I believe it was Imhotep in 1999's The Mummy who said "Death is only the beginning...", and he was right! Not in the sense of returning from the realm of the dead to fight Brendan Fraser, but in the sense that death turns an organism's mortal shell into a entirely new sort of ecosystem. In this grisly-yet-surprisingly-positive episode, Nicole walks us through the science of decomposition, how it's applied to everything from solving crimes to food freshness, and why we couldn't live in a world without decay.

Nicole's Sources:

• LET THINGS ROT (the YouTube video Nicole was talking about): https://www.youtube.com/watch?v=PI_-eUOgqFI
• Australian Museum. 2025. Stages of decomposition. CW: pictures of decomposing pigs.
• Matuszewski, S. 2021. Post-Mortem Interval Estimation Based on Insect Evidence: Current Challenges. National Library of Medicine.
• Nowakowski, K. 2025. These beetles eat rotting flesh—and could unlock the next generation of antibiotics. National Geographic.
• Australia's Defining Moments: Digital Classroom. Can we solve the poo problem?

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Allan's Sources:

1. Coming soon!

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In this month's Filthy Animals, Rachel tests the strength of monogamous bonds in the animal kingdom by seeing what the data says about their infidelity. As it turns out, even in species where pair bonds are key to the social survival of the animals, reckless passion can play a big role in their breeding systems. Our host graciously brings us examples ranging from the expected (cuckoos, the species that gives us the word "cuckold") to the obscure (carrion beetles, whose relationship drama plays out in carcasses the world over).

Rachel's Sources:

•  Wysocki, D., et al (2023). Low level of extra-pair paternity in an urban population of blackbirds. The European Zoological Journal, 90(1), 307–312. https://doi.org/10.1080/24750263.2023.2193433

• Gao, L.-F., Zhang, H.-Y., Zhang, W., Sun, Y.-H., Liang, M.-J. and Du, B. (2020), Effects of extra-pair paternity and maternity on the provisioning strategies of the Azure-winged Magpie Cyanopica cyanus. Ibis, 162: 627-636. https://doi.org/10.1111/ibi.12800

• Li M-H, Välimäki K, Piha M, Pakkala T, Merilä J (2009) Extrapair Paternity and Maternity in the Three-Toed Woodpecker, Picoides tridactylus: Insights from Microsatellite-Based Parentage Analysis. PLoS ONE 4(11): e7895. https://doi.org/10.1371/journal.pone.0007895

• Niida, T., Yao, I., Nisimura, T. & Suzuki, S. (2024) Detection of extra-pair maternity in a carrion beetle under natural conditions. Ecological Entomology, 49(5), 734–738. Available from: https://doi.org/10.1111/een.13334

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Cancer is scary. A transmissible, STI-based cancer is even scarier. Canine Transmissible Venereal Tumor (CTVT) is the oldest, most prolific, cancer known in nature. And it's not alone. Nicole illustrates this bizarre disease which is expanding our understanding of cancer itself, and may have given one particular animal the key to immortality.

Nicole's Sources:

• Murchison, E., et al. 2014. Transmissible Dog Cancer Genome Reveals the Origin and History of an Ancient Cell Lineage. Science.
• Gori, K., et al. 2025. Horizontal transfer of nuclear DNA in transmissible cancer. PNAS.
• About Tasmanian devil facial tumor disease. Dept of Natural Resources and Environment Tasmania.
• Bruzos, A. 2022. Heterogeneity of cockle transmissible cancers. YouTube.
• Brain Bleach: Correia-Caeiro, C., Guo, K., Mills, D. 2020. Perception of dynamic facial expressions of emotion between dogs and humans. Animal Cognition.
• Hank Green. The Truth About the Single-Celled Dog. SciShow. YouTube.

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In honor of Pride Month, Rachel is taking us beneath the waves and beyond the binary into the fascinatingly queer world of fish! In this episode, she investigates stunningly fluid species that defy the concept of biological sex as an innate and immutable characteristic. SPOILER: Sex and gender in the animal kingdom is far from simple, guys. We should count ourselves lucky to live on such a beautifully un-boring planet. :)

Rachel's Sources:

1. Graves, J., & Todd, E. (2023, January 31). What we learn from fish that change sex. La Trobe University. https://www.latrobe.edu.au/news/articles/2020/opinion/what-we-learn-from-fish-that-change-sex
   1. Actual research: https://doi.org/10.1126/sciadv.aaw7006
2. R. Vega‐Frutis, R. Macías‐Ordóñez, R. Guevara, L. Fromhage, Sex change in plants and animals: a unified perspective, Journal of Evolutionary Biology, Volume 27, Issue 4, 1 April 2014, Pages 667–675, https://doi.org/10.1111/jeb.12333
3. Casas L, Saborido-Rey F. Environmental Cues and Mechanisms Underpinning Sex Change in Fish. Sex Dev. 2021;15(1-3):108-121. doi: 10.1159/000515274. Epub 2021 Jun 10. PMID: 34111868; PMCID: PMC8491468.
4. Munday PL, Buston PM, Warner RR. Diversity and flexibility of sex-change strategies in animals. Trends Ecol Evol. 2006 Feb;21(2):89-95. doi: 10.1016/j.tree.2005.10.020. Epub 2005 Nov 14. PMID: 16701480.

