Little Killers: The Ferocious Lives of Puny Predators
CHAPTER 1 KILLERS AROUND US A group of microscopic copepods Far from land hundreds of feet below the ocean surface a copepod KOH-peh-pod swims through dim twilight waters The copepod measures only a tenth of an inch 2 5 mm but has two ridiculously long antennae sweeping out from its head The animal uses its antennae to locate microscopic plants called phytoplankton Like a contented cow the copepod grazes on one tiny plant after another All seems peaceful until 4
in darts a nightmare out of a science fiction movie The sudden arrival looks like a slim transparent torpedo Instead of a face it has a menacing mouth surrounded by a nest of grasping hooks or spines It has stubby horizontal fins and a fanlike tail and by wriggling up and down it can accelerate to terrifying speeds Faster than you can shout free food the tiny torpedo seizes the copepod with its hooks and opens its mouth wide The copepod struggles to get away but it is no use In an instant the predator swallows the copepod whole ALARMING ARROWS The torpedo shaped animal is a chaetognath KEE-tug-nath or arrow worm Most people have never heard of chaetognaths but they are among Earth’s most ferocious predators Most chaetognaths live in the upper layers of the world’s oceans and most are planktonic they are carried from place to place by ocean currents Chaetognaths though can also live in tide pools on the seafloor and in the very deep sea The word chaetognath is Latin for bristle jawed An arrow worm right uses darting speed and grasping hooks to seize tiny fish and other prey 5
Hangin Out Chaetognaths spend a lot of time hanging suspended in the water Their horizontal fins help keep them from sinking very rapidly When they do sink or detect prey they dart forward using rapid muscle contractions in their bodies Chaetognaths have superb tools to help them ambush and seize their prey Their bodies are see through making them almost impossible to spot especially in the dim regions where they prefer to hunt Tiny hairs on their skin help them detect the smallest water movements allowing them to target their prey Perhaps most impressive are the chaetognath’s mouthparts Hooks or spines surround the mouth and are used for grasping prey while needle-sharp teeth inside its mouth help the animal pierce and swallow prey Many chaetognaths can even inject poison into their victims An arrow worm’s see through body and slim profile help it sneak up on prey and escape the notice of other predators 6
Chaetognaths first appeared on Earth at least five hundred million years ago Since then their bodies have changed very little a sign that they are very well adapted to living where and how they do Because of this scientists consider them one of Earth’s most successful predators But chaetognaths also are some of Earth’s smallest predators While a few deep water species can grow to 4 or 5 inches 10 to 12 cm long most are shorter than a pencil eraser Chaetognaths however are far from Earth’s only puny-sized predators Fisherman’s Foe Besides eating copepods chaetognaths are major predators of small fish and fish larvae They may even control or limit some fish populations around the world TINY KILLERS When most of us hear the word predator we imagine lions sneaking through tall grass after zebras or great white sharks tearing seals to shreds That’s no surprise Large predators from wolves to polar bears to orcas are some of Earth’s most impressive animals But the vast majority of Earth’s predators aren’t humongous lion or whale sized creatures Many such as spiders and ladybird beetles are so small that you can easily overlook them while taking your dog for a walk Others such as chaetognaths are so little you often need a microscope to see them Some chaetognaths can eat up to a third of their weight each day What makes these little killers so successful MICRO ADVANTAGES Like larger predators small predators come equipped with an arsenal of weapons to help them catch and subdue their prey These weapons such as the teeth hooks and transparent body of a chaetognath are perfectly adapted to each predator’s size habitat and way of life Little killers also have a couple of advantages over other predators 7
