II. SAND-DWELLING ANIMALS

The Florida mouse escapes its predators and the hot, dry conditions by being nocturnal and by burrowing. It frequently uses gopher tortoise burrows and will construct its own burrows and nest chambers off the main gopher tortoise burrow. While feeding, the ¼-inch long, flightless scrub pygmy mole cricket excavates extensive burrows that branch and curve about 3mm under the sand's surface. It eats microscopic algae, which grow in a layer underneath the translucent grains of sand in open, sunny locations of scrub. Burrows are best seen a couple of hours after a rain because the sand over the burrow dries quickly and appears white while the surrounding sand is still damp and gray. The blue-tailed mole skink, occurs only on the Lake Wales Ridge, and is most frequently found at a depth of 1-2 inches under the sand's surface. The young of the southeastern skink also have a blue tail, but these lizards spend their time above ground and do not burrow in the sand. When threatened, the blue-tailed mole skink wriggles and burrows, while the southeastern skink scurries away rapidly. Like the sand skink, blue-tailed mole skinks lay relatively few eggs-which makes it more difficult for populations to recover from disasters. The small, blind, and flightless scrub scarab beetle spends its entire life in sand located in sunny, open areas of scrub. This beetle is commonly found in sand around harvester ant hills and clumps of grass where it can find small bits of dead plant material to eat.

Introduction

For sand-dwelling organisms, the Florida scrub is a vast sea of sand with very different rules for living. These rules are not so obvious to humans. Our experience with sand is limited. We may notice that sand is more difficult to walk on than dry clay soil, but a bit easier than walking in mud. We dig easily in sand-except when we encounter tree roots-and watch how the sides of a hole tend to collapse. We don't need special sand shoes. We don't need special sand shovels. Most scrub animals, however, live immersed in sand. For them, sand is a whole environment. For them, sand offers special opportunities and challenges. This means that animals that live in sand often need different adaptations from animals that live in other kinds of soil. Therefore, the animals found in sand are often different species from animals that live in other places. Some of the animals that live in the sand of Florida scrub live nowhere else on Earth.

The activities in this chapter focus on the remarkable adaptations of animals that live in sand. In a larger sense, these activities are designed to help students understand that while the features of these animals may seem like bizarre and meaningless distortions, there are actually important adaptations to sandy conditions. This is a challenge! An ant lion larva really does look strange! And students see weird things in our culture that do not have functional meaning or purpose---like ties worn by businessmen and very baggy pants worn by students.

To help students understand adaptations, you can present them as tools and skills. (This approach is a little flawed because adaptation actually implies a long, slow process of change without any preset goal. This means that animal adaptations are often less perfect than you'd expect if these skills and tools had been designed by an engineer.) Students need to understand that an animal's structure (tools) and behavior (skills) have functional meaning. For example, the teeth on the inner side of the ant lion's jaw have a function: they hold the prey in place while the hollow tips of the mandibles inject digestive fluid. They are the tools of the ambushing predator. The burrows that a pygmy mole cricket makes on the surface of the sand after a rain demonstrate how the cricket is looking for and eating algae that live under the surface. Making these burrows is an instinctive skill of the pygmy mole cricket.

The activities in this chapter focus on insects and spiders because their tools and skills are easy to see. Their tools are built into their exoskeletons. Their skills are mostly instinctive. Both the ant lion and the scrub burrowing wolf spider exhibit one of the most interesting features of animal adaptations---they are both ambushing predators that eat small scrub insects. The tools and skills of these two animals, however, are completely different.

Background Information

Because the Florida scrub is a very old type of sandy habitat, it has many of its own animals with their special adaptations. Two particular characteristics of sand have shaped the adaptations of these sand-dwelling animals.

One characteristic of the scrub environment that is very important to small scrub animals is sand's permeability, its "digability," its "burrowaceousness." (The right word for this doesn't exist!) Permeability means that animals can swim and burrow through the sand with remarkable ease. They can excavate tunnels and underground chambers. Larvae of root-eating beetles can move around a plant, grazing on its rootlets. Larvae of predatory beetles and flies can hunt for the beetle larvae or for underground caterpillars. Snakes can move along the subways left by fast-moving moles. Ants and termites build subterranean corridors and chambers throughout. Some species such as the sand skink, the blue-tailed mole skink, and the short-tailed snake spend almost their entire lives underground. A wingless, blind scarab beetle species probably never emerges from the sand. Several species of tiny yellow ants never appear on the surface, only the males and queens emerge for their mating flight. Several species of beetles have males that emerge from the sand and fly to disperse. However, the females are flightless and remain buried just under the surface of the sand. Since the sand is so permeable, animals can easily move up or down to find warmer or cooler, damper or drier regions.

A second major feature of sand, though less important than its permeability, is its abrasiveness. This is particularly significant to insects. Many sand-dwelling insects, especially those that swim through the sand, are heavily armored. They may also be covered with backward-pointing hairs that hold sand away from the body, and keep the insect from slipping backward as it moves through the sand
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Revised 24 April 2000 by Fred Lohrer.