It was a hilarious and fun year in zoology (the study of animals). We saw penises that sting, some very bright birds making nests out of anti-bird spikes, and a genetically modified caterpillar with spider superpowers (yes… very Marvel Universe, I know). Here are my favourite five (with citations):
#5: A male wasp uses its penis as a stinger.
Yeah, that’s right. Two sharp spines stick out of his tip. Normally it’s the female wasps that sting, and their stingers are technically a piece of sexual anatomy, too. The ovipositor is a long organ out the back end of a wasp used to lay eggs, and in some wasps/ants/bees it’s modified into a venom-containing stinger. If you’ve ever been stung, it was a female, and she used her modified ovipositor to do it. Males normally don’t have stingers, but a Japanese researcher was feeding male mason wasps (Anterhynchium gibbifrons) to his frogs and was surprised that the frogs kept spitting them out. Careful investigation revealed the male wasps were stabbing the frogs with their spiky penises. Around 35% of the time, frogs spit out the stinging wasps (65% of the time they ate them anyway), but when the wasps’ penises were ripped off, males got eaten every time. There’s apparently no venom associated with the penis stinger, which is interesting, I think. Researchers think there may be more examples of this phenomenon to be seen in nature. You might be glad to know they do not appear to use the stinging spines when mating, so they aren’t used to hurt females. Just predators. Here’s video.
- Sugiura, S., & Tsujii, M. (2022). Male wasp genitalia as an anti-predator defense. Current Biology, 32(24), R1336–R1337. https://doi.org/10.1016/j.cub.2022.11.030
#4: Solar storms scramble bird brains
We think about solar wind causing Northern Lights, or messing up satellites, but we rarely think about how it affects animals, and I don’t think I’ve ever seen a paper suggesting animals have evolved in response to it. But here’s a study that merges zoology and astronomy. It’s nerd heaven.
In Jan 2022, a giant Steller’s Sea Eagle turned up near Providence RI. These things don’t even live in North America, and they can be even bigger than Bald Eagles. Birders lost their minds. When birds turn up in the wrong place like that, they’re called “vagrants” or “accidentals.” One of my favourite 2023 science stories put forth a new hypothesis about why accidentals happen: Maybe solar wind messes with the magnetic senses that power their orientation abilities. Researchers looked through two million captures of 152 land-bird species in North America over 60 years, and found, as expected, that when the Earth’s magnetic field was out of whack (“disrupted”), more birds ended up in the wrong place! Cool!
And there’s an interesting second finding: The sun goes through 11-year cycles of activity. When the 11-year solar cycle peaks – when there’s a peak in magnetic field disruptions – vagrancy happens less. They hypothesize that during the peaks of those solar cycles there’s so much electromagnetic noise that birds just ignore magnetic fields. But when the solar cycle is at a minimum, and there’s less noise, birds trust their magnetic senses more, making them vulnerable to mistakes.
- Tonelli, B. A., Youngflesh, C., & Tingley, M. W. (2023). Geomagnetic disturbance associated with increased vagrancy in migratory landbirds. Scientific Reports, 13(1), 414–414. https://doi.org/10.1038/s41598-022-26586-0
#3 How vampire bats evolved their taste for blood.
I’m especially psyched about this paper because it’s one I wrote with my bat buddy Gerry Carter! Vampire bats are the only mammals that drink blood. We wanted to understand how the habit of blood-feeding (also called sanguivory) evolved. We came at it from two angles at once: by figuring out what their ancestors fed upon (before sanguivory), and by looking at all the other instances of blood feeding among mammals.
It turns out blood-feeding – although rare in mammals – is not actually rare at all. There are at least 61,000 species of blood-feeding insects! Sanguivory has evolved at least 25 times among animals! We made the first exhaustive list of all the blood feeders. It includes vampire bats, seven different groups of birds, lampreys, some catfishes, vampire moths, some beetles, six different groups of flies, fleas, three kinds of bugs, ticks, mites, copepods, isopods, leeches, and a snail. One of my favourites in the list was a tiny midge that feeds off of mosquitoes that have fed on blood themselves!
