Entomology, chemical ecology, evidence-based environmentalism and science in general. I like big bugs and I cannot lie.

Saturday 24 January 2015

Small lives of the turning year

I've recently been lucky enough to make a friend who feels as passionately about reptiles as I do about insects, who understands the urge to complain about Tumblr photoshops and sympathizes with my complaint that they used THE WRONG TYPE OF MAGGOT in the peach in the film Labyrinth instead of edging slowly away and suddenly becoming very very busy whenever I contact her. We were discussing our favorite creatures and I realised that while there are plenty of insects and other invertebrates whose biology I find fascinating, my personal favourites amongst the ones I encounter in my own garden and landscape are the ones that I strongly associate with a particular time of year.

Male maybug, Melolontha melolontha, image from Wikipedia
Undoubtedly my favorite insect is the Maybug, Melolontha melolontha. Although it's not technically a bug, and technically it's a pest because the larvae eat crop roots (less of an issue now as it was almost wiped out last century) I absolutely adore these big bumbling beetles. They fly about in the afternoon and at dusk, buzzing like little bomber planes, and crash most unaerobatically into anything in their path with a loud thump. The males also have amazing little feathery antennae, the fronds of which increase their surface area to pick up the females' scent, allowing them to locate a mate.

I think my love for them may have developed as a child - there are very few insects in Britain large and docile enough to be picked up and petted, and they'll happily explore your hand on tiny pinscratch claws. (Sadly they were apparently also a favourite with children in less enlightened times, who apparently came up with all sorts of horrible things to do to them.) And last but by no means least, their common name, cockchafer, sounds rather rude!

As their name suggests, maybugs usually start to fly in May. As well as being fascinating in their own right, to me they've always held associations with the beginning of summer, with the arrival of hot lazy days and long golden evenings. I rarely see them now living in London - in my eight years here I've found a single one - and I miss these holiday heralds in the city.

Winged black ants, image by Rebecca Nesbit
For most of the year the Common Black Ant Lasius niger seems fairly unremarkable, but a closer look reveals it to be anything but. For a start they farm aphids, protecting them from predators in order to "milk" them for the honeydew they produce. As every gardener knows, aphids can be pests of plants, sucking the sap and introducing disease. Plant sap is very rich in sugar but has a comparatively low concentration of amino acids, the building blocks of protein, so to get all the protein they need aphids have to take in far more sugar than they could possibly use. They get rid of the excess by excreting a concentrated sugary solution known as honeydew, which to an ant serves as a very convenient sweet energy drink. 

Interestingly, this process is thought to be the reason plants evolved sweet nectar to attract pollinators - having ants guarding their tiny herds benefited the plants too, as ants will eat herbivorous insects as happily as they'll eat aphid predators. Obviously though having their sap sucked by the aphids was a bit of a downside to the arrangement, so plants evolved ways of producing their own sugary secretions, mimicking the aphids to attract the ants. Over time the additional benefit of using highly mobile insects to transport their pollen between plants producing these sugary secretions emerged.

Incidentally this entire system of interactions is utterly fascinating and deserves far more than two paragraph's worth of explanation, but I haven't managed to find a single layperson's introduction to link to so I may have to write my own.

What makes common black ants such a dramatic seasonal indicator though is their mating flights; every year between June and September vast swarms of winged males and immature Queens emerge from their nests to mate and establish new colonies. Although a survey carried out by the Society of Biology revealed that ants did not all mate on a single day across the country as had commonly been supposed, mating flights are coordinated in local areas to produce localised "flying ant days".

When I was a child my family and another used to go on holiday together to the Isle of Wight every summer, driving down with a gaggle of children crammed into the footwells of the car in a way that would be illegal now and probably was then to be honest. We always seemed to manage to arrive in time for the flying ants and while everyone else was picking them out of sandwiches or scraping them off sunscreened limbs, a firm association somehow became cemented in my brain between flying ants and all the good things in life.

Female common green grasshopper, Omocestus viridulus,
image from Wikipedia
I know I'm cheating a little here by not picking a single species, but others insect I associate very strongly with high summer are the crickets and grasshoppers (there's a good explanation of the difference here. Grasshoppers are active during the day, unlike crickets which tend to be active at dusk, and they are most active in warm weather. As warm weather is also when I'm most likely to be found sprawling on the grass, in summer when the sun has baked the grass roots almost to straw is the time when we're most likely to bump into each other and nothing says "camping holiday" quite like having a grasshopper suddenly materialise on the page of the book you're reading only to spring away again at the slightest shifting of your fingers. And there can be few people for whom their trilling song doesn't evoke lazy summer days.

Female Araneus diadematus. Image from Wikipedia.