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Dancing, fighting, spreading sweet-smelling pheromones… all in the name of love. Lekking is a strange behavior that is a bit paradoxical in its hyper-competition but birds, frogs, bees, and even a few mammals all make it work. A male buffet where females have their pick of the best male, or perhaps a swanky second, and the males really don’t do much else but fight and dance.

Allan's Sources:

1. Kempenaers, Bart. (2022). Mating systems in birds. Current Biology. 32. R1115-R1121. 10.1016/j.cub.2022.06.066.
2. Kirkpatrick, M., Ryan, M. The evolution of mating preferences and the paradox of the lek. Nature 350, 33–38 (1991). https://doi.org/10.1038/350033a0
3. Rathore A, Isvaran K, Guttal V. 2023 Lekking as collective behaviour. Phil.Trans. R. Soc. B 378: 20220066. https://doi.org/10.1098/rstb.2022.0066

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What is catnip, what's its effect on cats, and is it really cats getting horny like so many think? Turns out these answers are a bit more complicated that we first thought.

Nicole's Sources:

1. Shi, X., et al.

Repellency of Novel Catnip Oils Against the Bed Bug (Hemiptera: Cimicidae) | Journal of Medical Entomology.

Oxford Academic.

1. Batume, C., et al. 2024.

Evaluating repellence properties of catnip essential oil against the mosquito species Aedes aegypti using a Y-tube olfactometer

. Scientific Reports.

1. Espín-Iturbe, L., et al. 2017.

Active and passive responses to catnip (Nepeta cataria) are affected by age, sex and early gonadectomy in male and female cats

. Behavioural Processes.

1. Johns Hopkins Medicine. 2019.

Deet Gives Humans an ‘Invisibilty Cloak’ to Fend Off Mosquito Bites

.

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(start the episode at 36:12 to avoid our discussion of all of the above, which are discussed in the context of "most dangerous courtship behaviors". we promise, it gets much sillier after that!)

Filthy Animals is back! We open Season 2 with some very important data-driven nonsense to settle some burning questions about the world of animal courtship. TO WIT: Which animals are mating in the most dangerous way possible, AND who is doing it the most obnoxiously? Danger and stupidity abound. Let the great debate begin!

Sources: Allan's Sources:

Ancel, A., Gilbert, C. & Beaulieu, M. The long engagement of the emperor penguin. Polar Biol 36, 573–577 (2013). https://doi.org/10.1007/s00300-013-1285-9

Biaggio MD, Sandomirsky I, Lubin Y, Harari AR, Andrade MC. Copulation with immature females increases male fitness in cannibalistic widow spiders. Biol Lett. 2016 Sep;12(9):20160516. doi: 10.1098/rsbl.2016.0516. PMID: 27651535; PMCID: PMC5046930.

Maydianne C. B. Andrade, Risky mate search and male self-sacrifice in redback spiders, Behavioral Ecology, Volume 14, Issue 4, July 2003, Pages 531–538, https://doi.org/10.1093/beheco/arg015

Rachel's Sources: Drop Dead! Female mate avoidance in an explosively breeding frog (2023) https://doi.org/10.1098/rsos.230742 

Breeding Mortality in the Wood Frog (2000) https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=1735&context=jaas

Mothers want brainy babies: https://news.cornell.edu/stories/2000/11/female-birds-choose-best-singers-have-smarter-offspring

Birds of the World - Golden-collared Manakin: https://birdsoftheworld.org/bow/species/gocman1/cur/introduction

Nicole's Sources:

Han, C., and Jablonski, P. 2010. Male water striders attract predators to intimidate females into copulation | Nature Communications.

CicadaMania.com 

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THIS IS OUR LAST EPISODE OF THE SEASON! We're taking a winter break, and we'll be back at the end of March with a new slate of episodes. Thanks for tagging along with us this year.

Wasp orgy videos [Source 3]: https://summit.sfu.ca/item/12712

Nicole's Sources:

1. Buchmann, S. 2023. What a Bee Knows: Exploring the Thoughts, Memories, and Personalities of Bees. Island Press.
2. Marshall, L., Alcock, J. 1981. The evolution of the mating system of the Carpenter bee Xylocopa varipuncta. Journal of Zoology.
3. Ablard, K. 2006. Local Mate Competition, and Mechanisms, Functions and Fitness Consequences of Courtship and Mating Behaviour in the Parasitoid Wasp Ooencyrtus kuvanae (Hymenoptera: Encyrtidae). Ph.D. Dissertation Simon Fraser University.

