bugsicles

backyard bug-inspired learning

[bugsicles]

Spooky Season Special: The Spitting Spider

In honor of the month of October, a post about one of the creepiest crawlies I've crossed paths with thus far

First off is a spider with a giant pumpkin head and jack-o-lantern face: the spitting spider (Family: Scytodidae).

This unique spider goes about catching prey in an unusual way - instead of constructing a web spun with silk from the spinnerets on its abdomen and waiting for a catch, it roams for its favorite food - other spiders - and once within firing range it shoots a gluey, silky net from its mouth to pin the prospective meal to the ground. It then proceeds to envenomate the restrained victim and wrap it with spinneret silk in more typical spider fashion. Their web-like spit projections, enlarged heads, and unusual eye arrangement distinguish these prowling night-time hunters. And given that they enjoy indoor living and are common in the U.S., there's a pretty good chance that one is haunting your household as we speak.

Figure 18.1, Suter & Stratton (2013)

In a way these spiders have re-invented silk, for while they produce conventional spider's silk in their abdomen, they also figured out how to make a functionally similar substance in their mouths. The friend in the photographs above has such a rotund 'head' precisely because of its saliva-generating needs. The cephalothorax houses the enlarged spit glands, which feed through the chelicerae (the two mustache-like appendages in front of the mouth), at the end of which sit the fangs (see below). Some of these glands produce venom, and some produce the fibrous net material and sticky substance that is squirted from the fangs when attacking prey (or attempting to dissuade a predator with a web pie to the face). Whether the net is laced with venom seems to be up for debate in the literature. Streams from the 2 fangs make an alternating zig-zag pattern, and this woven mesh contracts after it is fired, often pinning the quarry's legs to its body, in addition to binding the creature to the floor.

Chelicerae (a) and fangs (b) of a spitting spider (Figure 18.4, Suter and Stratton 2013).

It takes the spitting spider ~20 milliseconds to generate ~2 feet of silky string, oscillating its fangs at ~1000 wiggles per second to weave its net in midair. And it looks as cool as you would hope it would - videos from the first author of a great book chapter I found, from which much of this information is sourced, can be found here. The chapter, "Predation by Spitting Spiders: Elaborate Venom Gland, Intricate Delivery System" by Robert Suter & Gail Stratton, is very accessible and contains lots more awesome information about these spiders (read here).

Videos by Robert Suter

According to the authors, muscle-driven oscillations greater than ~500 cycles per second are rare in nature, given the time it takes for muscles to relax between contractions. So it seems unlikely that the spider is able to wiggle its chelicerae so fast on its own. Higher frequencies are possible when things other than muscles are driving the cycles, and in this case the authors suspect that the fang-silk system is behaving the way a water hose does when turned up all the way with its end free to lash around. The silk-glue is forced out of the fangs so fast that they jiggle in response, with a frequency determined by their mass and the elasticity of the connective tissue of the chelicerae. The relatively small fangs of this spider may be that way since they allow quicker oscillations for a more tightly woven mesh trap (though the authors note some conflicting evidence, including the fact that the larger fangs of some species in the group do not appear to wiggle more slowly than others). Regardless, this is all I'm going to think about when I use a hose now.

I had never heard of spitting spiders before coming across this individual in my home the other night, and I suspect the same is true for most people, which is surprising given how common and rad they are. There doesn't seem to be any end to the fascinating goings-on right under foot!

Sources:

Suter, Robert & Stratton, Gail. (2013). Predation by Spitting Spiders: Elaborate Venom Gland, Intricate Delivery System. 10.1007/978-3-642-33989-9_18. https://www.researchgate.net/publication/268069024_Predation_by_Spitting_Spiders_Elaborate_Venom_Gland_Intricate_Delivery_System

Spider. Encyclopaedia Britannica. https://www.britannica.com/animal/spider-arachnid

bugsicles is a blog about the bugs I find in my backyard in southern New Mexico. I don't use any special equipment beyond a cheap jeweler's loupe and a phone camera, and occasionally an amateur microscope.

[bugsicles]

ear of the katydid

(3rd post in the series)

As much as I have gotten into bugs lately, I never really thought about how they hear, or the fine details of how we humans hear, for that matter. Then, when I didn’t think my katydid could be any cooler, I come to learn that his are some of the smallest animal ears known, they are in his legs, and their structure and function is amazingly similar ours. This means that independently, and starting with different raw materials, they have solved the same problem in essentially the same way - an example of convergent evolution. Often times very different creatures come upon similar solutions to common 'problems' - how to move, how to see, how to hear, etc. It's easy to see how an animal would benefit from being able to detect sound in its environment, but the last common ancestor of all animals did not have this ability, meaning that hearing has evolved multiple times in the animal kingdom (and more than once in insects alone!). In the case of katydids and mammals, it's almost as if someone stole the other team's playbook. 

