Yesterday, I was poking around a small bush of white flowers looking for insects to photograph. I noticed this butterfly hanging from the bottom of a flower, rather than sitting on top:
What are you doing under there?
I panned around to underneath the flower and found out why:
Unlucky butterfly.
The butterfly had been snared by an ambush bug (Phymatinae), which is a subgroup of assassin bugs (Reduviidae). I think the above animal is a nymph belonging to the genus Phymata. These bugs hang out underneath flower petals until unweary pollinators visit. They then lunge out and snare their prey with their enlarged raptorial appendages, piercing the exoskeleton with a syringe like rostrum.
Here is an adult of the same, or a similar, species. About one of every three flowers in this bush had an ambush bug laying in wait below.
Phymata sp
'Come a bit closer my pretties.'
If any insect-gurus can identify this exact species, it would be much appreciated.
The sunburst diving beetle, Thermonectus marmoratus, is an adept predator. As adults, these Dytiscid beetles are strong swimmers and prey on a variety of aquatic animals by tearing them to shreds with their powerful mandibles. They also spend some time out of water and can fly from one water supply to another. When it is time to reproduce, female diving beetles enter the water and lay eggs on the stems of aquatic plants and macroalgae. When the eggs hatch, the larvae (known commonly as water tigers) enter the water column and begin their rein of terror.
In the lab, these morphologically distinct diving beetle larvae are typically fed tadpoles or mosquito larvae. In the wild, however, they probably eat anything unlucky enough to get too close. When hunting, these beetle larvae either swim around actively or hang, with their tail touching the surface, just below the water line. When they spot a prey animal, they swim over and strike the target with their powerful mandibles (Watch a video of a predation event below). Unlike the adults, larval diving beetles gradually suck the fluids from their prey, resulting in an unfortunately slow demise.
The predatory nature of sunburst diving beetle larvae is highly dependent on their visual system; and boy is it a bizarre one. While the adults have typical arthropod compound eyes, the larvae see the world through stemmata. Stemmata, which are commonly seen in larval insects, are simple lens eyes that rely on superficially similar optical principles to vertebrate eyes. On each side of the head, the larvae have six stemmata as well as a lens-less eye patch (see below). Within each of these eyes there are two distinct retinas, one on top of another. In total, this means that these T. marmoratus larvae have fourteen eyes and twenty-eight distinct retinas!
Front and side views of the head of a T. marmoratus larva. E, eye; EP, eye patch; M, mandible. Adapted from Mandapaka et al., 2006 and Maksimovic et al., 2009.
This larval visual system has a befuddling number of bizarre optical properties. The retinas are sensitive to a broad range of wavelengths, including UV, and the photoreceptor architecture is suggestive of polarization detection. In addition, some of the lenses seem to have novel bifocal and chromatic aberration-correcting properties. Despite the research into all of these strange visual adaptations, the ecological significance of most of the eyes on this animal is completely unknown.
The best understood eyes in the diving beetle larva are E1 and E2. They are forward-looking and primarily used for predation. However, when you look at the main retina in these eyes, you surprisingly find that it is only composed of a thin horizontal band, two photoreceptors tall. Imagine trying to view the world in a thin strip, two pixels high! So, how is the diving beetle larva using these eyes to zero in on prey? Well, it turns out that these sort of strip eyes are not completely novel in nature. Jumping spiders, some copepods, and a pelagic snail all have strip retinas. In order to see the world, they scan their narrow retinas rapidly back and forth, as in the image below. Diving beetles, on the other hand, have absolutely no musculature to move their eyes or retinas. So how do they see?
Look again at the predation video from above. Notice that once the diving beetle larva spots the mosquito larva, it begins bobbing its entire head up and down. The diving beetle larva is scanning the mosquito with the strip retina in its main eyes. As it gets closer, the scanning movement actually becomes more pronounced, since the target takes up more of the field of view. This technique allows the diving beetle larva to accurately hone in on its prey without sacrificing limited head-space for a full retina or eye muscles.
The closer you examine arthropods, the weirder they seem to get. Who would have though that this small aquatic predator would have such a complex and fascinating visual system? In order to discover the most exciting aspects of living things, you need to look. That’s where science starts; with someone peering through the confounding subterfuge of nature, hoping to widen our glimpse of the gear-works within.
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The research discussed in this post is being carried out at Buschbeck lab at the U. of Cincinnati.