We concluded that the evolutionary story for vampire bats goes like this: Blood-feeding evolved in an insectivorous ancestor to vampire bats, and that it happened one of two ways: One possibility is that the insect-eating ancestors of vampire bats fed on ticks and biting flies and other things that are common at open wounds, eventually feeding on the blood directly. The other is that the bats started feeding on open wounds, just like many birds do today.
We rejected a few other possibilities, like a fruit-eating ancestor, or a nectar-feeding ancestor. It was also fun to publish with Gerry because he and I have been working on bats together since I was a grad student and he was an undergrad at Cornell. He’s become a global superstar in the world of bat biology, but I was there when he learned how to catch bats with mist nets. Working with him honestly feeds my soul.
- Riskin, D. K., & Carter, G. G. (2023). The evolution of sanguivory in vampire bats: origins and convergences. Canadian Journal of Zoology, 101(4), 207–221. https://doi.org/10.1139/cjz-2022-0115
#2 Silkworms with Spider DNA Spin Tougher-than-Kevlar Silk
Spider silk is six times stronger than kevlar, but still lightweight and flexible. It’s also biodegradable. So spider silk would be a great material for clothing and for manufacturing. But getting spiders to mass-produce their silk for commercial purposes has been basically impossible. They don’t make very much web, and if you put them in a container together they eat one another. Not ideal.
Silkworms do make silk in large quantities. Silkworms aren’t actually worms. They’re caterpillars that spin their fluffy cocoons out of one long strand of silk. Over more than 4,000 years they’ve been bred by humans so we can harvest that silk. Now, researchers in China have used CRISPR-Cas9 technology to put spider DNA into the silkworms, so that instead of making silkworm silk, they make spider silk. The silk their genetically modified silkworms made
Forget the bullet-proof vest implications, if we could simply be replaying (plastics-based) rayon with this new biodegradable material in the clothing industry, it could have a huge impact on plastic pollution around the world. It’s also possible the silk would be helpful for surgical sutures, and other applications we haven’t even dreamed up yet!
- Mi, J., Zhou, Y., Ma, S., Zhou, X., Xu, S., Yang, Y., Sun, Y., Xia, Q., Zhu, H., Wang, S., Tian, L., & Meng, Q. (2023). High-strength and ultra-tough whole spider silk fibers spun from transgenic silkworms. Matter, 6(10), 3661–3683. https://doi.org/10.1016/j.matt.2023.08.013
#1 Birds make nests out of spikes designed for the sole purpose of repelling birds.
Ornithologists stumbled upon four examples of these unusual bird nests – one in Antwerp, Belgium, one in Rotterdam, Netherlands, one in Enschede Netherlands, and one in Glasgow, Scotland. All four were built entirely out of long metal strips of anti-bird spikes. One of the four nests (Rotterdam) was made by crows. The other three were by magpies.
A magpie nest constructed with anti-bird spikes, removed from a sugar maple tree in Antwerp, Belgium. The spikes at right are shown in their more typical arrangement, sticking up out of buildings to prevent birds from landing there. Photos by Auke-Florian Hiemstra.
This isn’t the first time birds have done something like this. Birds make nests out of all kinds of junk. In fact, a recent review of tens of thousands of nests — built by 176 different bird species, on every continent except for Antarctica —found that the nests contained artificial materials, including plastic bags, cloth straps, fishing line, paper towels, dental floss, rubber bands, condoms, and cigarette butts.
This bird-spike story is different, though, in that the birds aren’t finding this stuff on the ground this time. They’re ripping it off buildings to use for their nests – and the stuff they’re using is designed specifically to stop them from nesting. They’ve outsmarted us.
- Hiemstra, A.F., Moeliker, C.W., Gravendeel, B., & Schilthuizen, M. (2023). Bird nests made from anti-bird spikes. Deinsea 21: 17–25. https://www.hetnatuurhistorisch.nl/fileadmin/user_upload/documents-nmr/Publicaties/Deinsea/Deinsea_21/Deinsea_21_17_25_2023_Hiemstra_et_al.pdf
A Final Thought
To me, these five stories epitomize what makes biology so special: it’s a way to explore the world in ways no one has before.
