Antlions: the truth behind Star Wars

Anyone who has ever seen The Return of the Jedi will be familiar with Luke Skywalker’s and Han Solo’s plight as Jabba the Hutt attempts to feed them to the sarlacc, which lurks in the bottom of the Great Pit of Carkoon. What might surprise you though is this isn’t far from the truth and many insects live in very real danger of coming face-to-face with such a creature, which is known as the antlion. 

As their comparison to the fictitious sarlacc suggests, antlions are ambush predators and are fairly common worldwide. In fact, they are found in almost every dry, arid environment and around 2, 000 species have been described so far that belong to the family Myrmeleontidae. Like many insects, antlions have a complex life cycle and pass through a larval form before they finally mature into adults. Due to this, the term ‘antlion’ is usually reserved to the larval form of the insect (which are sometimes called doodlebugs due to the spiralling trails they leave in sand while looking for a suitable place to build their trap), as an quick way to identify the form of the insect. 

Just like the sarlacc is, antlions are terrors and are capable of eating almost any arthropod that is unlucky enough to fall into one of their traps. Thus, their diet consists of a variety of insects that ranges from ants (obviously) and termites to small spiders! How their prey is caught however, depends on the exact species of antlion and their surrounding habitat, meaning that they could be lurking in foliage, hiding in the cracks in rocks and bark or be waiting in especially dug pits. 

Unusually among insects, antlions lack an anus and store all of their waste inside their bodies until they undergo metamorphosis (where it is discarded with the remnants of their cocoon).

It is the species that dig pitfall traps in sand that are particularly renowned however, and much research has been carried out into their trap-building behaviour. Typically, antlion pitfall traps are about 3 inches wide, 2 inches deep and are dug in finely grained, loosely packed sand. This criteria allows an antlion to create a steep, treacherous pitfall that their prey struggle to escape from once they've fallen into it as the walls crumble beneath their feet. To make their escape even harder, the antlion will then toss sand at the struggling insect to create a mini ‘landslide’ that helps to drag the struggling insect further into the hole. 

And once the insect has reached the bottom of the pit, it's all but game over and the antlion grabs it in its powerful mandibles, injecting deadly toxins and acids into its prey via several long spines that project from its hollow jaws. The antlion, which is firmly anchored in its trap by forward-facing bristles on its legs and body (that prevent it being dislodged and pulled from the pit), then holds its prey still until it has died and sucks the fluid ‘mush’ from the insect - feeding in same grotesque manner as spiders do. And, once the antlion is full, it throws the withered husk of its prey from its trap in the same way as it tosses sand and sets about repairing its walls. 

Antlions can remain in this larval form for up to 3 years, depending of course on the exact species and the amount of prey that is available, before they encase themselves in a cocoon of silk underground. Here, antlions undergo a remarkable process called metamorphosis where they change into their large, adult form over the period of about a month. Once their transformation has finished, the insects emerge from the ground, wait for their bodies to dry out and harden, and take to the air in search of mates.

Depending on the species, antlion damselflies can vary from being fairly small with 2cm wingspans to being much larger with wingspans of 15cm! Adults are much bigger than the larval form and show the greatest difference in size in any holometabolous insect (one that completely changes form via metamorphosis).

Adult antlions are sometimes are sometimes called antlion damselflies (despite having no relation to the damselfly family), and, depending on the species, vary between remaining as fierce predators or switch their diet to eat pollen and nectar. As their nickname suggests, the adult form look similar to damselflies although they can easily be identified by their extremely long, clubbed antennae and very narrow wings. 

Oddly, antlion damselflies are rarely seen in nature because they are usually active in the late evening and are poor flyers so (rather ironically), are very vulnerable to predators. They can be a real nuisance in desert areas however, where they are more abundant, as they tend to swarm and can deliver a mildly painful bite to any humans that they land on!

So, you might agree then that antlions are interesting insects in their own rights - being such fierce and efficient predators - but, considering they are the inspiration behind one of Star Wars' most famous aliens, they become even cooler and are definitely well worth knowing about!

Beneath the trapdoor danger lurks...

Wherever you go, you are bound to find spiders. They are an ancient class of predator and have learnt to use poisons, brute force and complex webs of silk to terrorise and instil fear into animals on every continent of the world except Antarctica. 

Typically, an easy way to tell the rough age of a species of spider is by looking at the complexity of the web it spins and the general rule is that the more elaborate the web, the younger the species of spider. This makes sense really as it would be expected for more complex structures, such as web scaffolding patterns, to take longer to evolve! Thus, the infamous tarantulas, which use silk only to line their burrows for warmth, are among of the oldest species of spider on the planet. 

Trapdoor spiders are another ancient lineage of arachnid, which is suggested by the simple manner in which they use silk. They use silk for the same purpose as many more ‘modern’ spiders since they rely on it to convey vibrations to them to show that prey is nearby, but do not spin it into complex webs. 

There are more than 500 different species of trapdoor spider that have been described so far, which can be found in tropical regions all across Earth. Despite being large and looking fairly intimidating, trapdoor spiders are rarely aggressive and are not dangerous to humans.

So instead of building silk nets like many newer species, trapdoor spiders dig a deep burrow in the soil (some species make a long tube of silk instead) and spin trip-lines that radiate out from the tunnel’s entrance. The spider then lurks near the mouth of its burrow, touching its trip-lines, and waits for an insect to knock one of the threads. When this happens, the spider feels the vibration and lunges out to grab, bite and poison its prey. 

Many species of trapdoor spider take this ambush tactic a step further and actually build a covering over the hole of their tunnel. This ‘trapdoor’ is what gives the family of spiders its name and is cleverly made from materials surrounding the burrow, such as soil, vegetation and silk, so it is camouflaged perfectly with the ground! 

Species that make a trapdoor always hinge their covering at one end with thick webbing and hold it down tightly using special claws on the ends of their feet. When its trip-lines are activated, the spider flips open its trapdoor, explodes out of its burrow and drags the hapless insect back inside for its dinner! And because trapdoors are typically very large spiders, almost all insects are on their menu – with meals commonly including cockroaches, crickets, grasshoppers, beetles, moths and other spiders. 

As would be expected, trapdoor spiders invest such a huge amount of time and energy in digging their burrows that they are a very shy and reclusive species. In fact, trapdoors rarely leave their burrows at all and female spiders typically spend their full 20 year lifespan in one burrow! It is usually only males that venture out from their burrows and even then, only once they have matured sexually and are seeking a mate. Like all spiders, male trapdoors mature near to the end of their lives (which are much shorter than those of females) so are inclined to take huge risks in finding a mate before they die. 

Once a male spider has mated with a viable female, the male dies (often to be eaten by the female) and the female remains in her burrow to feed her spiderlings when they hatch. Shortly after hatching, the spiderlings venture out of their mother’s burrow to dig their own home using their front legs and specialised barbs on their fangs called rastellum that help them to move soil.

Watching from the waters

The Nile crocodile, Crocodylus niloticus, is one of the most feared animals in the world and is undisputedly the most dangerous species of crocodilian to humans - being estimated to kill around 200 people each year. This is mainly due to its close proximity to our settlements and its indiscriminate diet - with it hunting anything that moves! Growing as long as 16 feet (5 metres) and weighing up to 225kg (500lb), the Nile crocodile can be found through central and south-east Africa and on the western shores of Madagascar. 

This is believed to be one of the largest specimens of Nile crocodile ever caught! Its huge size makes it no wonder why many Ancient Egyptians incorporated the beast into their belief system and worshipped Sobek, the crocodile god that lived in Crocodilopolis - a great city of crocodiles!

Probably one of the main reasons that the crocodile is such a proficient predator and is so lethal to humans is because it is a silent ambush predator - its flat body allows it to remain completely submerged, even in the shallow waters by river banks; and it has slightly raised nostrils and eyes that can be poked above the surface while keeping everything else hidden underwater, allowing it to see and breath virtually unnoticed. This allows the crocodile to get within yards of its prey (including humans), completely unnoticed and once it is ready, it lunges out of the water. Once the crocodile has lunged it is normally too late for its victim due to the speed of the attack and the animal is then crushed in the crocodile's vice-like bite and dragged into the water. After it has bitten an animal, Nile crocodiles (as with most crocodilians), have an overwhelming instinct to role - this is commonly known as 'death rolling' and, by spinning like a corkscrew, the crocodiles tear huge chunks of flesh out of their prey. This helps to compensate for their ineffective teeth, which are unusually blunt for a predator.

A Nile crocodile that has caught a gazelle. Nile crocodiles can eat up to half their body weight at a time and their bite force has been measured to be as high as 5, 000 lbf (22N), which is like being hit by a very fast-moving truck! Like most crocodiles, N. niloticus has a primary and secondary bite where an individual bites its prey once and then re-bites it without relaxing their first bite, helping to drive its blunt teeth even further into the flesh of the animal.