As summer comes to an end and the autumn evenings draw in, misty and mysterious, Britain's spiders really come into their own, festooning the garden with their silken webs. The most skilful weaver is the garden spider, Araneus diadematus.

The spiders themselves are as beautiful as their webs, with a wide variety of colours from restrained neutral tones of taupe and dove grey to rich deep chocolate and mahogany or sunny gold, and when the females are gravid their abdomens are large enough to notice the cross-shaped markings and really appreciate the intricate stippled patterns. There are some gorgeous pictures showing various different colourations here, or I would really recommend doing a Google image search for all the beautiful pictures I can't share because they're not public domain.

Special mention too should be given to the various species of house spiders which wander indoors in autumn in search of a mate and instead tend to meet a swift and crunchy end at the paws of the cat, who unfortunately views most invertebrates as entertaining snacks. The Natural History Museum produces a handy guide to the most common species likely to be found indoors which is available here (pdf).

Compost, image from Wikipedia. Okay I'm cheating a bit with this one but I defy anyone to find an artistic, Creative Commons licensed image of a worm.
Invertebrate life is less apparent in winter, when most cold-blooded creatures burrow down into the ground or huddle in cracks and crevices to wait for the return of the warm days. One species I still encounter on a weekly basis though is the horde of composting worms (Eisenia spp) that live in my garden wormery (pdf), eating through our kitchen waste and producing compost. Although they slow down in winter the wormery is insulated and the decay of compost making generates its own heat so they keep working all year round. 

Worms may not be the most charismatic creatures in the garden it's true, but I find it amazing that something that is essentially a stripy tube can bring about such a miraculous transmutation, turning mouldering kitchen leftovers into dark, crumbly compost that you'll want to sniff deeply at and run through your fingers when it's warmed by the springtime sun. Their distant cousins the earthworms do this vital recycling job on a much larger scale in the garden soil, keeping nutrients flowing ceaselessly through the ecosystem. I find the whole concept of nutrient cycles deeply comforting on an almost spiritual level as a reminder that we're all connected, humans and soil and microorganisms and vegetables, we're all made of the same things on a fundamental level, and we have worms to thank for the fact that these fundamental building blocks are constantly in motion, in flux through a greater whole.

Buff-tailed bumblebee,  Bombus terrestris, image from Wikimedia Commons
Some of the first insects to reappear in spring  are the bumblebees. There are numerous common species in Britain, which can be distinguished by their markings.  Unlike honeybees, only the queens of these fuzzy, large-bodied bee species survive the winter, by hibernating underground. In spring she must first build her own nest and forage for nectar and pollen herself before she can start creating her brood of minions.

All cold-blooded creatures are sluggish on chilly early spring mornings and struggle to get moving (I can sympathise) but bumblebees are able to decouple their flight muscles from their wings and use them to generate body heat which allows them to fly earlier in the year than most other insects, as this thermal video shows.

Large bee-fly Bombylius major, image from Wikimedia Commons.
Another spring arrival often confused with bumblebees are the various species of bee-flies. In spite of their appearance these are actually diptera not bees, true two-winged flies like houseflies or greenbottles. Their appearance mimics that of bees to deter predators, and like bees the adults feed on nectar using their long proboscis to visit early spring flowers like primroses and violets. A lot of people who've contacted me to identify them find this proboscis quite alarming, but it's for flowers only and they don't harm humans.  Bees themselves are a different matter though - bee-flies are parasites of solitary bees, shooting their eggs into bees' tunnels where the vampire-like larve parasities the young bees. Which just goes to show you can't trust anything cute and fluffy.

The large bee-fly incidentally has the glorious binomial name of Bombylius major, which always makes me think of a rather pompous and portly retired military gentleman.

13th century depiction of the turning of the seasons from
Liber Divinorum Operum by Hildegard von Bingen
I have been through some difficult times in the past, and through them I took great comfort from the changing of the seasons, from the knowledge that nothing was permanent and that winter would inevitably be followed by spring. It was reassuring to know that whatever happened to me, whatever struggles I may have had or mistakes I made in my personal life, the Earth would continue on its path around the sun. The days would lengthen and shorten in their predictable cycles, sap would rise and fall, living things would wake and rise and feed and breed and sleep just as they had always done and would always do.  The constant novelty of the turning year gave me reasons to hope too, the knowledge that if I just held on a little longer I would see snowdrops and daffodils and hawthorn blossom, I would taste strawberries warm from the sun and English apples and little oranges smelling of warmth and spice and Christmas, I would see bees on lavender and peacock butterflies and cobwebs like jeweled lace.

The tiny invertebrate lives beneath our feet are so often overlooked in the when we appreciate the endless variety of the circling year. I hope this post will encourage some people to look for them, and note them, and smile.

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