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In actuality, it's much more complicated, as pregnancy and childbirth in the wild leave mother and embryo alike vulnerable to environmental conditions, social constraints and hypercompetitive males. In this episode, Rachel tells us the many fascinating adaptations for reproductive control in mammals, showing the incredible capacity of animals to navigate the dangers of life before it even begins.

Content Warning: sexual content, abortion, pregnancy loss, infanticide (sensitive content begins at 31:28 of the episode)

Rachel's Sources:

1. Inzani, E., Marshall, H. H., Thompson, F. J., Kalema-Zikusoka, G., Cant, M. A., & Vitikainen, E. I. (2019). Spontaneous abortion as a response to reproductive conflict in the banded mongoose. Biology Letters, 15(12). https://doi.org/10.1098/rsbl.2019.0529
2. Feldhamer, G. A., Merritt, J. F., Krajewski, C., Rachlow, J. L., & Stewart, K. M. (2020). Mammalogy: Adaptation, diversity, ecology. Johns Hopkins University Press.
3. Bartoš, L., Dušek, A., Bartošová, J., Pluháček, J., & Putman, R. (2020). How to escape male infanticide: Mechanisms for avoiding or terminating pregnancy in mammals. Mammal Review, 51(1), 143–153. https://doi.org/10.1111/mam.12219
4. Heideman, P. D. (1989). Delayed development in Fischer’s pygmy fruit bat, Haplonycteris fischeri, in the Philippines. Reproduction, 85(2), 363–382. https://doi.org/10.1530/jrf.0.0850363

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Nicole's Sources:

1. Eleonora's Falcons imprison live birds for a later meal. 2015. MaghrebOrnitho. 
2. BirdLife Cyprus. 2022. Eleonora's Falcon - Life in the Balance. YouTube. 
3. Gayahan, G., Tschinkel, W. 2008. Fire Ants, Solenopsis invicta, Dry and Store Insect Pieces for Later Use. Journal of Insect Science. 
4. BBC Earth. David Attenborough Eats a Honeypot Ant. YouTube.

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Spending every moment of waking life trying to get laid has its downsides, and for some organisms, the business of reproduction is just too much of a hassle. So why bother with mating at all? If you want something done right, sometimes you just have to do it yourself. In this episode, Nicole runs down the fascinating asexual strategies of plants and animals, from self-printing bananas to all-female lizards to condor virgin birth.

Nicole's Sources:

1. Sexual Reproduction and the Evolution of Sex. Scitable.
2. Asexual Reproduction In Plants- Types and Methods. Byju’s.
3. Engelstädter J. 2008. Constraints on the evolution of asexual reproduction. Bioessays 30(11-12).
4. Osborne, M. 2022. Mice Birthed From Unfertilized Eggs for the First Time. Smithsonian Magazine.

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Koalas are well known for being disease ridden (at least in our circles) so lets talk about it. Chlamydia is highly contagious and deadly in koalas as well as birds, cows, and many other animals. This is a trip down sex education memory lane and details the horrible death that is untreated STIs.

Rachel's Primary Sources:

1. Wang, H., Jensen, J.-K., Olsson, A., Vorimore, F., Aaziz, R., Guy, L., Ellström, P., Laroucau, K., & Herrmann, B. (2020). Chlamydia psittaci in Fulmars on the Faroe Islands: A causative link to South American psittacines eight decades after a severe epidemic. Microbes and Infection, 22(8), 356–359.
2. Phillips, S., Quigley, B. L., Aziz, A., Bergen, W., Booth, R., Pyne, M., & Timms, P. (2019). Antibiotic treatment of chlamydia-induced cystitis in the koala is linked to expression of key inflammatory genes in reactive oxygen pathways. PLOS ONE, 14(8).
3. Van Wettere, A. J. (2020, February). Avian chlamydiosis - avian chlamydiosis. Merck Veterinary Manual.
4. Chen, C.-J., Casteriano, A., Green, A. C., & Govendir, M. (2023). A retrospective study on antibacterial treatments for koalas infected with chlamydia pecorum. Scientific Reports, 13(1).
5. Willson, G., & Cimon, K. Y. (2024, June 3). Bursa - cyst. National Institute of Environmental Health Sciences.