A three-step process

Both our ears and the katydid's have an outer membrane which vibrates in response to sound waves. On the other side of this membrane is a space of air, across which a rigid lever transmits and amplifies the vibrations of the membrane to a fluid-filled chamber. The flexible walls of this chamber resonate with different frequencies in different places due to its varying stiffness, and move hair-like structures positioned along its length, causing them to brush against a ceiling overhead. In this way, the location and intensity of the movement of the hairs in response to sound causes ion channels to open and a signal to propagate to the nervous system, containing information about the sound's loudness and frequency content. So, (1) flexible exterior membrane, (2) air chamber with a simple lever mechanism, (3) fluid chamber with hair structures, all present and performing the same function in both creatures, only about 20 times smaller in the case of the katydid.

Source: Montealegre-Z, F. et al."Convergent Evolution Between Insect and Mammalian Audition". Science, 16 Nov 2012.

The outer, middle, and inner ear

We call the outer membrane the eardrum (I am ignoring our wrinkly flesh flaps and ear canal, or the outer ear, since of course katydids don't have those). The air space with the connecting lever is the middle ear, with three tiny bones making up the lever in our case, and the air space connected to the back of our throat via the eustachian tube. This connection to the outside ensures that the air pressure on either side of the sealed membrane is the same (we are all familiar with the discomfort that comes when these two pressures do not match, as when driving over a mountain). In katydids, this air space is connected to the outside via one of their many spiracles or breathing holes, through which oxygen passively makes its way into their tissues. The essential task of the lever in both systems is to solve the change-of-medium problem. Sound waves in air carry a relatively small amount of energy, not enough to do much with from a noise detection perspective (unless the sound is very loud). Waves in a liquid can do more work, like move tiny fibrous structures that act like switches - such mechanoreceptors are common in the biology of many creatures. However, without intervention, very little of the energy of a sound wave in air is transmitted to a fluid (there exists an “impedance mismatch”). Since the fluid is far more dense, most of the energy is reflected. This is why, if you are underwater, you are hard pressed to hear someone at the surface trying to get your attention. In our ears, and in my katydid's, the weak sound waves in air strike a large surface area, and their collective energy is converted to the back-and-forth motion of the eardrum. These large vibrations are translated by the lever into smaller but more forceful pulses at its other end, allowing it to strike the fluid chamber (a.k.a the cochlea) with enough force to make a detectable wave in the liquid. The cochlea is part of the inner ear, and is where sound is processed. In katydids, it is a long tapering tube; in humans, it is as if this tube has been rolled into a spiral. In both cases, the vibrations of liquid in the tube are detected by thin fibers which relay the signal to the nervous system. Boom, roasted.

Notes

My primary source (below) is a paper studying the ears of a rainforest katydid; I am simply assuming there are no important differences in the hearing organ of this katydid and my own Greater Angle Wing.  Here I’ve posted pictures of my katydid, as well as the ears of a baby bird (conveniently free of feathers) and my two favorite lizards, since you can see their ear drums directly. If you could look down your own ear canal, you would see something similar. There are some small differences between a reptile's and a mammal's ear, but apparently the katydid ear design bears more resemblance to the mammal's.

It appears that the katydid ear is sensitive to a larger range of frequencies than is required for them to simply hear other katydids. So not only can they detect the calls of their own kind, they likely are listening for prey (in the case of carnivorous katydids) and predators (such as bat sonar). Given that they have one ear on each front leg, it seems probable that they have some perception of the directionality of sound as well. Bangarang.

References

Montealegre-Z, F. et al. "Convergent Evolution Between Insect and Mammalian Audition" Science, 16 Nov 2012. https://science.sciencemag.org/content/338/6109/968.abstract

https://science.sciencemag.org/content/338/6109/894.summary

https://knowablemagazine.org/article/living-world/2018/how-do-insects-hear

bugsicles is a blog about the bugs I find in my backyard in southern New Mexico. I don’t use any special equipment beyond a cheap jeweler’s loupe and a phone camera, and occasionally an amateur microscope.

[bugsicles]

song of the katydid

(2nd post in the series)

There are relatively few ‘singing’ insects - crickets, grasshoppers, katydids, and cicadas are perhaps so well known because they draw our attention with the sounds they make, which in most cases are intended to attract a mate. As soon as he came to live with us, our katydid was gracious enough to click for us every evening and throughout the night.

Grasshoppers, crickets, and katydids make their songs by rubbing a ‘scraper’ against a ridged surface called a ‘file’. In most cases, these structures are on their wings. Like most insects, my katydid has four wings - two front wings, which in his case are green and stunning leaf mimics, and underneath are folded two translucent hind wings. His ‘left’ wing overlaps the right on his back, and the file structure is on the underside of this wing surface, as seen in the photos below.

