Face off: the great white shark vs the killer whale

Our oceans are full of predators, ranging from tiny carnivorous fish to poisonous snakes; from poisonous snakes to electrocuting eels; from electrocuting eels to murderous dolphins. In short, predators are everywhere and none are more feared than the great white shark and the killer whale. Both of these animals are titans – huge animals that can hunt and kill almost anything they want to (and yes, humans are included). But which of these is the top predator? Which of them would best the other in a fight?

The great white shark, Carcharodon carcharias, is one of the most feared animals in the oceans. The sharks often hunt by taking advantage of their huge strength, ambushing the seals they hunt from underneath while they rest on the surface. Unfortunately, surfers resting on their boards can look very similar to seals from underwater, which is believed to be the main cause of great white shark attacks on humans.

I’m sure many of you are thinking that this would be the great white. And why not? Great whites have been known to kill humans and there is a huge ‘fear culture’ around sharks after Peter Benchley’s Jaws was televised in a film. You would be wrong, however, and there is a case that to show that it is in fact orcas that rule the oceans.

In the first instance, you have to remember that orcas are social and hunt in packs (which has actually earned them the nickname of ‘the wolves of the sea’). Obviously, this provides killer whales with a huge advantage over the solitary great white and orcas can bring down prey much larger than themselves. In fact, orcas have even been known to go after small female sperm whales (which are actually the largest predator alive), so picking off a lone great white shouldn't be too much of a problem for them!

Like humans and other primates, killer whales are extremely social and live most of their lives in tight-knit social groups of close family members. To prevent the inbreeding that this would inevitably lead to, male orcas usually leave their maternal pod once they sexually mature and actively seek another pod to live with for the rest of their adult lives.

Secondly, you have to consider the intelligence of killer whales, which are part of the same family of oceanic dolphins (Delphinidae). All of the members in this family are extremely resourceful and have been seen to use complex, highly sophisticated tactics while hunting their prey. In fact, killer whales have actually been observed practicing to hunt (click here for more information) and it is one such tactic that leaves little doubt that orcas are hierarchically above great whites.

As you may or may not already be aware, orcas have different cultures (in much the same way as humans do) and different pods in various locations around the world specialise in hunting certain animals. Common examples of their sources of prey include fish and water mammals, such as seals. But it is the pods that specialise in hunting sharks that are really relevant for this post. Such orcas have realised and taken advantage of two very simple aspects of shark anatomy:

• Firstly, most species of shark go into a hypnotic state of sleep called tonic immobility when they are turned upside down
• Secondly, sharks have to keep swimming in order to breathe and, as soon as they stop moving, water ceases flowing through their gills and they begin to suffocate

Since great white sharks have to keep swimming in order to breathe, they have developed a remarkable method of sleep where they rest each half of their brain separately. This allows the neurotransmitters in their brain to recover to normal levels after waking activity, while simultaneously allowing the shark to keep moving and remain alert for prey and danger.

By taking advantage of these two simple facts, orcas can kill sharks extremely easily and with very little risk of injury to themselves (i.e. the sharks can’t fight back). To do this, orcas take advantage of their extreme agility and ambush sharks from above. As they near the unassuming shark, they bite it just above their dorsal fin and use their strength and body weight to roll the shark upside down, meaning that it falls asleep and stops struggling. Then, it’s just a simple case of the killer whale holding its breath while it waits for the shark to suffocate and die!

This tactic is merciless and brutal, but it is extremely effective and scientists have actually seen killer whales using it on great whites off the coast of California! What is also interesting, other than orcas being able to kill great whites so easily that is, is that great whites (like many species of shark) release chemicals called ‘death signals’ into the water when they are killed. These signals drive off all other great whites for miles and, for many years, scientists were baffled by why the massive predator suddenly vanished from Californian waters. It was only when they realised that the exodus of great whites coincided with the seasonal arrival of a certain pod of orcas from Antarctica that they put two and two together and began to observe how the two predators interacted. Just imagine their surprise!

Brief hiatus

Hi!

As I'm sure you've undoubtedly noticed, there's been a a significant lack of new posts on here lately. This is mainly because things have been pretty hectic recently and, for the time being, it's looking like my free time is going to reduce even further! Due to this, I'm announcing (rather regretfully) that I'll be taking a short break from writing on this blog.

