Sweet secretions under stridulating wings.

A male and female Hawaiian tree cricket (Prognathogryllus spp.) copulating in the ‘ohi’a canopy.

On a cloudless October night in the Alaka’i wilderness of Kaua’i, along the southern pali lining Wainiha valley, a chorus of tree crickets rings over my head.

Prognathogryllus is a genus of tree crickets (subfamily Oecanthinae) endemic to the Hawaiian Islands. They are heard stridulating throughout the night yet are seldom seen, as they exist high in the trees. That’s where they get the name tree crickets, I assume.

Stridulation is one of my all-time favorite words. It is the term used to describe the process in which animals produce sounds by qucikly rubbing certain body parts together. Well-known stridulators include cicadas, beetles, grasshoppers, and of course, crickets. In the case of Prognathogryllus, the body parts being rubbed together are the stiff wings of the male crickets, which contain several microscopic teeth that, when rubbed together, produce the song. The goal of the song is to attract a mate. Different species of tree crickets produce different songs, some chirp and some trill. Prognathogryllus are trillers.

I walk along the mossy earth looking up, my headlamp beaming. The crown shyness of the ‘ohi’a trees form river deltas of black night sky that sway in the wind. I follow the trills and try and get close. I try climbing lower trees to reach the singing insects, but as I get closer the trilling stops. I don’t think they like the light. I put out my headlamp. I wait for what feels like minutes but is likely only seconds until the male crickets begin singing again. I do what I can with no light to continue my approach until I feel close enough. On goes the headlamp, and off goes the cricket’s song. Where are they? I just can’t get high enough. Let’s try the next tree.

And the next tree and the next tree and, maybe the next tree.

I find an ‘ohi’a that was a bit easier to climb, thanks to its slanted trunk, and begin my ascent. I get quite close to a stridulating male and turn off my lamp. I awkwardly adjust my body to get a bit closer and wait until I hear him again. As soon as I do, I relight my lamp. Let there be light, and there was Prognathogryllus, right in front of my face, dangling from a thin manono (Kadua affinis) branch that neighbored the slanted ‘ohi’a. A pair mid-copulation, at that. I damn near fell off the slanted ‘ohi’a after a sharp gasp, I could hardly believe my eyes. After calming my breath, I took some photographs of this exciting observation, and would now like to tell you all I can about the picture below.

A male Prognathogryllus tree cricket clings onto a branch while a female clings onto him. Note the difference in the wings of the two, the males wings are more developed than those of the female. He rubbed his wings together rapidly to produce a gentle trill that attracted this female.

This picture is truly worth a thousand words, but I’ll try not to go on quite that long.

The male cricket is using his hooked feet to cling onto the branch while the female clings onto him. Notice how the female is face-deep underneath the males stridulatory instruments. She is feeding on sweet secretions from the males metanotal gland. This gland produces metanotal fluid which has a sole purpose of keeping the female around while the reproductive process is taking place. It is apparently quite delicious, although I cannot confirm. The copulatory process can go on for quite a while and the females can get bored. Along with secreting that sweet sweet juice, the males will also stridulate while the female is clung to him to keep her interested.

What takes so long, you ask? Well, the male has to transfer his precious gametes to the female in the form of a spermatophore. See that glowing white orb at the end of the females abdomen? That is the spermatophore. By the time I stumbled onto this pair, the male had already stabbed his wrapped up sperm package into the female. How romantic.

But the process is not over yet. The spermatophore takes some time to empty into the females reproductive system, and he has to keep her occupied while it does. He keeps her full on metanotal secretions and sweet stridulations until it fully drains. If he loses her attention, the female will simply remove and eat the spermatophore before the process is complete. The post-transfer metanotal feast can occur for over an hour!

I didn’t stay for quite that long.

Next, the males sperm will fertilize the females eggs. When they are ready to be laid, the female will inject her sword-like ovipositor into soft wood and lay her eggs. In a few months, tiny cricket nymphs will crawl out of their egg cases in the soft wood and go through 5 instar stages (which takes about 6 weeks) until they too can stridulate and lick metanotal glands and transfer spermatophores. Oh to be a cricket!

I learned all of this from this wonderful website: https://oecanthinae.com/, hosted by tree cricket expert Nancy Collins. I highly recommend checking it out if this little story has tickled your fancy. In 2022, Nancy blogged every single day for the whole year all about tree crickets. Here is the link to my iNaturalist observation for these lovely crickets: https://www.inaturalist.org/observations/246850069.

Truthfully, I didn’t know what I captured with these photos until I took a closer look. I guess the moral of the story is go out in the middle of the night, listen for crickets chirping and trilling, and climb up after them. Grab a male, lick the metanotal gland, and report back. I’m dying to know what all the fuss is about.