In the following video you can see that, in order to make his clicks, he quickly separates his wings, and as he allows them to relax bit by bit, the file slides past the scraper and the noise is produced. To the best of my knowledge, the clicks he is making are those meant to attract a female (these are the same sounds we heard on a nightly basis from his outdoor brethren). He may also be capable of making a loud protest click, as some katydids are, which those nearby may take as a warning that danger is near (my next post is about katydid hearing - prepare to have your mind blown). Apparently in some species males click in unison to amplify their signal. 

This particular way of producing sound is called stridulation, and can be achieved using various parts of the body - I believe the grasshoppers, crickets, and katydids that do make noise all use this method. Cicadas, on the other hand, go about things differently. They possess organs called tymbals, which have rigid ribs that make a sound when they relax after being flexed. By rapidly and repeatedly contracting and relaxing the muscles that deform the tymbals, they are capable of making a very loud call. My phone’s microphone couldn’t even handle the sound produced by the male scrub cicada below (genus Diceroprocta, species perhaps is cinctifera). I happened to have found a dead individual of the same species, which is where the still photos came from. Unfortunately I do not think the tymbals are outwardly visible on this species; I think they are located behind the distinctive flaps on his sides.

I am looking forward to summer nights abuzz with insectian conversation, and hearing our katydid’s clicks once again - though he is no longer with us, it is comforting to know that his song lives on.

References

Triplehorn, Charles A, Norman F. Johnson, and Donald J. Borror. Borror and Delong's Introduction to the Study of Insects. Belmont, CA: Thompson Brooks/Cole, 2005. Print.

bugsicles is a blog about the bugs I find in my backyard in southern New Mexico. I don’t use any special equipment beyond a cheap jeweler’s loupe and a phone camera, and occasionally an amateur microscope. 

[bugsicles]

portrait of a katydid

(1st post in a series)

Last August, we came across a Greater Angle Wing katydid in the yard. He was on the ground, and missing one leg. We took his condition to be a precarious one, so I brought him inside and placed him in an enclosure, thinking that at the very least I could get him hydrated and perhaps fed if I could figure out what he liked to eat. If not, I would put him high up in the same tree (where we had heard katydids clicking every night) and hope for the best. 

Nearby, I found leaves that something had obviously been chewing on, and he munched on those. Oak leaves and kale were also accepted fare, and he took a serious shine to blueberries (he would mostly scalp the skin off of them). He did not seem to react to my hands being nearby with wariness or fear, and I became accustomed to taking him out and holding some kale for him to nibble on every morning as he sat on my hand. Being a male, his clicks put us to sleep every night, and we soon came to rely on his friendly and benign presence.

As months went by, and the katydids could no longer be heard in the trees outside, our boy kept up his clicks through the winter. He began to outwear his chitinous exterior as his feet became less ‘sticky’, and he lost a bit of one antenna. I had hoped that his protected lifetime might far exceed his natural one, but at least in this case we weren’t so lucky - one evening in January he appeared subdued, and he died later that night. 

We still think about and miss him. He inspired me to learn more about insects and how they operate, and that is what the next few posts will be about.

bugsicles is a blog about the bugs I find in my backyard in southern New Mexico. I don’t use any special equipment beyond a cheap jeweler’s loupe and a phone camera, and occasionally an amateur microscope.

[bugsicles]

how to love a bug

I had never cared for or paid attention to bugs until I started looking at things in the backyard with a magnifier. Our pet lizard loves to spend time outdoors, and sometimes there is nothing to do but idly sit in the grass next to him as he basks in the sun. In such a situation you can’t help but notice that the greenery is teeming with activity, with strange creatures and mysterious structures around every corner. 

Strapping a jeweler’s loupe to my phone’s camera really opened up this little world, hidden in plain sight, and I started spending lots of time outside (with a lizard on my shoulder of course), taking photos and videos and recording the species I saw on iNaturalist. Watching an insect go about their daily life, in heightened detail, with your face inches away, is a very intimate experience, and you begin to appreciate them as individuals and as beings similar to yourself. The great thing about bugs as a vector for science education is how accessible they are, as they can be found nearly anywhere, and can usually be observed without the need for specialized equipment. For me, fortunate enough to have both a lovely green space to explore and an internet connection, they are a constant inspiration to learn about biology and physics and more. 

The first insect I ever fell in love with, and whose story I felt I had to share, was the first one I ever took home with me. I had learned about the ladybug life cycle after observing eggs, larvae, pupae, and adults in the pecan trees nearby. One day I decided to take a pupa inside simply to watch the adult beetle emerge. It just so happened that it was a less-than-common species (in my area, anyways) with a very uncommon spot pattern that I have not personally seen since. My partner named this gleaming ladybug Champlagne, and he changed the way I look at insects forever: