tarantula. Yet they persist. The success of A. hentzi and tarantulas in general, is in part due to their ability to stay safely inside their burrows. Unassuming and well-fortified, tarantulas can live their entire lives in one burrow. For a female A. hentzi, this can mean living in one burrow for up to three decades. Tarantulas rarely venture far from their burrows, save only for mature males during breeding season. A tarantula’s burrow can literally be the only thing between survival and imminent death.
So, what makes a location good for a tarantula to build its burrow? I don’t know. In fact, no one does, but hopefully my dissertation research being conducting this summer at Heartland Ranch Nature Preserve and several surrounding properties, in partnership with Colorado State University and the Butterfly Pavilion, will help us begin to understand what conditions tarantulas prefer for their burrows. We will be looking at what types of vegetation and soil textures in which burrows are found and if those conditions vary in areas that are grazed or that have not been grazed by domestic cattle. We will also look at how close burrows are to one another. Along with my advisors, Dr. Richard Reading and Dr. Ruth Hufbauer, and a group of dedicated volunteers (you have to be very dedicated to agree to go spider hunting during the height of the summer), I have been slowly walking, eyes glued to the ground, in search of those small, silk covered burrows. Tarantula burrows are unique, most notably they are big. They are also very round and there is always the silk.
Studying the vegetation, soil, and density of A. hentzi burrows can help us to understand how A. hentzi interacts with its environment and with each other. You should know, tarantulas do not like roommates. Each burrow contains one spider. The only exception to this rule would be a mother with her offspring. Tarantulas are uncharacteristically good mothers, for a time at least. During the first weeks of a tarantula’s life, they live with their hundreds of siblings, guarded by their mother. Once they have shed their skin (known as molting) twice, their mother sends them out to into the world. Unlike true spiders (like black widows or the common cellar spider) tarantulas do not disperse through ballooning. Tarantulas must walk from their mothers burrows out into the wild, in search of a place of their own. Dispersing by walking means that tarantulas are not as subject to chance when establishing a home, it also means they are limited to the area they can walk.
You wouldn’t know it by looking at them, but tarantulas are excellent long-distance walkers. Previous research on another tarantula species found that baby tarantulas can walk as far as 9 meters (48 feet) when dispersing. As adults, male A. hentzi walk for miles in search of a mate. Distance alone does not determine where a tarantula ends up. Plus, being cannibalized by a sibling is a strong motivator to find a place of your own. Examining burrow density will help us understand the levels of tolerance A. hentzi have for living near one another, and how concerns about territory are weighed against other environmental conditions. It is possible that a favorable microhabitat could increase the tarantulas’ tolerance to one another, allowing them to live closer together. Much like an apartment in the city, if the location is good enough, you can overlook being surrounded by neighbors.
Understanding how tarantulas live, can help us to understand more about the prairie ecology and where tarantulas fit in that ecology. Tarantulas may not be welcome guests to most people, but they play important roles in their ecosystems. They aren’t too picky about what they eat and will happily feast on both invertebrates and vertebrates, thereby helping keep the populations of several animals in check. Tarantulas start out very small (around 1/8”), and for most of their lives, they serve as a vital food source for birds, reptiles, and even other spiders (again, they are not picky about their meal choice. Cannibalism is not out of the question).
Learning about how our activities may affect the tarantula’s habitat is also important. Tarantulas are icons of the American West. In recent years, the tarantulas of southeastern Colorado have gained a renewed notoriety in the form of the annual tarantula “migration.” From late July until mid-October, mature male A. hentzi will leave the safety of their burrow and walk for miles, night after night, in search of a mate, a journey they will not survive. When the ground comes alive with giant spiders, it does not go unnoticed. Every year, humans also head out at night to witness this spectacular event. Learning about where tarantulas choose to live and how we can mitigate our impact on them, will help to ensure future generations don’t miss this opportunity.