Tarantulas In Our Backyard — Part II, What’s Their Story?
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Yesterday, I spoke a bit about the five tarantulas (at least) that live in our backyard. Today, I’m going to post a few more images and tell these spiders’ story. I’m hoping that you’ll wind up being as intrigued about tarantulas as I am.
I’ve gleaned much of what I’m going to say from Jillian Cowles’ wonderful book, “Amazing Arachnids.” I commend this book to anyone who wants to learn more than I can provide in this short post.
Tarantulas are an ancient family of spiders with representatives living throughout the world’s warmer climates — in North and South America, Africa, Asia, and Australia. There are about 900 species of tarantula worldwide. They come in a wide variety of sizes and colors, and the various species have adopted a wide range of lifestyles. There are brilliantly colored tarantulas. There are tree-dwelling tarantulas and tarantulas that spend their lives in burrows. The different species have adapted to habitats as wide-ranging as deserts and tropical rain forests. Arizona’s tarantulas all belong to the genus Aphonopelma. Within that genus there are several species, including the big Desert Blonde tarantulas that inhabit our backyard, but also i several species that have adapted to the highlands of our local mountains.
Tarantulas all share common characteristics, many of which they share with other spiders. All spiders have bodies that are divided into two sections. The front section, the cephalothorax, houses the spider’s “head.” The cephalothorax includes the spider’s sensory organs, its mouth parts, its brain, and the attachments to its eight legs. The rear section, the abdomen, includes digestive organs, but also the spider’s breathing apparatus, reproductive organs, and silk-manufacturing glands. Look closely at the tarantula depicted above and you’ll see that the cephalothorax is the large, relatively hairless area at the front of the spider. The hair-covered abdomen sits behind it.
Tarantulas have eight eyes, but these are tiny and they probably do no more for the spider than distinguish light from dark. In the next image you’ll see a couple of those eyes as tiny white dots at the front of the spider’s cephalothorax. In this image those two minuscule eyes are visible because they’re reflecting the light from my camera’s flash (I made all of these images in total darkness).
Tarantulas probably rely on their eyes only to tell them that it’s dark out and time to become active — our desert species are completely nocturnal.
Much of the tarantula’s cephalothorax contains the spider’s brain. Spiders are surprisingly brainy, with brains that are huge in proportion to their bodies.
If you look at the front end of the tarantulas depicted in the second and third images you’ll see two short “legs” attached to the front of these spiders’ “faces.” Those are the spiders’ pedipalps. They are modified mouth parts, which tarantulas use to grab prey. Male tarantulas have specially modified pedipalps that play an important role in reproduction. During mating, the males transfer sperm from their bodies to the females’ genitals with their pedipalps.
Between the pedipalps and not really visible in these images are the tarantulas’ chelicerae. These organs house the tarantulas’ fangs, needle-like structures that the tarantulas use to inject venom into their prey. The venom works well to paralyze invertebrates and other prey. However, it isn’t particularly potent. I’ve been told that a tarantula’s bite is about as painful as a bee sting. As I explained yesterday, tarantulas almost never bite humans and do so only when severely molested. People keep these spiders as pets and many tarantula owners handle their pets without fear of being bitten.
I’ve mentioned that tarantulas have extremely poor vision. They also lack ears, so they cannot hear, at least not the way we do. So, how do they react to their environment? Take a close look at the tarantulas in these images. Those thousands of hairs on the spiders’ bodies function as sense organs. These organs transmit the slightest vibration. Through these hairs a tarantula can “hear” what is out there. It can judge size, distance, and direction of anyone creating vibrations, whether those vibrations are from footsteps or from the air disturbance caused by sound waves.
All spiders are predators. the Desert Blonde “hunts” by hanging out at the edge of its burrow, waiting for an unwary insect to come strolling by. When one comes within range, the tarantula moves with surprising speed to pounce on it, immobilize it with a bite, and then suck the fluids from the prey’s body. It doesn’t sound like a very efficient hunting style, but on the other hand, tarantulas don’t need to eat very often. They have an almost astoundingly slow metabolism that enables them to go weeks or months between meals. Tarantulas spend most of their lives just sitting still.
Images made with a Canon 5Div, 100-400mm f4.5-5.6 zoom L lens, M setting, illuminated by Canon 600EX-RT flash, M setting, ISO 320, 1/160, first image f13, second image f16, third image f18.