I plan for this break to continue until things have settled down a bit, which (for the moment) I'm hopeful will happen fairly quickly. Thus, I'm expecting to resume posting on here within the next few months and already have loads of great posts planned out for you so be sure to check back soon!

All the best,

David

Short Alzheimer's disease survey

Hi all!

I have a friend at university who's conducting a research project into various diagnostic methods for Alzheimer's disease. As part of her project, she has to gather peoples feedback on such testing methods and has created a questionnaire in order to do this.

The questionnaire (which is anonymous) is very short, being formed of 9 multiple-choice questions, and will take no more than a few minutes of you time. Please help her out by taking the survey and I'm sure she would be grateful for your help!

Thanks,

David

THIS PROJECT HAS NOW BEEN COMPLETED. THANK YOU TO EVERYONE WHO TOOK THE TIME TO COMPLETE THE QUESTIONNAIRE.

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!

Round & round the straight line

If you’ve ever switched a light on in the dark you’ll have no doubt noticed the rather strange effect it has on moths, which are soon attracted to the light and begin to spiral round it for hours. Many people wonder what causes this bizarre behaviour and, at the moment, there is no definitive answer as even entomologists (the scientists who study insects) find it confusing. 

This isn’t to say that they don’t have theories regarding this behaviour however, and there is one main explanation that is generally accepted among the entomological community that seems to have some scientific evidence. This theory is surprisingly simple and basically works off the principle that lepidopterists (the family of butterflies and moths) use light to navigate when they are flying. 

Like many insects, moths have very poor vision that is mainly used just to detect light and movement.  Most of the information about their surroundings actually comes from their highly developed antennae, which provide them with an incredibly sensitive sense of smell. In fact, the antenna of male moths (pictured above) are so sensitive in some species that they can detect a single molecule of a female moth's sex pheromone in 1 cubic yard of air - allowing them to smell the moth from 11 kilometres away!

So, to start at the basics, there are two fundamental responses that all types of life (that are capable of detecting photons) have in response to light – they either respond positively to it and move towards the source (positive phototaxis) or negatively and flee from it (negative phototaxis). Lepidopterists are known to be the former, which explains why they converge on sources of light (such as bulbs). 

And while this appears to make sense so far, it is actually confusing to many scientists – why would an insect that is vulnerable to predators move towards a light source and make itself more visible? In fact, logic suggests that moths should actually show negative phototaxis and head towards the darkest areas they can find – they do have drab colours for camouflage afterall! 

However, the idea that lepidopterists use light for navigation helps to explain this and gives a plausible reason why they are in fact attracted by ambiance rather than repelled by it. The idea is simple and suggests that lepidopterists use the brightness of the lights in the sky (i.e. the sun, stars and moon) to calculate how high they are flying and use the angles that these lights hit their eyes to determine their direction. Thus, they think that because the lights are getting brighter, they are actually getting higher in the sky (which generally makes them safer from many of their predators, such as spiders, which live amidst foliage). 

So although this might seem like a bizarre explanation for why moths are attracted to light, remember that moths have evolved over millions of years in an environment where the brightness of the night sky has scarcely changed. It is only recently that humans have invented and built all of these streetlights and exterior lamps that are confusing them! Essentially, all the light we produce at night is hijacking their complex and highly evolved navigating systems because they now get much close to sources of light than they are expecting to! 

This concept also explains why moths end up spiralling round bulbs for hours at a time and, basically, because the stars and the moon are so far away from us, their light hits moth eyes in parallel to the horizontal axis of flight. Thus, moths have evolved a system where they use the information that this light provides to work out whether they are turning or travelling in a straight line. (Think of a cross where the flat line represents direction and the vertical one represents height).

This system is actually fairly simple and works well, until of course they become too close to a light. Once this happens, the angle the light strikes the eye at is steep enough to make the insect think that it is turning so it constantly has to compensate and turn itself to ‘return’ back to a straight line of flight. Thus, while we can see that the moth is actually flying in circles around the light, the disorientated moth thinks that it is flying in a straight line! 

And if this isn’t enough for the poor moths to contend with, many lepidopterists also believe that because moths are nocturnal (sleep during the day), being close to such a bright light actually makes them sleepy. When this happens, they are believed to enter a ‘rest mode’ and attempt to sleep, which is why they often try to land on (or nearby) the light – making it even harder for them to escape its clutches!