Secondary Sources:

1. Li, Z., Liu, P., Hou, J., Xu, G., Zhang, J., Lei, Y., Lou, Z., Liang, L., Wen, Y., & Zhou, J. (2020). Detection of Chlamydia psittaci and Chlamydia ibidis in the endangered crested ibis (nipponia nippon). Epidemiology and Infection, 148.
2. Marti, I., Pisano, S. R. R., & Wehrle, M. (2019). Severe conjunctivitis associated with chlamydia felis infection in a free-ranging Eurasian lynx (Lynx lynx). Journal of Wildlife Diseases, 55(2), 522.
3. Laroucau, K., Aaziz, R., Lécu, A., Laidebeure, S., et al. (2020). A cluster of Chlamydia Serpentis cases in captive snakes. Veterinary Microbiology, 240, 108499.
4. Laroucau, K., Ortega, N., Vorimore, F., et al. (2020). Detection of a novel chlamydia species in captive spur-thighed tortoises (Testudo Graeca) in southeastern Spain and proposal of Candidatus Chlamydia Testudinis. Systematic and Applied Microbiology, 43(2), 126071.
5. Laroucau, K., Vorimore, F., Aaziz, R., Solmonson, L., et al. (2019). Chlamydia buteonis, a new chlamydia species isolated from a red-shouldered hawk. Systematic and Applied Microbiology, 42(5), 125997.
6. Santoro M, Iaccarino D, Di Nocera F, Degli Uberti B et al. (2019). Molecular detection of Chlamydia abortus in a stranded Mediterranean striped dolphin Stenella coeruleoalba. Dis Aquat Org 132:203-208.

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Turns out lots of animals just wait around till maturity and then turn into horny little guys. The genus Antechinus is no exception as males will mate over and over until exhaustion.

Allan's Sources:

1. Book: “The Secret Lives of Carnivorous Marsupials” by Andrew Baker and Chris Dickman.
2. Kraaijeveld, K. et al. (2006) Does female mortality drive male semelparity in dasyurid marsupials? Proc Biol Sci. 2003 Nov 7; 270(Suppl 2): S251–S253.  doi: 10.1098/rsbl.2003.0082
3. Holleley CE et al. (2006). Size breeds success: multiple paternity, multivariate selection and male semelparity in a small marsupial, Antechinus stuartii. Mol Ecol. 2006 Oct;15(11):3439-48. doi: 10.1111/j.1365-294X.2006.03001.x. PMID: 16968281.
4. Brandies, P.A. et al. (2020). The first Antechinus reference genome provides a resource for pinvestigating the genetic basis of semelparity and age-related neuropathologies. GigaByte. 2020; 2020: gigabyte7. Published online 2020 Nov 5. doi: 10.46471/gigabyte.7
5. Zangrandi, P.L., Vieira, E.M. (2023). Semelparous Reproductive Strategy in New World Marsupials. In: Cáceres, N.C., Dickman, C.R. (eds) American and Australasian Marsupials. Springer, Cham. https://doi.org/10.1007/978-3-031-08419-5_19

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Nicole's Notable Sources:

1. Heiduk, A., Brake, I., Tolasch, T., Frank, J., Jurgens, A., Meve, U., Dotterl, S. 2010. Scent chemistry and pollinator attraction in the deceptive trap flowers of Ceropegia dolichophylla. South African Journal of Botany.
2. Greenhood orchid. YouTube. Shows trap mechanism.

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Rachel's Sources:

1. Arikawa, K. 2001. Hindsight of Butterflies: The Papilio butterfly has light sensitivity in the genitalia, which appears to be crucial for reproductive behavior. BioScience.
2. Arikawa, K. 2009. Genital Photoreceptors Have Crucial Role in Oviposition in Japanese Yellow Swallowtail Butterfly, Papilio xuthus. Zoological Science.

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Allan's Sources:

1. De Waal, Franz. Bonobos: The Forgotten Ape. 1st ed., published 1997.
2. De Waal, Franz. “Bonobo Sex and Society”, Scientific American. June 1, 2006.
3. https://www.scientificamerican.com/article/bonobo-sex-and-society-2006-06/
4. Annicchiarico, G., Bertini, M., Cordoni, G., & Palagi, E. (2020). Look at me while having sex! Eye-to-eye contact affects homosexual behaviour in bonobo females. Behaviour, 157(10-11), 949-970. https://doi.org/10.1163/1568539X-bja10034
5. Gruber T, Clay Z. A Comparison Between Bonobos and Chimpanzees: A Review and Update. Evol Anthropol. 2016 Sep;25(5):239-252. doi: 10.1002/evan.21501. PMID: 27753219.

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Science educators will talk about the unusual adult activities of the natural world that we believe you need to know about. Every month, we’ll expose you to the latest research on all the filthy topics your high school science teacher was too embarrassed to talk about.

This podcast is produced by Grassland Groupies, and the music for this trailer is from Haydn London Trios, Hob. IV:1-3, accessed through MusOpen.

See you on April 25!