References:
Mandapaka K, Morgan RC, & Buschbeck EK (2006). Twenty-eight retinas but only twelve eyes: an anatomical analysis of the larval visual system of the diving beetle Thermonectus marmoratus (Coleoptera: Dytiscidae). The Journal of comparative neurology, 497 (2), 166-81 PMID: 16705677
Buschbeck EK, Sbita SJ, & Morgan RC (2007). Scanning behavior by larvae of the predacious diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae) enlarges visual field prior to prey capture. Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology, 193 (9), 973-82 PMID: 17639412
Put yourself in my place: You’re collecting mantis shrimp by cracking reef rubble on the beach of an island on the Great Barrier Reef (I know, there are worse ways to spend your day). You split one particular rock, and instead of shrimp, out pours a brood of arachnids. Not pycnogonids, not spider crabs… freaking spiders! Well, at this point, if you’re me, you shriek like a little girl and frantically crab-walk backwards while brushing yourself off.
In that embarrassing moment I had learned something new: There are arachnids that live, partially, in the ocean. These small Desid spiders live in intertidal rubble. During the day they hide in silk-sealed air chambers within the rubble. At low tide they come out to hunt stranded critters along the tide pools.
A marine spider, Desis martensi, on an out-of-water coral head. It has captured what looks like a pistol shrimp. Photo: Wild Singapore
PZ Myers, my original science blogging hero, was disturbed by the video I posted (gloatingly) of some Stomatopod on Cephalopod ass-whooping.
You know, the rotten little crunchy, jointed thing wouldn’t have stood a chance if he’d been fighting within his own weight-class. I found this video on a blog called Arthropoda — a clearly biased advocacy site for violence on molluscs by the world’s dominant, bullying metazoans. -PZ
OK, let’s give the squishy a size advantage over my favorite mantis shrimp, Hemisquilla californiensis.
Ha-Ha! Run for your life, softy!
Seriously though, I am very suspicious of that video. The octopus seems lethargic and completely uninterested in the mantis shrimp. I get the feeling that the filmmakers are constantly pushing the octopus back towards the burrow as it is trying to get away.
Regardless, the score is still:
Maybe this will make the Tentacled-One feel better though…
We don’t get to see for certain that the mantis shrimp in that photo gets eaten. Personally, I imagine a Rocky IV-style, final round recovery from the crustacean.
Check out this brutal video from Roy Caldwell’s Lab at UC Berkeley. It shows the ‘interaction’ between a mantis shrimp (Odotodactylus scyllarus) and a blue-ringed octopus (Hapalochlaena lunulata), when the latter is introduced into the mantis shrimp’s tank. Both of these animals occur amongst coral reef rubble in the Western Pacific, so it’s possible that they often meet in the wild. Take a look at what happens when they do…
Well, that didn’t go so well for the unfortunate octopus. Take that, squishies!
It’s unknown how the stomatopod copes with the venom of the blue-ring as it kills and devours the cephalopod.
You can learn more about keeping your own murderous mantis shrimp at Roy’s List.
Assassin bugs (Reduviidae) belong to the Hemipteran order, sometimes referred to as “true bugs.” Hemipterans also include aphids, leafhoppers, and cicadas. Like all Hemipterans, assassin bugs feed using a specialized proboscis, called a rostrum. However, unlike their vegetarian, sap-sucking cousins, assassins use their rostrum for extracting fluids from living prey.
Though most assassin bugs feed on other insects and arachnids, some species predate mammals such as bats (video) and humans. In fact, certain species of assassins are the primary vector of Chagas disease in humans. Assassin bugs are evolutionarily specialized for their predatory lifestyles in an astonishing number of ways:
Stylets and digestive venom: Integrated with the rostrum, assassin bugs have specialized serrated stylets for tearing into crevices in animal tissue. Once inside, the assassin injects a digestive saliva that breaks down the unlucky prey’s innards into a nutrient rich slurry; which the assassin then sucks back up through the stylet.
Raptorial forelegs: Thread-legged assassin bugs (Emesinae) have beefed-up forelegs equipped with sharp spines for grabbing, impaling, or pinning their prey. Liken this adaptation to the forelegs of praying mantids and “spearer” mantis shrimp.
The specialized foreleg of thread-legged assassin bugs (Redei, 2007; artour_a).
Sticky hairs: Assassin bugs of the genus Zelus also use their forelegs to capture prey. However, instead of sharp spines, they use fine hairs coated in a glue like substance. It is not known if the bugs produce their own glue, or if they obtain it from plant sap. Regardless, they use it to ambush and immobilize prey as they begin to liquidate their insides.
