Animal Form and Function 6: Insects

And then we arrive at the insects.

My university has a very limited array of specialized high-level zoology courses.  There are no high-level electives about the intricacies of lampshells or even mollusks at the University of Ottawa.  There are courses about various groups of vertebrates, and about unusual microbes like the microsporidia that get a lot of attention for other reasons.  We do have an entomology course, because insects are that fundamental and that numerous.

Humans talk a mean game about being the dominant organism on planet Earth, and it’s not an unreasonable assertion.  Humans are on a short list of species found on all continents (no matter how those continents are parsed) and most of the other contenders are animals like cattle whose ecology is intimately entangled with ours.  If we compare humans (or even primates at large, to be honest) with insects, though…there are millions of them for every one of us, and they are omnipresent.  Insects are defining features of every ecology except for the oceans, and a few visit even there.  As noted earlier, the insects have more species to their name than any other taxonomically similar group of organisms.

So it’s no surprise that some very interesting beasties lurk in this massive assemblage.

The primary activity in the insect lab is a classification exercise.  The students have a set of preserved insects and an elaborate online taxonomic key.  Their goal is to examine the specimens’ anatomy and figure out what insect order claims each of them.  This exercise is a bit obscure for many of them, as few students have a mental box for the Hemiptera or Diptera to make learning what is or isn’t in those orders an exciting surprise.

There is, however, one chunk of that exercise that always, always gets their attention, and that is the dobsonfly.

 

Dobsonflies are, as the course tells it, part of the Neuroptera, a widespread but obscure order of insects.  (The order was recently split, creating a Megaloptera for the dobsonflies and their kin.)  They’re named for the structure of their wings, which feature an unusually high density of veins.  Dobsonflies are, like a lot of animals I’ll be showcasing, imposing but harmless.  Adult males develop massive mandibles used for mating and territory displays.  The pincers, like a fiddler crab’s claws, are so huge that they are useless for anything other than these displays.  And unlike many of the bizarre animals this course presents, dobsonflies are found all over North America’s riparian regions, so a dedicated observer won’t have to travel far to potentially see one.

The Neuroptera proper have an even more exciting representative in the famous ant lion.

The ant lion is best known for its larval form, a rotund insect with huge jaws that digs burrows in sandy soil.  The burrow’s shape keeps the sand at its critical angle of repose, the steepest angle the sand can maintain without collapsing.  So, when an unsuspecting ant wanders into the burrow, it immediately begins tumbling downward toward the center, unable to gain purchase on the rapidly collapsing burrow walls.  To add a little certainty, many ant lions throw sand at such prey until it falls to the bottom, at which point they seize and consume.

And yes, the ant lion is basically a real-world Sarlaac pit.

Speaking of unusual diets, this is the rhinoceros spear-bearer, Copiphora rhinoceros.

The Orthoptera encompass grasshoppers, crickets, and a huge assortment of “katydids” and “bush crickets” of various affinities.  While primarily herbivores, their mouthparts are quite generalized, and many orthopterans have taken up variant diets.  The rhinoceros spear-bearer is one of the most striking of these deviants, preying on plant seeds and other katydids alike.  It’s also aggressive and spiny, and quite capable of injuring incautious handlers.

It’s still not as imposing as the New Zealand weta crickets.

New Zealand has a seriously weird ecology, including carnivorous parrots and throwbacks to the Triassic period.  One of New Zealand’s most distinctive creatures is the weta, a group of enormous crickets that have evolved into the niche that, in much of the rest of the world, is occupied by shrews and other small insectivorous mammals.  Wetas are aggressive, predatory crickets the size of baseballs (they get way bigger than the one in the video) that have turned the spiny jumping legs of the cricket into defensive weapons in addition to growing big, pointy mandibles.  That cat doesn’t know what it’s up against.

Speaking of giant predatory insects, here is the giant Japanese hornet I mentioned earlier.

This monster is, like most hornets, a very social wasp.  It’s also the size of a large-handed person’s thumb, vomits caustic stomach fluid as well as stinging, and specializes in eating honeybees.  And it’s not from distant mountainous parts of Japan, but can be found in downtown Tokyo.  Small numbers of them can attack a honeybee hive, dismember and discard thousands of honeybees each, and gorge themselves on the eggs and larvae hidden inside the hive.  But the bees are not defenseless.  If the bees can isolate individual hornets inside the hive, they swarm them.  They do not try to sting, as they cannot penetrate the hornets’ armor.  Their goal is for their huddled, vibrating masses to raise the temperature around the hornets, because honeybees can take slightly warmer locales than the hornets, and can induce heatstroke in their attackers if they have enough time.  These bees did not.

Neither did this mantis.

There is a common misconception about mantises and spiders that requires correcting.  It’s a bit of conventional wisdom that mantises, tarantulas, black widows, and all manner of other charming arthropods have coitus that ends with the male being killed and eaten by his paramour.  As the video above shows, this does happen occasionally, but it is not standard practice.  Arthropods have a sensor-heavy nervous paradigm that relies on collecting enormous amounts of information but, generally, processing it fairly simply.  Male arthropods, in particular mantises and spiders, are usually much smaller than females, which is a problem for them, as their neural programming assumes anything smaller than them is either food or scenery.  Males have to undertake specific mating displays to convince females not to eat them, mate, and leave while she’s still pacified by that display.  If he lingers too long, or if the pair is interrupted vigorously enough that she stops being distracted, she’ll revert to her natural instincts regarding smaller animals near her, and that’s the end of him.  A starved female is decidedly easier to distract.  So, chances are the above cannibalism is a show that the mantises put on for the camera.  Notably, thanks to insects’ various thoracic ganglia, a decapitated male continues to mate.

After all of that creepy-crawly grotesquery, my students and my readers usually need a break…so here’s a short video of someone’s pet Goliath beetle eating baby food out of a spoon.

Watch that a few times before watching this next video.

There are a lot of videos of centipedes eating surprising animals, but this one is probably the most intense.  Centipedes aren’t insects, but the old classification scheme assumed a close affinity between the two groups thanks to their mouthparts, so they come here in the class sequence.  And this one, the size of someone’s forearm, fills its guts by climbing to the top of a cave and waiting for a bat to fly into it, at which point it seizes the bat, injects it with venom from its huge maxillipeds, and eats it right there, as it doesn’t have the strength or agility to drag its prize anywhere.

While we’re here, my students usually remember a certain animal they’ve come across and become suddenly curious about it during this lab, so this animal is a house centipede, genus Scutigera.

House centipedes freak people out because of their size (up to several centimeters), numerous long legs, and impressive speed.  Fortunately for us, they are nocturnal and predatory, particularly liking silverfish, cockroaches, and bedbugs, so we hardly ever have to look at them and they get rid of far more problematic arthropods on our behalf.  Little wonder the Japanese keep them as pets.

 

Not all centipede hunts go as well as this one or the bat hunt, though.  Some centipedes bite off a little more than they can chew.

This scolopendrid centipede has made the mistake of tangling with the grasshopper mouse, a rodent in the American southwest that is one of the region’s primary insect predators.  The grasshopper mouse knows exactly what to do to keep its brood of babies safe…jump to dodge the centipedes sharpened tail and venomous head, and mangle both ends until it mostly stops moving, and then eat.

So…that’s heartwarming, I suppose?

Here’s the Goliath beetle video again.  There, that’s better.

(Also, a bunch of these images come from www.thesmallermajority.com, the photoblog of Piotr Naskrecki, author of a fantastic book by the same name.  I highly recommend it.)

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