Monarch Butterfly from https://animalia.bio/monarch-butterfly
Dear Readers, after the rather sad poem that I featured on Thursday, I was fascinated to read in New Scientist that there is evidence that Monarch Butterflies, and some other species, ‘self-medicate’. Lots of animals have been found to seek out things that they seem to know will help them get better when they’re sick – think of all the animals that seek out mineral licks, for example, or the way that cats and dogs sometimes eat grass. But to my knowledge, no one has previously found this behaviour in invertebrates.
Jaap de Roode has a new book ‘Doctors by Nature: How Ants, Apes and Other Animals Heal Themselves‘, and very fascinating it is too. First up, those Monarch Butterflies. They are prone to being infected by a parasite (Ophrycystis elektroscirrha), a protozoan that infects female Monarchs and then passes on to their caterpillars when they eat their egg shells. It’s been found that when the females are infected, they preferentially feed on milkweeds which are high in chemicals called cardenolides, which are toxic to the parasite. The species of milkweed which is most poisonous, Tropical Milkweed (Asclepias curassavica) is now widely planted across the Monarch’s range. This is a controversial plant in other ways because its flowering period can disrupt the Monarch’s migration |(keeping it in the north when it should be heading south) but nonetheless this is a very interesting observation.
Garden Tiger caterpillar (Arctica caja) Photo by Gail Hampshire at https://www.flickr.com/photos/gails_pictures/52962034953
Next, my beloved ‘woolly bear’ caterpillars (the larvae of any species of Tiger Moth) increase their consumption of plants containing alkaloids when they are parasitized by flies. How does that work? De Roode points out that the researchers in the woolly bear study have really looked into the detail. Caterpillars have four different taste receptors (not so different from us actually) and one of those receptors recognises the taste of the alkaloid. When the caterpillars are infected, that particular taste receptor starts to fire more frequently, so the nerve impulses to the brain encourage the caterpillar to seek out that particular taste.
De Roode thinks that self-medication in the animal kingdom is much more widespread than we usually think, and in many areas of the world, native peoples have observed what plants the animals use, and have then experimented with it themselves, discovering new treatments along the way. We are discovering so much about invertebrates, and de Roode is undoubtedly right when he wonders what other animals use to self-medicate, What does an octopus take if it has a headache, I wonder?
And finally, here’s an interesting (and commoner) take on one particular self-medication behaviour, anointing. This is what a cat does when it rolls around on a patch of catmint, or plays with a catnip toy. Clearly, the animal is having a great time, but what’s going on? Interestingly, scientists in Japan have discovered that when catmint is crushed, it releases a chemical that repels mosquitoes. A cat doesn’t need to know that’s what’s happening, but cats who have this behaviour may have had a better survival rate in the Middle East, which is thought to be the origin point for domestic cats. Nowadays most UK cats don’t need to worry about mosquitoes (yet, but I suspect climate change is saying ‘hold my beer’), but many still behave like twits when they smell catmint.
Frankie the Cat on Catnip – Photo by Marcy Leigh at https://www.flickr.com/photos/marcyleigh/18375701278