Zelus longipes has fine hairs (electron micrograph, right panel) on its forelegs which are coated with a viscous, glue-like material. This is used to immobilize prey. Click the image for a much larger version. (Photo by: Chuck Ulmer; SEM image adapted from Werner and Reid, 2001)
Lure signals: Feather-legged assassin bugs (Holoptilinae) lure ants to their doom with visual signals and pheromones produced in a special organ, called a trichome. Read more at Myrmician.
Wow, I really got sidetracked in that introduction. I had no idea how awesome assassin bugs were. Every bit of research I completed for this post led me to another exciting factoid.
Regardless, I need to get to the point of this post, which is a new paper about some disturbingly sinister predatory tactics in the assassin bug species, Stenolemus bituberus. This assassin bug has its work cut out for itself, as it predominately stalks some truly dangerous quarry, arachnids. The assassin bug faces the challenge of obtaining an advantageous position on the spider; from which it can launch a swift, fatal strike. The researchers found that these sneaky assassins use more than one technique to outsmart and turn the tables on their cunning prey.
The Australian based researchers placed assassin bugs on the webs of five species of spider. Through tedious observation they discovered that S. bituberus uses two contrasting methods to get the drop on web-building spiders. Both methods involve manipulation of the spider’s own web.
First, in a stalking behavior, the assassin sneaks up on the spider. In order to accomplish this, the bug walks over the web with an irregular pattern of footsteps. The spider does not notice arrhythmic motions, and the assassin is able to get within striking distance. This technique is also used by web-invading jumping spiders (and is useful when you want to avoid drawing the attention of colossal sandworms while crossing the deserts of Arrakis). In addition, the assassin bugs also make use of natural “smokescreens” such as strong gusts of wind on the webs in order to advance on the unwitting spiders.
The researchers also noted a second predatory behavior in which the assassin bugs bait and lure the spiders. They accomplish this by plucking the web in such a way as to mimic the struggles of a helplessly trapped insect. When the spider comes over to inspect and process its captive, it instead gets an carapace-full of rostrum, as the assassin bug pounces it. Also, considering the ant-luring techniques of the feather-legged assassins described above, one must wonder if chemical attractants are involved in this case as well. Watch a video of the luring and striking behavior, here.
As an interesting aside, the researchers also noted that the assassin bugs habitually tapped the spiders with their antenna just prior to the strike. This behavior is seen in other predatory arthropods, however its purpose is not clear. It is possible that the assassin bug is getting last-second distance, orientation, and identity information about the spider before launching its attack. Another possibility is that the assassin bug is hypnotizing the spider, habituating it to stimuli, so that it is less likely to respond violently when the assassin strikes for real.
Damn, these bugs are awesome.
References:
Wignall, A., & Taylor, P. 2010. Predatory behaviour of an araneophagic assassin bug. Journal of Ethology. DOI: 10.1007/s10164-009-0202-8
Wolf, K., & Reid, W. 2001 Surface Morphology of Legs in the Assassin Bug (Hemiptera: Reduviidae): A Scanning Electron Microscopy Study with an Emphasis on Hairs and Pores. Annals of the Entomological Society of America, 94(3), 457-461. DOI: 10.1603/0013-8746(2001)094[0457:SMOLIT]2.0.CO;2
Redei, D. 2007. New and little-known thread-legged assassin bugs from Australia and New Guinea (Heteroptera: Reduviidae: Emesinae). Acta Zoologica Academiae Scientiarum Hungaricae. 53 (4), 363–379.
Stomatopods, or mantis shrimp, are an exceptional order of marine crustaceans made up of over 500 species that live in a variety of benthic habitats around the world. They are aggressive predators that actively seek out their prey with an advanced suite visual and chemosensory organs. Stomatopods are immediately distinguished by a pair of enlarged raptorial appendages located ventrally, near their heads. Stomatopods use these appendages as their primary means of predation, as well as for digging in substrate, defense, and intraspecific sparring.
The appearance of the raptorial appendages varies from species to species as they are evolutionarily specialized for capturing or killing distinct prey animals. The raptorial appendages can be deployed at lightning speeds, and with tremendous force relative to the size of the stomatopods; which can range from under 2 cm to 40 cm body length. Depending on the species, these appendages can be employed to smash, spear, or grab their prey.
Here are video examples of “smasher” and “sprearer” stomatopods in action:
Odontodactylus scyllarus smashes the shells of mollusks and crustaceans.
Lysiosquillina maculata ambushes swimming fish and crustaceans, spearing them out of the water column. Click through to Youtube to see this one.
Since the 1960’s, a series of research has unraveled the speed, power, and mechanics of the stomatopod’s astonishing attack.
Arthropoda 