Ambushing their prey in this manner means that they can remain motionless in the water for very long periods of time and so, can conserve enormous amounts of energy. Crocodilians can also reduce their energy expenditure even further by slowing down their breathing and reducing their metabolism using a sophisticated cardiac shunting system that diverts blood away from their heart. Although cardiac shunting mechanisms are found in many species of reptile none have one as advanced as crocodiles. This, along with the fact that they have the most advance heart physiology in the world, has led many scientists to believe that crocodiles were once endothermic (warm blooded) like mammals and birds! Such scientists believe that their warm blooded ancestors slowly evolved back into being ectotherms (cold blooded) when they began to ambush their prey from water since a cold blooded body-plan would be much more beneficial for such a strategy; mainly because it wastes much less energy than trying to maintain a body temperature that is hotter than the surrounding water - just think about how cold you get if you spend too long in a cool bath or pool!

Thus, crocodiles can remain even in fairly cool water for long periods of time and wait for a potential meal to come to them! This is usually when an animal ventures too close to the waters edge for a drink... Nile crocodiles don't even have to use their muscles to hold their head up so can save even more energy while they wait! Their lungs act as ballast tanks and when they are inflated with air, actually push the crocodiles snout and eyes up above the water level! In fact, crocodiles can slow down their energy expenditure so much that they can hold their breath underwater for up to 2 hours when they inactive; often, lying in little 'dens' that they've dug out of the riverbed with their arms.

Certain species of bird, such as the spur-winged plover (Vanelus spinosus), have been seen picking scraps of meat from between crocodile teeth. It is not known for certain whether the birds are merely 'running the gauntlet' to obtain food at great personal risk or whether crocodiles are allowing them to this; forming a mutualistic relationship where the birds are fed while keeping the crocodile's mouth and teeth clean.

Although Nile crocodiles often hunt via ambushing their prey, they can also hunt with a much more proactive and energetic approach - chasing after fish and eating them underwater. It is believed that Nile crocodiles prefer to eat larger terrestrial game that they hunt with surprise attacks preferentially and switch to smaller fish when they aren't available or during then night when their mammalian prey is less active. Nile crocodiles are thought to prefer to ambush mammals for two main reasons: firstly, since it is less energetically expensive as mentioned above; and secondly, because crocodiles are far-sighted underwater due to the closure of their protective nictitating, or 'third', eyelids. Closing their third eyelid helps to protect their eye from underwater debris but also bends the light that passes through it so that the lenses in their eye can't refract the light enough to focus on close-up objects. Obviously, this will severely reduce their ability to hunt underwater and hunting in such a manner would probably be impossible if they didn't have many sensory papillae around edge of their lower jaw. These papillae act a bit like whiskers in dogs and cats and are able to detect even very minute vibrations in the water, allowing the crocs to sense fish that are close to their mouth! Crocodiles use much more energy when hunting fish in such a manner and as a result, can only hold their breath underwater for about 15 minutes since their muscles require more oxygen.

Their ruthless ability to surprise their prey and the fact that they eat humans has undoubtedly earned the Nile crocodile a fearsome reputation as a heartless monster. Oddly however, this isn't true and Nile crocodiles are one of the few crocodilians that care for their young - with mothers watching over their nests from when they lay their eggs to when they hatch! Most crocodilians abandon their nests as soon as they have lain their eggs and leave their offspring to fend for themselves. Furthermore, many crocodilians are cannibalistic and will eat juvenile crocodiles so that they may actually kill their own young unknowingly...

The gender of crocodiles is determined by the temperature that the eggs are at during their incubation, with temperatures of 32 - 33C producing males. Anything warmer or cooler than this narrow temperature range produces females, which is of great concern to conservationist biologists since global warming may result in more females being born and less males! The small size of the baby crocodiles makes them very vulnerable to predation early in life, but as they grow bigger and, if all goes well, the crocodiles can live for up to 100 years!

The Nile crocodile then, is a brutal and ruthless predator that preferentially hunts by ambushing unsuspecting animals from water. It accomplishes this using a range of physiological and behavioural adaptations and techniques which allow them to get within yards of their prey, gliding through the water causing barely a ripple... Despite their danger to man and the polluting effects that our lifestyle has on the waters of their habitats, the Nile crocodile is thriving and is classified as being of 'Least Concern' by the IUCN. This is not surprising really, since crocodilians are ancient animals that even trod the world with the dinosaurs! Their famed resilience allowed them to survive through the catastrophe that killed off the once mighty dinosaurs; and maybe, will even mean that they will survive for long after man has disappeared...