The sex life of the Monarch butterfly is positively wild

Wendy Williams is an enthusiast, and enthusiasm is infectious. Lepidoptery is for her a new fascination, and it shows. On the plus side, her excitement shimmers as freshly as a newly-hatched Adonis Blue. She marvels, and makes us marvel, at the miracles she discovers.

She wonders at the strangeness of a butterfly’s proboscis, which is not, as it appears, a drinking straw (even butterflies cannot suck through a straw longer than their own bodies), but works by capillary action, blotting up fluids and sending saliva down to dissolve sticky or solid secretions. Moths show more variety in their diet, as adults as well as caterpillars — but then there are more than 160,000 known species of moth, and fewer than 20,000 butterflies: there are vampire ones in Siberia and a moth in Madagascar which uses its barbed proboscis to harpoon the eyelids of sleeping birds and drink their tears.

Williams concentrates on butterflies, and chiefly on one species, the Monarch. This is famous for its autumnal mass migrations, flying from as far north as Canada to Florida or California, or down the eastern side of the continent to Mexico. Over-wintering, tens of thousands cluster for warmth on a single conifer and their weight can break branches. In the spring, they become reproductive again, and new butterflies will work their way back up north in successive generations within a single season. Only a specially long-lived ‘super-generation’ will travel up to 3,000 miles south again in the autumn.

That, as Williams would say, is ‘wild’ or ‘cool’. Following the Monarchs, she is amazed by how tough and intelligent they are; how mysterious their navigational skills; how strange their opalescent colours, some created not by pigments but by the reflecting and refracting structures of the scales on their wings; and how alien their compound eyes (they have many more eye-cones than we do and see colours beyond our range. A Cabbage White would be a Cabbage Ultra-violet to another of the species). En route, she gleans fascinating material from the fellow enthusiasts she meets.

Sometimes, however, there are lacunae in her acquired knowledge. She writes about Vladimir Nabokov, who acquired fame as a lepidopterist as well as an author, discovering the Karner Blue; but she is oddly vague about his pioneering work, which involved

“carefully dissecting specimens so as to study their genitalia. (This wasn’t necessarily salacious: lepidopterists commonly study genitalia in order to determine, among other things, the sex of butterflies.)

I like that ‘necessarily’, as if the author of Lolita could source a prurient thrill within the tiniest cranny.

But sexing moths is not the main point of studying their genitalia — ‘a most rewarding past-time’, according to my not overtly pornographic Field Guide to the Micro Moths of Great Britain and Ireland. Moths and butterflies have intricate genital structures, unique to each species, which act as a miniature lock-and-key mechanism for mating. Species groups which are difficult to separate by wing-pattern alone are relatively easy to identify individually by their genitalia; and families and groups within families possess similar structures.

In the days before DNA, these were an invaluable tool not only for species identification but also for working out evolutionary taxonomy. This is what the moth-fiddling Nabokov was doing in 1945 when he posited the evolutionary pathway (via the Bering Straits) from Old World to New World Poly-ommatus Blues. It took until 2011 for DNA testing to prove him right. He also, incidentally, spotted the ‘barbaric pact’ between Large Blues and ants: ‘It was as if cows gave us Chartreuse and we gave them our infants to eat.’

Actually, Williams is also missing some ‘wild’ facts about the sex life of Monarch butterflies. (Warning: when I wrote Nature Notes for our parish magazine, I received complaints that there was ‘too much sex’ in them, after some pretty hot stuff about slugs. I hope Spectator readers are more robust.) ‘The Monarch butterfly could well be designated nature’s prime example of the male chauvinistic pig,’ Miriam Rothschild wrote in 1978, describing how males knock down females to take them by force. But recent research shows that exercising this droit du seigneur comes at a cost. Monarchs produce ejaculate in huge, impenetrably wrapped packages called ‘spermatophores’. Each can be up to 10 per cent of the body weight of the male — the equivalent for a human of a couple of gallons — which must take it out of a guy.

Indeed, the package contains not just sperm but also proteins, as a bonus for the mother of his children; and these proteins cannot be replenished from the nectar supped as an adult. They deplete his stock of ‘precious bodily fluids’ laid up from his eating days as a very hungry caterpillar, severely limiting the number of times each male can have sex.

The tough packaging of a spermatophore is designed to delay the female from mating with a rival. No natural chemicals can dissolve it (in the laboratory, scientists use boiling concentrated sulphuric acid); but it is deposited in the bursa copulatrix of the female, which has ‘a row of large chitinous teeth on either side of the organ’. In other words, the female possesses that Freudian nightmare, the vagina dentata, and chomps her way through the indigestible wrapping…

Even without this lurid top-spin, Williams’s account is fascinating. Some will find her American style either winning, as I did, or irritating. To English ears it can sound odd. ‘Cantankerous lupines’ are not grumpy wolves — but how can plants be cantankerous? And Victorian British picnickers lie ‘lollygagging on the grass’ (Dot Wordsworth would observe that in 1868 this word had improper connotations.) But I do recommend this book. Readers will find themselves repeatedly passing on snippets. Did you know that butterfly scales are helping bio-designers to create devices to help asthma sufferers?